
Characterization of topological phases of dimerized Kitaev chain via edge correlation functions Phys. Rev. B (IF 3.836) Pub Date : 20171120
Yucheng Wang, JianJian Miao, HuiKe Jin, and Shu ChenWe study analytically topological properties of a noninteracting modified dimerized Kitaev chain and an exactly solvable interacting dimerized Kitaev chain under open boundary conditions by analyzing two introduced edge correlation functions. The interacting dimerized Kitaev chain at the symmetry point Δ = t and the chemical potential μ = 0 can be exactly solved by applying two JordanWigner transformations and a spin rotation, which permits us to calculate the edge correlation functions analytically. We demonstrate that the two edge correlation functions can be used to characterize the trivial, SuSchriefferHeegerlike topological and topological superconductor phases of both the noninteracting and interacting systems and give their phase diagrams.

Single layers and multilayers of GaN and AlN in squareoctagon structure: Stability, electronic properties, and functionalization Phys. Rev. B (IF 3.836) Pub Date : 20171120
E. Gürbüz, S. Cahangirov, E. Durgun, and S. CiraciFurther to planar singlelayer hexagonal structures, GaN and AlN can also form freestanding, singlelayer structures constructed from squares and octagons. We performed an extensive analysis of dynamical and thermal stability of these structures in terms of ab initio finitetemperature molecular dynamics and phonon calculations together with the analysis of Raman and infrared active modes. These singlelayer squareoctagon structures of GaN and AlN display directional mechanical properties and have wide, indirect fundamental band gaps, which are smaller than their hexagonal counterparts. These density functional theory band gaps, however, increase and become wider upon correction. Under uniaxial and biaxial tensile strain, the fundamental band gaps decrease and can be closed. The electronic and magnetic properties of these singlelayer structures can be modified by adsorption of various adatoms, or by creating neutral cationanion vacancies. The singlelayer structures attain magnetic moment by selected adatoms and neutral vacancies. In particular, localized gap states are strongly dependent on the type of vacancy. The energetics, binding, and resulting electronic structure of bilayer, trilayer, and threedimensional (3D) layered structures constructed by stacking the single layers are affected by vertical chemical bonds between adjacent layers. In addition to van der Waals interaction, these weak vertical bonds induce buckling in planar geometry and enhance their binding, leading to the formation of stable 3D layered structures. In this respect, these multilayers are intermediate between van der Waals solids and wurtzite crystals, offering a wide range of tunability.

Openboundary reflection of quantum well states at Pb(111) Phys. Rev. B (IF 3.836) Pub Date : 20171120
M. Müller, N. Néel, S. Crampin, and J. KrögerUsing a scanning tunneling microscope, confined electron states are studied that exist above subsurface nanometersized voids at Pb(111), where potential barriers at the parallel vacuumPb(111) and Pb(111)void interfaces establish a principal series of quantum well states that are further confined laterally by strong reflection at the open boundaries at the edges of the void. The influence of the size, depth, and shape of the voids on the effectiveness of the lateral confinement is discussed. Standing wave patterns observed in differential conductance maps unravel the dispersion of the relevant underlying Pb electron states.

Spincharge conversion in disordered twodimensional electron gases lacking inversion symmetry Phys. Rev. B (IF 3.836) Pub Date : 20171120
Chunli Huang, Mirco Milletarì, and Miguel A. CazalillaWe study the spincharge conversion mechanisms in a twodimensional gas of electrons moving in a smooth disorder potential by accounting for both Rashbatype and Mott's skew scattering contributions. We find that the quantum interference effects between spinflip and skew scattering give rise to anisotropic spin precession scattering (ASP), a direct spincharge conversion mechanism that was discovered in an earlier study of graphene decorated with adatoms [Huang et al., Phys. Rev. B 94, 085414 (2016)]. Our findings suggest that, together with other spincharge conversion mechanisms such as the inverse galvanic effect, ASP is a fairly universal phenomenon that should be present in disordered twodimensional systems lacking inversion symmetry.

Spinpolarized ballistic conduction through correlated AuNiMnSbAu heterostructures Phys. Rev. B (IF 3.836) Pub Date : 20171120
C. Morari, W. H. Appelt, A. Östlin, A. PrinzZwick, U. Schwingenschlögl, U. Eckern, and L. ChioncelWe examine the ballistic conduction through AuNiMnSbAu heterostructures consisting of up to four units of the halfmetallic NiMnSb in the scattering region, using density functional theory (DFT) methods. For a single NiMnSb unit the transmission function displays a spin polarization of around 50 % in a window of 1 eV centered around the Fermi level. By increasing the number of layers, an almost complete spin polarization of the transmission is obtained in this energy range. Supplementing the DFT calculations with local electronic interactions, of Hubbardtype on the Mn sites, leads to a hybridization between the interface and manybody states. The significant reduction of the spin polarization seen in the density of states is not apparent in the spin polarization of the conduction electron transmission, which suggests that the hybridized interface and manybody induced states are localized.

Optical conductivity of a twodimensional metal near a quantum critical point: The status of the extended Drude formula Phys. Rev. B (IF 3.836) Pub Date : 20171120
Andrey V. Chubukov and Dmitrii L. Maslov 
Spinorbit coupling, optical transitions, and spin pumping in monolayer and fewlayer InSe Phys. Rev. B (IF 3.836) Pub Date : 20171120
S. J. Magorrian, V. Zólyomi, and V. I. Fal'koWe show that spinorbit coupling (SOC) in InSe enables the optical transition across the principal band gap to couple with inplane polarized light. This transition, enabled by p x , y ↔ p z hybridization due to intraatomic SOC in both In and Se, can be viewed as a transition between two dominantly s  and p z orbital based bands, accompanied by an electron spinflip. Having parametrized k · p theory using firstprinciples density functional theory we estimate the absorption for σ ± circularly polarized photons in the monolayer as ∼ 1.5 %, which saturates to ∼ 0.3 % in thicker films (3–5 layers). Circularly polarized light can be used to selectively excite electrons into spinpolarized states in the conduction band, which permits optical pumping of the spin polarization of In nuclei through the hyperfine interaction.

Chemically exfoliatedMoS2layers: Spectroscopic evidence for the semiconducting nature of the dominant trigonal metastable phase Phys. Rev. B (IF 3.836) Pub Date : 20171120
Banabir Pal, Anjali Singh, Sharada G., Pratibha Mahale, Abhinav Kumar, S. Thirupathaiah, H. Sezen, M. Amati, Luca Gregoratti, Umesh V. Waghmare, and D. D. SarmaA metastable trigonal phase, existing only as small patches on a chemically exfoliated fewlayered, thermodynamically stable 1 H phase of Mo S 2 , is believed to critically influence the properties of Mo S 2 based devices. The electronic structure of this metastable phase is little understood in the absence of a direct experimental investigation of its electronic properties, complicated further by conflicting claims from theoretical investigations. We address this issue by investigating the electronic structure of this minority phase in chemically exfoliated Mo S 2 fewlayered systems by enhancing its contributions with the use of highly spatially resolved ( ≤ 120 nm resolution) photoemission spectroscopy and Raman spectroscopy in conjunction with stateoftheart electronic structure calculations. Based on these results, we establish that the ground state of this phase, arrived at by the chemical exfoliation of Mo S 2 using the usual Li intercalation technique, is a small gap ( ∼ 90 ± 40 meV ) semiconductor in contrast to most claims in the literature; we also identify the specific trigonal structure it has among many suggested ones.

Anisotropic pseudopotential characterization of quantum Hall systems under a tilted magnetic field Phys. Rev. B (IF 3.836) Pub Date : 20171120
Bo Yang, Ching Hua Lee, Chi Zhang, and ZiXiang HuWe analytically derived the effective twobody interaction for a finite thickness quantum Hall system with a harmonic perpendicular confinement and an inplane magnetic field. The anisotropic effective interaction in the lowest Landau level (LLL) and first Landau level (1LL) are expanded in the basis of the generalized pseudopotentials (PPs), and we analyze how the coefficients of some prominent isotropic and anisotropic PPs depend on the thickness of the sample and the strength of the inplane magnetic field. We also investigate the stability of the topological quantum Hall states, especially the Laughlin state and its emergent guiding center metric, which we can now compute analytically. An interesting reorientation of the anisotropy direction of the Laughlin state in the 1LL is revealed, and we also discuss various possible experimental ramifications for this quantum Hall system with broken rotational symmetry.

Quantum field theory of Xcube fracton topological order and robust degeneracy from geometry Phys. Rev. B (IF 3.836) Pub Date : 20171120
Kevin Slagle and Yong Baek KimWe propose a quantum field theory description of the Xcube model of fracton topological order. The field theory is not (and cannot be) a topological quantum field theory (TQFT) since, unlike the Xcube model, TQFTs are invariant (i.e., symmetric) under continuous spacetime transformations. However, the theory is instead invariant under a certain subgroup of the conformal group. We describe how braiding statistics and groundstate degeneracy are reproduced by the field theory, and how the the Xcube Hamiltonian and field theory can be minimally coupled to matter fields. We also show that even on a manifold with trivial topology, spatial curvature can induce a groundstate degeneracy that is stable to arbitrary local perturbations! Our formalism may allow for the description of other fracton field theories, where the only necessary input is an equation of motion for a charge density.

Principal component analysis for fermionic critical points Phys. Rev. B (IF 3.836) Pub Date : 20171120
Natanael C. Costa, Wenjian Hu, Z. J. Bai, Richard T. Scalettar, and Rajiv R. P. SinghWe use determinant quantum Monte Carlo (DQMC), in combination with the principal component analysis (PCA) approach to unsupervised learning, to extract information about phase transitions in several of the most fundamental Hamiltonians describing strongly correlated materials. We first explore the zerotemperature antiferromagnet to singlet transition in the periodic Anderson model, the Mott insulating transition in the Hubbard model on a honeycomb lattice, and the magnetic transition in the 1/6filled Lieb lattice. We then discuss the prospects for learning finite temperature superconducting transitions in the attractive Hubbard model, for which there is no sign problem. Finally, we investigate finite temperature charge density wave (CDW) transitions in the Holstein model, where the electrons are coupled to phonon degrees of freedom, and carry out a finite size scaling analysis to determine T c . We examine the different behaviors associated with HubbardStratonovich auxiliary field configurations on both the entire spacetime lattice and on a single imaginary time slice, or other quantities, such as equaltime Green's and pairpair correlation functions.

Highpressure versus isoelectronic doping effect on the honeycomb iridateNa2IrO3 Phys. Rev. B (IF 3.836) Pub Date : 20171120
V. Hermann, J. EbadAllah, F. Freund, I. M. Pietsch, A. Jesche, A. A. Tsirlin, J. Deisenhofer, M. Hanfland, P. Gegenwart, and C. A. KuntscherWe study the effect of isoelectronic doping and external pressure in tuning the ground state of the honeycomb iridate Na 2 IrO 3 by combining optical spectroscopy with synchrotron xray diffraction measurements on single crystals. The obtained optical conductivity of Na 2 IrO 3 is discussed in terms of a Mottinsulating picture versus the formation of quasimolecular orbitals and in terms of Kitaev interactions. With increasing Li content x , ( Na 1 − x Li x ) 2 IrO 3 moves deeper into the Mottinsulating regime, and there are indications that up to a doping level of 24% the compound comes closer to the Kitaev limit. The optical conductivity spectrum of singlecrystalline α − Li 2 IrO 3 does not follow the trends observed for the series up to x = 0.24 . There are strong indications that α − Li 2 IrO 3 is not as close to the Kitaev limit as Na 2 IrO 3 and lies closer to the quasimolecular orbital picture instead. Except for the pressureinduced hardening of the phonon modes, the optical properties of Na 2 IrO 3 seem to be robust against external pressure. Possible explanations of the unexpected evolution of the optical conductivity with isolectronic doping and the drastic change between x = 0.24 and x = 1 are given by comparing the pressureinduced changes of lattice parameters and the optical conductivity with the corresponding changes induced by doping.

Entanglement spectroscopy on a quantum computer Phys. Rev. B (IF 3.836) Pub Date : 20171120
Sonika Johri, Damian S. Steiger, and Matthias Troyer 
Amplitude mode oscillations in pumpprobe photoemission spectra from adwave superconductor Phys. Rev. B (IF 3.836) Pub Date : 20171120
B. Nosarzewski, B. Moritz, J. K. Freericks, A. F. Kemper, and T. P. DevereauxRecent developments in the techniques of ultrafast pumpprobe photoemission have made possible the search for collective modes in strongly correlated systems out of equilibrium. Including inelastic scattering processes and a retarded interaction, we simulate time and angleresolved photoemission spectroscopy (trARPES) to study the amplitude mode of a d wave superconductor, a collective mode excited through the nonlinear lightmatter coupling to the pump pulse. We find that the amplitude mode oscillations of the d wave order parameter occur in phase at a single frequency that is twice the quasisteadystate maximum gap size after pumping. We comment on the necessary conditions for detecting the amplitude mode in trARPES experiments.

Magnetic solitons and magnetic phase diagram of the hexagonal chiral crystalCrNb3S6in oblique magnetic fields Phys. Rev. B (IF 3.836) Pub Date : 20171120
Junichiro Yonemura, Yusuke Shimamoto, Takanori Kida, Daichi Yoshizawa, Yusuke Kousaka, Sadafumi Nishihara, Francisco Jose Trindade Goncalves, Jun Akimitsu, Katsuya Inoue, Masayuki Hagiwara, and Yoshihiko TogawaWe investigate the magnetic torque and magnetoresistance (MR) responses in oblique magnetic fields in micrometersized specimens of the hexagonal chiral magnetic crystal CrNb 3 S 6 . The results exhibit hysteresis over a wide range of applied field angles, while reversible behavior appears only when the magnetic field is closely aligned to the helical axis of the crystal. Stepwise changes of the magnetic torque and MR detected in the hysteresis region indicate the existence of chiral solitons in the oblique magnetic fields. A magnetic phase diagram is derived from the experimental results, and the stability of the chiral magnetic phases, such as the chiral soliton lattice and chiral conical phase, and the nature of the phase transition between them are discussed.

Magneticfieldinduced decrease of the spin Peltier effect inPt/Y3Fe5O12system at room temperature Phys. Rev. B (IF 3.836) Pub Date : 20171120
Ryuichi Itoh, Ryo Iguchi, Shunsuke Daimon, Koichi Oyanagi, Kenichi Uchida, and Eiji SaitohWe report the observation of magneticfieldinduced decrease of the spin Peltier effect (SPE) in a junction of a paramagnetic metal Pt and a ferrimagnetic insulator Y 3 Fe 5 O 12 (YIG) at room temperature. For driving the SPE, spin currents are generated via the spin Hall effect from applied charge currents in the Pt layer, and injected into the adjacent thick YIG film. The resultant temperature modulation is detected by a commonly used thermocouple attached to the Pt/YIG junction. The output of the thermocouple shows sign reversal when the magnetization is reversed and linearly increases with the applied current, demonstrating the detection of the SPE signal. We found that the SPE signal decreases with the magnetic field. The observed decreasing rate was found to be comparable to that of the spin Seebeck effect (SSE), suggesting the dominant and similar contribution of the lowenergy magnons in the SPE as in the SSE.

Coupling of structure to magnetic and superconducting orders in quasionedimensionalK2Cr3As3 Phys. Rev. B (IF 3.836) Pub Date : 20171120
K. M. Taddei, Q. Zheng, A. S. Sefat, and C. de la CruzQuasionedimensional A 2 Cr 3 As 3 (with A = K , Cs, Rb) is an intriguing new family of superconductors which exhibit many similar features to the cuprate and ironbased unconventional superconductor families. Yet, in contrast to these systems, no charge or magnetic ordering has been observed which could provide the electronic correlations presumed necessary for an unconventional superconducting pairing mechanism—an absence which defies predictions of firstprinciples models. We report the results of neutron scattering experiments on polycrystalline K 2 Cr 3 As 3 ( T c ∼ 7 K ) which probed the lowtemperature dynamics near T c . Neutron diffraction data evidence a subtle response of the nuclear lattice to the onset of superconductivity while inelastic scattering reveals a highly dispersive column of intensity at the commensurate wave vector q = 00 1 2 which loses intensity beneath T c —indicative of shortrange magnetic fluctuations. Using linear spinwave theory, we model the observed scattering and suggest a possible structure to the shortrange magnetic order. These observations suggest that K 2 Cr 3 As 3 is in close proximity to a magnetic instability and that the incipient magnetic order both couples strongly to the lattice and competes with superconductivity, in direct analogy with the ironbased superconductors.

Dopinginduced quantum crossover inEr2Ti2−xSnxO7 Phys. Rev. B (IF 3.836) Pub Date : 20171120
M. Shirai, R. S. Freitas, J. Lago, S. T. Bramwell, C. Ritter, and I. ŽivkovićWe present the results of the investigation of magnetic properties of the Er 2 Ti 2 − x Sn x O 7 series. For small doping values, the ordering temperature decreases linearly with x , while the moment configuration remains the same as in the x = 0 parent compound. Around x = 1.7 doping level, we observe a change in the behavior, where the ordering temperature starts to increase and new magnetic Bragg peaks appear. For the first time, we present evidence of a longrange order (LRO) in Er 2 Sn 2 O 7 ( x = 2.0 ) below T N = 130 mK. It is revealed that the moment configuration corresponds to a PalmerChalker type with a value of the magnetic moment significantly renormalized compared to x = 0 . We discuss our results in the framework of a possible quantum phase transition occurring close to x = 1.7 .

Determining the vortex tilt relative to a superconductor surface Phys. Rev. B (IF 3.836) Pub Date : 20171120
V. G. Kogan and J. R. KirtleyIt is of interest to determine the exit angle of a vortex from a superconductor surface, since this affects the intervortex interactions and their consequences. Two ways to determine this angle are to image the vortex magnetic fields above the surface, or the vortex core shape at the surface. In this work we evaluate the field h ( x , y , z ) above a flat superconducting surface x , y and the currents J ( x , y ) at that surface for a straight vortex tilted relative to the normal to the surface, for both the isotropic and anisotropic cases. In principle, these results can be used to determine the vortex exit tilt angle from analyses of magnetic field imaging or density of states data.

Unconventional superconductivity and an ambientpressure magnetic quantum critical point in singlecrystalLaNiC2 Phys. Rev. B (IF 3.836) Pub Date : 20171120
J. F. Landaeta, D. Subero, P. Machado, F. Honda, and I. BonaldeSuperconductivity in noncentrosymmetric LaNiC 2 is expected to be induced by electronphonon interactions due to its lack of magnetic instabilities. The nonBardeenCooperSchrieffer (BCS) behaviors found in this material call into question the longstanding idea that relates unconventional superconductivity with magnetic interactions. Here we report magnetic penetrationdepth measurements in a highpurity single crystal of LaNiC 2 at pressures up to 2.5 GPa and temperatures down to 0.04 K. At ambient pressure and below 0.5 T c the penetration depth goes as T 4 for the inplane and T 2 for the outofplane component, firmly implying the existence of point nodes in the energy gap and the unconventional character of this superconductor. The present study also provides evidence of magnetism in LaNiC 2 by unraveling a pressureinduced antiferromagnetic phase inside the superconducting state at temperatures below 0.5 K, with a quantum critical point around ambient pressure. The results presented here maintain a solid base for the notion that unconventional superconductivity only arises near magnetic order or fluctuations.

Thickness and angular dependence of the magnetocurrent of hot electrons in a magnetic tunnel transistor with crossed anisotropies Phys. Rev. B (IF 3.836) Pub Date : 20171120
C. Vautrin, D. Lacour, G. Sala, Y. Lu, F. Montaigne, and M. HehnWe have studied the thickness and angular dependence of the magnetocurrent of hot electrons in a magnetic tunnel transistor (MTT) with crossed magnetic anisotropies. In a first step, we show that the magnetocurrent increases with ferromagnetic layer thickness as for MTTs with collinear magnetic configurations. The maximum magnetocurrent value is obtained to be 85%, which is close to the theoretical maximum value of 100% for MTTs with crossed magnetic configurations. In a second step, we demonstrate that we are able to reproduce both current vs field direction and current vs field intensity measurements in a framework taking into account a reduced number of magnetic parameters and a simple cosine dependence of the hotelectron current on the angle between magnetizations.

Magnetization, specific heat, and thermal conductivity of hexagonalErMnO3single crystals Phys. Rev. B (IF 3.836) Pub Date : 20171120
J. D. Song, C. Fan, Z. Y. Zhao, F. B. Zhang, J. Y. Zhao, X. G. Liu, X. Zhao, Y. J. Liu, J. F. Wang, and X. F. SunWe report a study of magnetism and magnetic transitions of hexagonal ErMnO 3 single crystals by magnetization, specific heat, and heat transport measurements. Magnetization data show that the c axis magnetic field induces three magnetic transitions at 0.8, 12, and 28 T. The specific heat shows a peak at 2.2 K, which is due to a magnetic transition of Er 3 + moments. For low T thermal conductivity ( κ ) , a clear diplike feature appears in the κ ( H ) isotherm at 1–1.25 T for H ∥ a b , while in the case of H ∥ c , a steplike increase is observed at 0.5–0.8 T. The transition fields in κ ( H ) are in good agreement with those obtained from magnetization, and the anomaly of κ can be understood by a spinphonon scattering scenario. The natures of magnetic structures and corresponding fieldinduced transitions at low temperatures are discussed.

Spin excitations and quantum criticality in the quasionedimensional Isinglike ferromagnetCoCl2·2D2Oin a transverse field Phys. Rev. B (IF 3.836) Pub Date : 20171120
J. Larsen, T. K. Schäffer, U. B. Hansen, S. L. Holm, S. R. Ahl, R. ToftPetersen, J. Taylor, G. Ehlers, J. Jensen, H. M. Rønnow, K. Lefmann, and N. B. ChristensenWe present experimental evidence for a quantum phase transition in the easyaxis S = 3 / 2 anisotropic quasionedimensional ferromagnet CoCl 2 · 2 D 2 O in a transverse field. Elastic neutron scattering shows that the magnetic order parameter vanishes at a transverse critical field μ 0 H c = 16.05 (4) T, while inelastic neutron scattering shows that the gap in the magnetic excitation spectrum vanishes at the same field value, and reopens for H > H c . The field dependence of the order parameter and the gap are well described by critical exponents β = 0.45 ± 0.09 and z ν close to 1 / 2 , implying that the quantum phase transition in CoCl 2 · 2 D 2 O differs significantly from the textbook version of a S = 1 / 2 Ising chain in a transverse field. We attribute the difference to weak but finite threedimensionality of the magnetic interactions.

Disorderinduced topological phase transitions on Lieb lattices Phys. Rev. B (IF 3.836) Pub Date : 20171117
Rui Chen, DongHui Xu, and Bin ZhouMotivated by the very recent experimental realization of electronic Lieb lattices and research interest on topological states of matter, we study the topological phase transitions driven by Andersontype disorder on spinorbit coupled Lieb lattices in the presence of spinindependent and dependent staggered potentials. By combining the recursive Green'sfunction and selfconsistent Born approximation methods, we found that both timereversalinvariant and timereversalsymmetrybroken spinorbit coupled Lieb lattice systems can host the disorderinduced gapful topological phases, including the quantum spin Hall insulator (QSHI) and quantum anomalous Hall insulator (QAHI) phases. For the timereversalinvariant case, the disorder induces a topological phase transition directly from a normal insulator (NI) to the QSHI, while for the timereversalsymmetrybroken case, the disorder can induce either a QAHIQSHI phase transition or a NIQAHIQSHI phase transition, depending on the initial state of the system. Remarkably, the timereversalsymmetrybroken QSHI phase can be induced by Andersontype disorder on the spinorbit coupled Lieb lattices without timereversal symmetry.

Halfmetal phases in a quantum wire with modulated spinorbit interaction Phys. Rev. B (IF 3.836) Pub Date : 20171117
D. C. Cabra, G. L. Rossini, A. Ferraz, G. I. Japaridze, and H. JohannessonWe propose a spin filter device based on the interplay of a modulated spinorbit interaction and a uniform external magnetic field acting on a quantum wire. Halfmetal phases, where electrons with only a selected spin polarization exhibit ballistic conductance, can be tuned by varying the magnetic field. These halfmetal phases are proven to be robust against electronelectron repulsive interactions. Our results arise from a combination of explicit band diagonalization, bosonization techniques, and extensive density matrix renormalization group computations.

Voltagedependent cluster expansion for electrified solidliquid interfaces: Application to the electrochemical deposition of transition metals Phys. Rev. B (IF 3.836) Pub Date : 20171117
Stephen E. Weitzner and Ismaila DaboThe detailed atomistic modeling of electrochemically deposited metal monolayers is challenging due to the complex structure of the metalsolution interface and the critical effects of surface electrification during electrode polarization. Accurate models of interfacial electrochemical equilibria are further challenged by the need to include entropic effects to obtain accurate surface chemical potentials. We present an embedded quantumcontinuum model of the interfacial environment that addresses each of these challenges and study the underpotential deposition of silver on the gold (100) surface. We leverage these results to parametrize a cluster expansion of the electrified interface and show through grand canonical Monte Carlo calculations the crucial need to account for variations in the interfacial dipole when modeling electrodeposited metals under finitetemperature electrochemical conditions.

Critical divergence of the symmetric (A1g) nonlinear elastoresistance near the nematic transition in an ironbased superconductor Phys. Rev. B (IF 3.836) Pub Date : 20171117
J. C. Palmstrom, A. T. Hristov, S. A. Kivelson, J.H. Chu, and I. R. FisherWe report the observation of a nonlinear elastoresistivity response for the prototypical underdoped iron pnictide Ba ( Fe 0.975 Co 0.025 ) 2 As 2 . Our measurements reveal a large quadratic term in the isotropic ( A 1 g ) electronic response that was produced by a purely shear ( B 2 g ) strain. The divergence of this quantity upon cooling towards the structural phase transition reflects the temperature dependence of the nematic susceptibility. This observation shows that nematic fluctuations play a significant role in determining even the isotropic properties of this family of compounds.

Calibration of the finestructure constant of graphene by timedependent densityfunctional theory Phys. Rev. B (IF 3.836) Pub Date : 20171117
A. Sindona, M. Pisarra, C. Vacacela Gomez, P. Riccardi, G. Falcone, and S. BellucciOne of the amazing properties of graphene is the ultrarelativistic behavior of its loosely bound electrons, mimicking massless fermions that move with a constant velocity, inversely proportional to a finestructure constant α g of the order of unity. The effective interaction between these quasiparticles is, however, better controlled by the coupling parameter α g * = α g / ε , which accounts for the dynamic screening due to the complex permittivity ε of the manyvalence electron system. This concept was introduced in a couple of previous studies [Reed et al., Science 330, 805 (2010) and Gan et al., Phys. Rev. B 93, 195150 (2016)], where inelastic xray scattering measurements on crystal graphite were converted into an experimentally derived form of α g * for graphene, over an energymomentum region on the eV Å − 1 scale. Here, an accurate theoretical framework is provided for α g * , using timedependent densityfunctional theory in the randomphase approximation, with a cutoff in the interaction between excited electrons in graphene, which translates to an effective interlayer interaction in graphite. The predictions of the approach are in excellent agreement with the abovementioned measurements, suggesting a calibration method to substantially improve the experimental derivation of α g * , which tends to a static limiting value of ∼ 0.14 . Thus, the ab initio calibration procedure outlined demonstrates the accuracy of perturbation expansion treatments for the twodimensional gas of massless Dirac fermions in graphene, in parallel with quantum electrodynamics.

Thermoelectric power factor of nanocomposite materials from twodimensional quantum transport simulations Phys. Rev. B (IF 3.836) Pub Date : 20171117
Samuel Foster, Mischa Thesberg, and Neophytos NeophytouNanocomposites are promising candidates for the next generation of thermoelectric materials since they exhibit extremely low thermal conductivities as a result of phonon scattering on the boundaries of the various material phases. The nanoinclusions, however, should not degrade the thermoelectric power factor, and ideally should increase it, so that benefits to the ZT figure of merit can be achieved. In this work we employ the nonequilibrium Green's function quantum transport method to calculate the electronic and thermoelectric coefficients of materials embedded with nanoinclusions. For computational effectiveness we consider twodimensional nanoribbon geometries, however, the method includes the details of geometry, electronphonon interactions, quantization, tunneling, and the ballistic to diffusive nature of transport, all combined in a unified approach. This makes it a convenient and accurate way to understand electronic and thermoelectric transport in nanomaterials, beyond semiclassical approximations, and beyond approximations that deal with the complexities of the geometry. We show that the presence of nanoinclusions within a matrix material offers opportunities for only weak energy filtering, significantly lower in comparison to superlattices, and thus only moderate power factor improvements. However, we describe how such nanocomposites can be optimized to limit degradation in the thermoelectric power factor and elaborate on the conditions that achieve the aforementioned mild improvements. Importantly, we show that under certain conditions, the power factor is independent of the density of nanoinclusions, meaning that materials with large nanoinclusion densities which provide very low thermal conductivities can also retain large power factors and result in large ZT figures of merit.

Fast pulse sequences for dynamically corrected gates in singlettriplet qubits Phys. Rev. B (IF 3.836) Pub Date : 20171117
Robert E. Throckmorton, Chengxian Zhang, XuChen Yang, Xin Wang, Edwin Barnes, and S. Das SarmaWe present a set of experimentally feasible pulse sequences that implement any singlequbit gate on a singlettriplet spin qubit and demonstrate that these new sequences are up to three times faster than existing sequences in the literature. We show that these sequences can be extended to incorporate builtin dynamical error correction, yielding gates that are robust to both charge and magnetic field noise and up to twice as fast as previous dynamically corrected gate schemes. We present a thorough comparison of the performance of our new sequences with that of several existing ones using randomized benchmarking, considering both quasistatic and 1 / f α noise models. We provide our results both as a function of evolution time and as a function of the number of gates, which respectively yield both an effective coherence time and an estimate of the number of gates that can be performed within this coherence time. We determine which set of pulse sequences gives the best results for a wide range of noise strengths and power spectra. Overall, we find that the traditional, slower sequences perform best when there is no field noise or when the noise contains significant highfrequency components; otherwise, our new, fast sequences exhibit the best performance.

Proximity effect model of ultranarrow NbN strips Phys. Rev. B (IF 3.836) Pub Date : 20171117
I. Charaev, T. Silbernagel, B. Bachowsky, A. Kuzmin, S. Doerner, K. Ilin, A. Semenov, D. Roditchev, D. Yu. Vodolazov, and M. SiegelWe show that narrow superconducting strips in superconducting (S) and normal (N) states are universally described by the model presenting them as lateral NSN proximity systems in which the superconducting central band is sandwiched between damaged edge bands with suppressed superconductivity. The width of the superconducting band was experimentally determined from the value of magnetic field at which the band transits from the Meissner state to the static vortex state. Systematic experimental study of 4.9nmthick NbN strips with widths in the interval from 50 nm to 20 μm, which are all smaller than the Pearl's length, demonstrates gradual evolution of the temperature dependence of the critical current with the change of the strip width.

Resonant inelastic xray scattering probes the electronphonon coupling in the spin liquidκ(BEDTTTF)2Cu2(CN)3 Phys. Rev. B (IF 3.836) Pub Date : 20171117
V. Ilakovac, S. Carniato, P. FouryLeylekian, S. Tomić, J.P. Pouget, P. Lazić, Y. Joly, K. Miyagawa, K. Kanoda, and A. NicolaouResonant inelastic xray scattering at the N K edge reveals clearly resolved harmonics of the anion plane vibrations in the κ (BEDT TTF ) 2 Cu 2 ( CN ) 3 spinliquid insulator. Tuning the incoming light energy at the K edge of two distinct N sites permits us to excite different sets of phonon modes. The cyanide (CN) stretching mode is selected at the edge of the ordered N sites which are more strongly connected to the bis(ethylenedithio)tetrathiafulvalene (BEDTTTF) molecules, while positionally disordered N sites show multimode excitation. Combining measurements with calculations on an anion plane cluster permits us to estimate the sitedependent electronphonon coupling of the modes related to nitrogen excitation.

Towards accurate models for amorphous GeTe: Crucial effect of dispersive van der Waals corrections on the structural properties involved in the phasechange mechanism Phys. Rev. B (IF 3.836) Pub Date : 20171117
M. Micoulaut, A. Piarristeguy, H. FloresRuiz, and A. PradelThe effect of van der Waals dispersion correction in combination with density functional theory is investigated on a canonical amorphous phasechange material. Density functional theory (DFT), using the generalized gradient approximation, usually fails to reproduce the structure of amorphous tellurides, which manifests by an overestimation of the interatomic bond distances, and particularly the GeTe one involved in local geometries (tetrahedral or defect octahedral). Here, we take into account dispersion forces in a semiempirical way and apply such DFT simulations to amorphous GeTe. We obtain a substantial improvement of the simulated structure factor and paircorrelation function, which now reproduce the experimental counterparts with an unprecedented accuracy, including on a recent partial contribution from anomalous xray scattering and from xray absorption. A detailed analysis of the corresponding structures indicates that the dispersion correction reduces the GeTe bond length, increases the fraction of tetrahedral germanium, and reduces the presence of heteropolar socalled fourfold ABAB rings. Given that these structural features have been stressed to be central for the understanding of the phasechange mechanism, the present results challenge our current understanding of the crystal to amorphous transformation at play.

Superconductivity in engineered twodimensional electron gases Phys. Rev. B (IF 3.836) Pub Date : 20171117
Andrey V. Chubukov and Steven A. KivelsonWe consider KohnLuttinger mechanism for superconductivity in a twodimensional electron gas confined to a narrow well between two grounded metallic planes with two occupied subbands with Fermi momenta k F L > k F S . On the basis of a perturbative analysis, we conclude that non s wave superconductivity emerges even when the bands are parabolic. We analyze the conditions that maximize T c as a function of the distance to the metallic planes, the ratio k F L / k F S , and r s , which measures the strength of Coulomb correlations. The largest attraction is in p wave and d wave channels, of which p wave is typically the strongest. For r s = O ( 1 ) we estimate that the dimensionless coupling λ ≈ 10 − 1 , but it likely continues increasing for larger r s (where we lose theoretical control).

One dimensionalization in the spin1 Heisenberg model on the anisotropic triangular lattice Phys. Rev. B (IF 3.836) Pub Date : 20171117
M. G. Gonzalez, E. A. Ghioldi, C. J. Gazza, L. O. Manuel, and A. E. TrumperWe investigate the effect of dimensional crossover in the ground state of the antiferromagnetic spin1 Heisenberg model on the anisotropic triangular lattice that interpolates between the regime of weakly coupled Haldane chains ( J ′ ≪ J ) and the isotropic triangular lattice ( J ′ = J ) . We use the densitymatrix renormalization group (DMRG) and Schwinger boson theory performed at the Gaussian correction level above the saddlepoint solution. Our DMRG results show an abrupt transition between decoupled spin chains and the spirally ordered regime at ( J ′ / J ) c ∼ 0.42 , signaled by the sudden closing of the spin gap. Coming from the magnetically ordered side, the computation of the spin stiffness within Schwinger boson theory predicts the instability of the spiral magnetic order toward a magnetically disordered phase with onedimensional features at ( J ′ / J ) c ∼ 0.43 . The agreement of these complementary methods, along with the strong difference found between the intra and the interchain DMRG short spinspin correlations for sufficiently large values of the interchain coupling, suggests that the interplay between the quantum fluctuations and the dimensional crossover effects gives rise to the onedimensionalization phenomenon in this frustrated spin1 Hamiltonian.

Green's function formalism for spin transport in metalinsulatormetal heterostructures Phys. Rev. B (IF 3.836) Pub Date : 20171117
Jiansen Zheng, Scott Bender, Jogundas Armaitis, Roberto E. Troncoso, and Rembert A. DuineWe develop a Green's function formalism for spin transport through heterostructures that contain metallic leads and insulating ferromagnets. While this formalism in principle allows for the inclusion of various magnonic interactions, we focus on Gilbert damping. As an application, we consider ballistic spin transport by exchange magnons in a metalinsulatormetal heterostructure with and without disorder. For the former case, we show that the interplay between disorder and Gilbert damping leads to spin current fluctuations. For the case without disorder, we obtain the dependence of the transmitted spin current on the thickness of the ferromagnet. Moreover, we show that the results of the Green's function formalism agree in the clean and continuum limit with those obtained from the linearized stochastic LandauLifshitzGilbert equation. The developed Green's function formalism is a natural starting point for numerical studies of magnon transport in heterostructures that contain normal metals and magnetic insulators.

Evolution of magnetic phases inSmCrO3: A neutron diffraction and magnetometric study Phys. Rev. B (IF 3.836) Pub Date : 20171117
Malvika Tripathi, R. J. Choudhary, D. M. Phase, T. Chatterji, and H. E. FischerThe classical belief about the mechanism of spin reorientation phase transition (SRPT) and groundstate magnetic structure in SmCrO 3 has become intriguing because of inconsistent bulk magnetization observations. The presence of highly neutronabsorbing Sm atom has so far evaded the determination of microscopic magnetic structure. In the present report, we have utilized very highenergy “hot neutrons” to overcome the Sm absorption and to determine the thermal evolution of magnetic configurations. Unambiguously, three distinct phases are observed: the uncompensated canted antiferromagnetic structure Γ 4 ( G x , A y , F z ; F z R ) occurring below the Néel temperature ( T N = 191 K), the collinear antiferromagnetic structure Γ 1 ( A x , G y , C z ; C z R ) occurring below 10 K, and a nonequilibrium configuration with cooccurring Γ 1 and Γ 4 phases in the neighborhood of the SRPT (10 K ≤ T ≤ 40 K). In differing to the earlier predictions, we divulge the SRPT to be a discontinuous transition where chromium spins switch from the a − b crystallographic plane to the b − c crystallographic plane in a discrete manner with no allowed intermediate configuration. The canting angle of chromium ions in the a − b plane is unusually not a thermal constant, rather it is empirically discerned to follow exponential behavior. The competition between magnetocrystalline anisotropy and free energy derived by isotropic and antisymmetric exchange interactions between different pairs of magnetic ions is observed to govern the mechanism of SRPT.

Firstprinciplesbased LandauDevonshire potential forBiFeO3 Phys. Rev. B (IF 3.836) Pub Date : 20171117
P. Marton, A. Klíč, M. Paściak, and J. HlinkaThe work describes a firstprinciplesbased computational strategy for studying structural phase transitions, and in particular, for determination of the socalled LandauDevonshire potential—the classical zerotemperature limit of the Gibbs energy, expanded in terms of order parameters. It exploits the configuration space attached to the eigenvectors of the modes frozen in the ground state, rather than the space spanned by the unstable modes of the highsymmetry phase, as done usually. This allows us to carefully probe the part of the energy surface in the vicinity of the ground state, which is most relevant for the properties of the ordered phase. We apply this procedure to BiFeO 3 and perform ab initio calculations in order to determine potential energy contributions associated with strain, polarization, and oxygen octahedra tilt degrees of freedom, compatible with its twoformula unit cell periodic boundary conditions.

Photomagnetoelectric and magnetophotovoltaic effects in multiferroicBiFeO3 Phys. Rev. B (IF 3.836) Pub Date : 20171116
Bruno Mettout and Pierre TolédanoA polarized light beam modifies the equilibrium tensors associated with any measurable property of a crystal. The lightinduced linear magnetoelectric susceptibility and electric current density of bismuth ferrite (BFO) are investigated theoretically using their expansion in Wigner spherical functions. Under illumination, the interplay between magnetoelectric and photovoltaic properties yields the emergence in the paramagnetic and multiferroic phases of BFO of linear photomagnetoelectric tensor components changing sign in domains with opposite electric polarization or magnetization, and to magnetophotocurrents changing sense in opposite ferroelectric and magnetic domains.

Hall effect in cuprates with an incommensurate collinear spindensity wave Phys. Rev. B (IF 3.836) Pub Date : 20171116
M. Charlebois, S. Verret, A. Foley, O. Simard, D. Sénéchal, and A.M. S. TremblayThe presence of incommensurate spiral spindensity waves (SDW) has been proposed to explain the p (hole doping) to 1 + p jump measured in the Hall number n H at a doping p * . Here we explore incommensurate collinear SDW as another possible explanation of this phenomenon, distinct from the incommensurate spiral SDW proposal. We examine the effect of different SDW strengths and wave vectors, and we find that the n H ∼ p behavior is hardly reproduced at low doping. Furthermore, the calculated n H and Fermi surfaces give characteristic features that should be observed; thus, the lack of these features in experiment suggests that the incommensurate collinear SDW is unlikely to be a good candidate to explain the n H ∼ p observed in the pseudogap regime.

Quantized charge transport in chiral Majorana edge modes Phys. Rev. B (IF 3.836) Pub Date : 20171116
Stephan Rachel, Eric Mascot, Sagen Cocklin, Matthias Vojta, and Dirk K. Morr 
Nonnecessity of band inversion process in twodimensional topological insulators for bulk gapless states and topological phase transitions Phys. Rev. B (IF 3.836) Pub Date : 20171116
Wenjie Xi (奚文杰) and Wei Ku (顧威)In commonly employed models for twodimensional (2D) topological insulators, bulk gapless states are well known to form at the band inversion points where the degeneracy of the states is protected by symmetries. It is thus sometimes quite tempting to consider this feature, the occurrence of gapless states, a result of the band inversion process under protection of the symmetries. Similarly, the band inversion process might even be perceived as necessary to induce 2D topological phase transitions. To clarify these misleading perspectives, we propose a simple model with a flexible Chern number to demonstrate that the bulk gapless states emerge at the phase boundary of topological phase transitions, despite the absence of a band inversion process. Furthermore, the bulk gapless states do not need to occur at the special k points protected by symmetries. Given the significance of these fundamental conceptual issues and their widespread influence, our clarification should generate strong general interests and significant impacts. Furthermore, the simplicity and flexibility of our general model with an arbitrary Chern number should prove useful in a wide range of future studies of topological states of matter.

Erratum: Reliability of Raman measurements of thermal conductivity of singlelayer graphene due to selective electronphonon coupling: A firstprinciples study [Phys. Rev. B93, 125432 (2016)] Phys. Rev. B (IF 3.836) Pub Date : 20171116
Ajit K. Vallabhaneni, Dhruv Singh, Hua Bao, Jayathi Murthy, and Xiulin RuanDOI:https://doi.org/10.1103/PhysRevB.96.199903

Geometrical phase shift in Friedel oscillations Phys. Rev. B (IF 3.836) Pub Date : 20171116
C. Dutreix and P. DelplaceThis work addresses the problem of elastic scattering on a localized impurity in a onedimensional crystal with sublattice degrees of freedom. The impurity yields longrange interferences in the local density of states known as Friedel oscillations. Here we show that the internal degrees of freedom of Bloch waves are responsible for a geometrical phase shift in Friedel oscillations. The Fourier transform of the energyresolved interference pattern reveals a topological property of this phase shift, which is intrinsically related to a wavefunction topological property (Zak phase) in the absence of impurity. As a result, Friedel oscillations in the local density of states can be regarded as a probe of wave topological properties in a broad class of classical and quantum systems, such as acoustic and photonic crystals, ultracold atomic gases in optical lattices, and electronic compounds.

Currentinduced spin polarization in InGaAs and GaAs epilayers with varying doping densities Phys. Rev. B (IF 3.836) Pub Date : 20171116
M. LuengoKovac, S. Huang, D. Del Gaudio, J. Occena, R. S. Goldman, R. Raimondi, and V. SihThe currentinduced spin polarization and momentumdependent spinorbit field were measured in In x Ga 1 − x As epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, currentinduced spin polarization was detected in GaAs epilayers despite the absence of measurable spinorbit fields, indicating that the extrinsic contributions to the spinpolarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spinorbit coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spinorbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the currentinduced spin polarization.

Role of the transition state in muon implantation Phys. Rev. B (IF 3.836) Pub Date : 20171116
R. C. Vilão, R. B. L. Vieira, H. V. Alberto, J. M. Gil, and A. WeidingerIn muonspinrotation experiments, positive muons are implanted in the material and come to rest in the unrelaxed host lattice. The formation of the final configuration requires a lattice relaxation which does not occur instantly. The present paper is concerned with the transition from the initial stopping state to the final muon configuration. We identify the often observed fast relaxing signal in muon experiments (e.g., in several oxides studied recently) with the transition state in this conversion process. This state is paramagnetic with a small hyperfine interaction (in the order of MHz) which fluctuates and averages to almost zero. Because of its apparent diamagnetic frequency behavior, the fast signal was in the past assigned to Mu + or Mu − . We present evidence that this state is actually paramagnetic. The model presented in this paper is of importance for the interpretation of past and future μ SR measurements.

Charge puddles in the bulk and on the surface of the topological insulatorBiSbTeSe2studied by scanning tunneling microscopy and optical spectroscopy Phys. Rev. B (IF 3.836) Pub Date : 20171116
T. Knispel, W. Jolie, N. Borgwardt, J. Lux, Zhiwei Wang, Yoichi Ando, A. Rosch, T. Michely, and M. Grüninger 
Bulk boundary correspondence and the existence of Majorana bound states on the edges of 2D topological superconductors Phys. Rev. B (IF 3.836) Pub Date : 20171116
Nicholas Sedlmayr, Vardan Kaladzhyan, Clément Dutreix, and Cristina BenaThe bulkboundary correspondence establishes a connection between the bulk topological index of an insulator or superconductor, and the number of topologically protected edge bands or states. For topological superconductors in two dimensions, the first Chern number is related to the number of protected bands within the bulk energy gap, and is therefore assumed to give the number of Majorana band states in the system. Here we show that this is not necessarily the case. As an example, we consider a hexagonallattice topological superconductor based on a model of graphene with Rashba spinorbit coupling, proximityinduced s wave superconductivity, and a Zeeman magnetic field. We explore the full Chern number phase diagram of this model, extending what is already known about its parity. We then demonstrate that, despite the high Chern numbers that can be seen in some phases, these do not strictly always contain Majorana bound states.

Surface impedance and optimum surface resistance of a superconductor with an imperfect surface Phys. Rev. B (IF 3.836) Pub Date : 20171116
Alex Gurevich and Takayuki KuboWe calculate a lowfrequency surface impedance of a dirty, s wave superconductor with an imperfect surface incorporating either a thin layer with a reduced pairing constant or a thin, proximitycoupled normal layer. Such structures model realistic surfaces of superconducting materials which can contain oxide layers, absorbed impurities, or nonstoichiometric composition. We solved the Usadel equations selfconsistently and obtained spatial distributions of the order parameter and the quasiparticle density of states which then were used to calculate a lowfrequency surface resistance R s ( T ) and the magnetic penetration depth λ ( T ) as functions of temperature in the limit of local London electrodynamics. It is shown that the imperfect surface in a singleband s wave superconductor results in a nonexponential temperature dependence of Z ( T ) at T ≪ T c which can mimic the behavior of multiband or d wave superconductors. The imperfect surface and the broadening of the gap peaks in the quasiparticle density of states N ( ε ) in the bulk give rise to a weakly temperaturedependent residual surface resistance. We show that the surface resistance can be optimized and even reduced below its value for an ideal surface by engineering N ( ε ) at the surface using pairbreaking mechanisms, particularly by incorporating a small density of magnetic impurities or by tuning the thickness and conductivity of the normal layer and its contact resistance. The results of this work address the limit of R s in superconductors at T ≪ T c , and the ways of engineering the optimal density of states by surface nanostructuring and impurities to reduce losses in superconducting microresonators, thinfilm strip lines, and radiofrequency cavities for particle accelerators.

Boundarydriven Heisenberg chain in the longrange interacting regime: Robustness against farfromequilibrium effects Phys. Rev. B (IF 3.836) Pub Date : 20171116
Leon Droenner and Alexander CarmeleWe investigate the Heisenberg X X Z chain with longrange interactions in the Z dimension. By applying two magnetic boundary reservoirs, we drive the system out of equilibrium and induce a nonzero steadystate current. The longrange coupled chain shows nearly ballistic transport and linear response for all potential differences of the external reservoirs. In contrast, the common isotropic nearestneighbor coupling shows negative differential conductivity and a transition from diffusive to subdiffusive transport for a farfromequilibrium driving. Adding disorder, the change in the transport for nearestneighbor coupling is therefore highly dependent on the driving. We find for the disordered longrange coupled X X Z chain, any change in the transport behavior is independent of the potential difference and the coupling strengths of the external reservoirs.

Highresolution resonant inelastic extreme ultraviolet scattering from orbital and spin excitations in a Heisenberg antiferromagnet Phys. Rev. B (IF 3.836) Pub Date : 20171116
Antonio Caretta, Martina Dell'Angela, YiDe Chuang, Alexandra M. Kalashnikova, Roman V. Pisarev, Davide Bossini, Florian Hieke, Wilfried Wurth, Barbara Casarin, Roberta Ciprian, Fulvio Parmigiani, Surge Wexler, L. Andrew Wray, and Marco MalvestutoWe report a highresolution resonant inelastic extreme ultraviolet (EUV) scattering study of the quantum Heisenberg antiferromagnet KCoF 3 . By tuning the EUV photon energy to the cobalt M 23 edge, a complete set of lowenergy 3 d spinorbital excitations is revealed. These lowlying electronic excitations are modeled using an extended multipletbased meanfield calculation to identify the roles of lattice and magnetic degrees of freedom in modifying the resonant inelastic xray scattering (RIXS) spectral line shape. We have demonstrated that the temperature dependence of RIXS features upon the antiferromagnetic ordering transition enables us to probe the energetics of shortrange spin correlations in this material.

Raman scattering study of the tetragonal magnetic phase inSr1−xNaxFe2As2: Structural symmetry and electronic gap Phys. Rev. B (IF 3.836) Pub Date : 20171116
Li Yue, Xiao Ren, Tingting Han, Jianqing Guo, Zhicheng Wu, Yan Zhang, and Yuan LiWe use inelastic light scattering to study Sr 1 − x Na x Fe 2 As 2 ( x ≈ 0.34 ), which exhibits a robust tetragonal magnetic phase that restores the fourfold rotation symmetry inside the orthorhombic magnetic phase. With cooling, we observe splitting and recombination of an E g phonon peak upon entering the orthorhombic and tetragonal magnetic phases, respectively, consistent with the reentrant phase behavior. Our electronic Raman data reveal a pronounced feature that is clearly associated with the tetragonal magnetic phase, suggesting the opening of a different electronic gap. The energy of this gap is substantially smaller than the gap observed in the orthorhombic magnetic phase, and the two gaps compete only weakly for spectral weight. These observations are consistent with the notion that the reentrant phase behavior is driven by spinorbit interactions, which seem to dictate the manifestation of magnetism in Febased superconductors. No phonon back folding can be detected above the noise level, which implies that any lattice translation symmetry breaking in the tetragonal magnetic phase must be very weak.

Nearly isotropic superconductivity in the layered Weyl semimetalWTe2at 98.5 kbar Phys. Rev. B (IF 3.836) Pub Date : 20171116
Yuk Tai Chan, P. L. Alireza, K. Y. Yip, Q. Niu, K. T. Lai, and Swee K. GohThe layered transition metal dichalcogenide WTe 2 has recently attracted significant attention due to the discovery of an extremely large magnetoresistance, a predicted typeII Weyl semimetallic state, and a pressureinduced superconducting state. By a careful measurement of the superconducting upper critical fields as a function of the magnetic field angle at a pressure as high as 98.5 kbar, we provide the first detailed examination of the dimensionality of the superconducting condensate in WTe 2 . Despite the layered crystal structure, the upper critical field exhibits a negligible field anisotropy. The angular dependence of the upper critical field can be satisfactorily described by the anisotropic mass model from 2.2 K ( T / T c ∼ 0.67 ) to 0.03 K ( T / T c ∼ 0.01 ), with a practically identical anisotropy factor γ ∼ 1.7 . The temperature dependence of the upper critical field, determined for both H ⊥ a b and H ∥ a b , can be understood by a conventional orbital depairing mechanism. A comparison of the upper critical fields along the two orthogonal field directions results in the same value of γ ∼ 1.7 , leading to a temperatureindependent anisotropy factor from near T c to < 0.01 T c . Our findings thus identify WTe 2 as a nearly isotropic superconductor, with an anisotropy factor among one of the lowest known in superconducting transition metal dichalcogenides.

Spin excitation anisotropy in the optimally isovalentdoped superconductorBaFe2(As0.7P0.3)2 Phys. Rev. B (IF 3.836) Pub Date : 20171116
Ding Hu, Wenliang Zhang, Yuan Wei, Bertrand Roessli, Markos Skoulatos, Louis Pierre Regnault, Genfu Chen, Yu Song, Huiqian Luo, Shiliang Li, and Pengcheng DaiWe use neutron polarization analysis to study spin excitation anisotropy in the optimally isovalentdoped superconductor BaFe 2 ( As 0.7 P 0.3 ) 2 ( T c = 30 K). Different from optimally hole and electrondoped BaFe 2 As 2 , where there is a clear spin excitation anisotropy in the paramagnetic tetragonal state well above T c , we find no spin excitation anisotropy for energies above 2 meV in the normal state of BaFe 2 ( As 0.7 P 0.3 ) 2 . Upon entering the superconducting state, significant spin excitation anisotropy develops at the antiferromagnetic (AF) zone center Q AF = ( 1 , 0 , L = odd ) , while the magnetic spectrum is isotropic at the zone boundary Q = ( 1 , 0 , L = even ) . By comparing the temperature, wave vector, and polarization dependence of the spin excitation anisotropy in BaFe 2 ( As 0.7 P 0.3 ) 2 and holedoped Ba 0.67 K 0.33 Fe 2 As 2 ( T c = 38 K), we conclude that such anisotropy arises from spinorbit coupling and is associated with the nearby AF order and superconductivity.

Singleparameter scaling and maximum entropy inside disordered onedimensional systems: Theory and experiment Phys. Rev. B (IF 3.836) Pub Date : 20171116
Xiaojun Cheng, Xujun Ma, Miztli Yépez, Azriel Z. Genack, and Pier A. MelloThe singleparameter scaling hypothesis relating the average and variance of the logarithm of the conductance is a pillar of the theory of electronic transport. We use a maximumentropy ansatz to explore the logarithm of the particle, or energy density ln W ( x ) at a depth x into a random onedimensional system. Singleparameter scaling would be the special case in which x = L (the system length). We find the result, confirmed in microwave measurements and computer simulations, that the average of ln W ( x ) is independent of L and equal to − x / ℓ , with ℓ the mean free path. At the beginning of the sample, var [ ln W ( x ) ] rises linearly with x and is also independent of L , with a sublinear increase and then a drop near the sample output. At x = L we find a correction to the value of var [ ln T ] predicted by singleparameter scaling.

Publisher's Note: Domainwidth model for perpendicularly magnetized systems with DzyaloshinskiiMoriya interaction [Phys. Rev. B96, 144408 (2017)] Phys. Rev. B (IF 3.836) Pub Date : 20171116
T. N. G. Meier, M. Kronseder, and C. H. BackDOI:https://doi.org/10.1103/PhysRevB.96.179902

Band structure and Fermi surfaces of the reentrant ferromagnetic superconductorEu(Fe0.86Ir0.14)2As2 Phys. Rev. B (IF 3.836) Pub Date : 20171116
S. Xing, J. Mansart, V. Brouet, M. Sicot, Y. FagotRevurat, B. Kierren, P. Le Fèvre, F. Bertran, J. E. Rault, U. B. Paramanik, Z. Hossain, A. Chainani, and D. MalterreThe electronic structure of the reentrant superconductor Eu ( Fe 0.86 Ir 0.14 ) 2 As 2 ( T c = 22 K) with coexisting ferromagnetic order ( T M = 18 K) is investigated using angleresolved photoemission spectroscopy and scanning tunneling spectroscopy. We study the inplane and outofplane band dispersions and Fermi surface (FS) of Eu ( Fe 0.86 Ir 0.14 ) 2 As 2 . The near E F Fe 3 d derived band dispersions near the Γ and X highsymmetry points show changes due to Ir substitution, but the FS topology is preserved. From momentumdependent measurements of the superconducting gap measured at T = 5 K, we estimate an essentially isotropic s wave gap ( Δ ∼ 5.25 ± 0.25 meV), indicative of strongcoupling superconductivity with 2 Δ / k B T c ≃ 5.8 . The gap gets closed at temperatures T ≥ 10 K, and this is attributed to the resistive phase which sets in at T M = 18 K due to the Eu 2 + derived magnetic order. The modification of the FS with Ir substitution clearly indicates an effective hole doping with respect to the parent compound.

Emergent exotic superconductivity in artificially engineered tricolor Kondo superlattices Phys. Rev. B (IF 3.836) Pub Date : 20171116
M. Naritsuka, T. Ishii, S. Miyake, Y. Tokiwa, R. Toda, M. Shimozawa, T. Terashima, T. Shibauchi, Y. Matsuda, and Y. KasaharaIn the quest for exotic superconducting pairing states, the Rashba effect, which lifts the electronspin degeneracy as a consequence of strong spinorbit interaction (SOI) under broken inversion symmetry, has attracted considerable interest. Here, to introduce the Rashba effect into twodimensional (2D) strongly correlated electron systems, we fabricate noncentrosymmetric (tricolor) superlattices composed of three kinds of f electron compounds with atomic thickness; d wave heavy fermion superconductor CeCoIn 5 sandwiched by two different nonmagnetic metals, YbCoIn 5 and YbRhIn 5 . We find that the Rashba SOIinduced global inversion symmetry breaking in these tricolor Kondo superlattices leads to profound changes in the superconducting properties of CeCoIn 5 , which are revealed by unusual temperature and angular dependencies of upper critical fields that are in marked contrast with the bulk CeCoIn 5 single crystals. We demonstrate that the Rashba effect incorporated into 2D CeCoIn 5 block layers is largely tunable by changing the layer thickness. Moreover, the temperature dependence of inplane upper critical field exhibits an anomalous upturn at low temperatures, which is attributed to a possible emergence of a helical or stripe superconducting phase. Our results demonstrate that the tricolor Kondo superlattices provide a new playground for exploring exotic superconducting states in the strongly correlated 2D electron systems with the Rashba effect.

Intrinsic ac anomalous Hall effect of nonsymmorphic chiral superconductors with an application toUPt3 Phys. Rev. B (IF 3.836) Pub Date : 20171116
Zhiqiang Wang, John Berlinsky, Gertrud Zwicknagl, and Catherine Kallin 
Spinwave propagation and spinpolarized electron transport in singlecrystal iron films Phys. Rev. B (IF 3.836) Pub Date : 20171116
O. Gladii, D. Halley, Y. Henry, and M. BailleulThe techniques of propagating spinwave spectroscopy and currentinduced spinwave Doppler shift are applied to a 20nmthick Fe/MgO(001) film. The magnetic parameters extracted from the position of the spinwave resonance peaks are very close to those tabulated for bulk iron. From the zerocurrent propagating wave forms, a group velocity of 4 km/s and an attenuation length of about 6 μ m are extracted for 1.6 μ m wavelength spin wave at 18 GHz. From the measured currentinduced spinwave Doppler shift, we extract a surprisingly high degree of spin polarization of the current of 83 % , which constitutes the main finding of this work. This set of results makes singlecrystalline iron a promising candidate for building devices utilizing highfrequency spin waves and spinpolarized currents.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.