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  • First-principles calculations of charge carrier mobility and conductivity in bulk semiconductors and two-dimensional materials
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2020-02-04
    Samuel Poncé, Wenbin Li, Sven Reichardt and Feliciano Giustino

    One of the fundamental properties of semiconductors is their ability to support highly tunable electric currents in the presence of electric fields or carrier concentration gradients. These properties are described by transport coefficients such as electron and hole mobilities. Over the last decades, our understanding of carrier mobilities has largely been shaped by experimental investigations and empirical models. Recently, advances in electronic structure methods for real materials have made it possible to study these properties with predictive accuracy and without resorting to empirical parameters. These new developments are unlocking exciting new opportunities, from exploring carrier transport in quantum matter to in silico designing new semiconductors with tailored transport properties. In this article, we review the most recent developments in the area of ab initio calculations of carrier mobilities of semiconductors. Our aim is threefold: to make this rapidl...

  • It is all about phases: ultrafast holographic photoelectron imaging
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2020-01-28
    C Figueira de Morisson Faria and A S Maxwell

    Photoelectron holography constitutes a powerful tool for the ultrafast imaging of matter, as it combines high electron currents with subfemtosecond resolution, and gives information about transition amplitudes and phase shifts. Similarly to light holography, it uses the phase difference between the probe and the reference waves associated with qualitatively different ionization events for the reconstruction of the target and for ascertaining any changes that may occur. These are major advantages over other attosecond imaging techniques, which require elaborate interferometric schemes in order to extract phase differences. For that reason, ultrafast photoelectron holography has experienced a huge growth in activity, which has led to a vast, but fragmented landscape. The present review is an organizational effort towards unifying this landscape. This includes a historic account in which a connection with laser-induced electron diffraction is established, a summary of the main holo...

  • Review on novel methods for lattice gauge theories
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2020-01-21
    Mari Carmen Bañuls and Krzysztof Cichy

    Formulating gauge theories on a lattice offers a genuinely non-perturbative way of studying quantum field theories, and has led to impressive achievements. In particular, it significantly deepened our understanding of quantum chromodynamics. Yet, some very relevant problems remain inherently challenging, such as real time evolution, or the presence of a chemical potential, cases in which Monte Carlo simulations are hindered by a sign problem. In the last few years, a number of possible alternatives have been put forward, based on quantum information ideas, which could potentially open the access to areas of research that have so far eluded more standard methods. They include tensor network calculations, quantum simulations with different physical platforms and quantum computations, and constitute nowadays a vibrant research area. Experts from different fields, including experimental and theoretical high energy physics, condensed matter, and quantum information, are turnin...

  • Optomechanics with levitated particles
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2020-01-16
    James Millen, Tania S Monteiro, Robert Pettit and A Nick Vamivakas

    Optomechanics is concerned with the use of light to control mechanical objects. As a field, it has been hugely successful in the production of precise and novel sensors, the development of low-dissipation nanomechanical devices, and the manipulation of quantum signals. Micro- and nano-particles levitated in optical fields act as nanoscale oscillators, making them excellent low-dissipation optomechanical objects, with minimal thermal contact to the environment when operating in vacuum. Levitated optomechanics is seen as the most promising route for studying high-mass quantum physics, with the promise of creating macroscopically separated superposition states at masses of 10 6 amu and above. Optical feedback, both using active monitoring or the passive interaction with an optical cavity, can be used to cool the centre-of-mass of levitated nanoparticles well below 1 mK, paving the way to operation in the quantum regime. In addition, trapped mesoscopic particles are the pa...

  • Hard x-ray spectroscopy and dynamics of isolated atoms and molecules: a review
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-12-17
    M N Piancastelli, T Marchenko, R Guillemin, L Journel, O Travnikova, I Ismail and M Simon

    We present here a review of the most significant recent achievements in the field of HAXPES (hard x-ray photoelectron spectroscopy) on isolated atoms and molecules, and related spectroscopies. The possibility of conducting hard x-ray photoexcitation and photoionization experiments under state-of-the art conditions in terms of photon and electron kinetic energy resolution has become available only in the last few years. HAXPES has then produced structural and dynamical information at the level of detail already reached in the VUV and soft-x-ray ranges. The much improved experimental conditions have allowed extending to the hard x-ray range some methods well established in soft x-ray spectroscopies. Investigations of electron and nuclear dynamics in the femtosecond (fs, 10 −15 s) and even attosecond (as, 10 −18 s) regime have become feasible. Complex relaxation phenomena following deep-core ionization can now be enlightened in great detail. Other phenomena like...

  • Holographic systems far from equilibrium: a review
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-12-04
    Hong Liu and Julian Sonner

    In this paper we give an overview of some recent progress in using holography to study various far-from-equilibrium condensed matter systems. Non-equilibrium problems are notoriously difficult to deal with, not to mention at strong coupling and when including quantum effects. Remarkably, using holographic duality one can describe and follow the real-time evolution of far-from-equilibrium systems, including those which are spatially inhomogeneous and anisotropic, by solving partial differential gravity equations. We sample developments in two broad classes of question which have recently been of much interest to the condensed matter community: non-equilibrium steady states, and quantum systems undergoing a global quench. Our discussion focuses on the main physical insights obtained from the gravity approaches, rather than comprehensive treatment of each topic or detailed descriptions of gravity calculations. The paper also includes an overview of current numerical techniques, as ...

  • New materials physics
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-11-27
    Paul C Canfield

    This review presents a survey of, and guide to, new materials physics (NMP) research. It begins with an overview of the goals of NMP and then presents important ideas and techniques for the design and growth of new materials. An emphasis is placed on the use of compositional phase diagrams to inform and motivate solution growth of single crystals. The second half of this review focuses on the vital process of generating actionable ideas for the growth and discovery of new materials and ground states. Motivations ranging from (1) wanting a specific compound, to (2) wanting a specific ground state to (3) wanting to explore for known and unknown unknowns, will be discussed and illustrated with abundant examples. The goal of this review is to inform, inspire, an even entertain, as many practitioners of this field as possible.

  • Quantum imaging and information
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-11-19
    Omar S Magaña-Loaiza and Robert W Boyd

    The maturity of fields such as optical physics and quantum optics has brought with it a new era where the photon represents a promising information resource. In the past few years, scientists and engineers have exploited multiple degrees of freedom of the photon to perform information processing for a wide variety of applications. Of particular importance, the transverse spatial degree of freedom has offered a flexible platform to test complex quantum information protocols in a relatively simple fashion. In this regard, novel imaging techniques that exploit the quantum properties of light have also been investigated. In this review article, we define the fundamental parameters that describe the spatial wavefunction of the photon and establish their importance for applications in quantum information processing. More specifically, we describe the underlying physics behind remarkable protocols in which information is processed through high-dimensional spatial states of photons with...

  • Multifractal analysis of financial markets: a review
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-11-19
    Zhi-Qiang Jiang, Wen-Jie Xie, Wei-Xing Zhou and Didier Sornette

    Multifractality is ubiquitously observed in complex natural and socioeconomic systems. Multifractal analysis provides powerful tools to understand the complex nonlinear nature of time series in diverse fields. Inspired by its striking analogy with hydrodynamic turbulence, from which the idea of multifractality originated, multifractal analysis of financial markets has bloomed, forming one of the main directions of econophysics. We review the multifractal analysis methods and multifractal models adopted in or invented for financial time series and their subtle properties, which are applicable to time series in other disciplines. We survey the cumulating evidence for the presence of multifractality in financial time series in different markets and at different time periods and discuss the sources of multifractality. The usefulness of multifractal analysis in quantifying market inefficiency, in supporting risk management and in developing other applications is presented. We finally...

  • Fluorite-structure antiferroelectrics
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-11-07
    Min Hyuk Park and Cheol Seong Hwang

    Ferroelectricity in fluorite-structure oxides like hafnia and zirconia have attracted increasing interest since 2011. Two spontaneous polarizations of the fluorite-structure ferroelectrics are considered highly promising for nonvolatile memory applications, with their superior scalability and Si compatibility compared to the conventional perovskite-structure ferroelectrics. Besides, antiferroelectricity originating from a field-induced phase transition between the paraelectric and ferroelectric phases in fluorite-structure oxides is another highly interesting matter. It was suggested that the field-induced phase transition could be utilized for energy conversions between thermal and electrical energy, as well as for energy storage. The important energy-related applications of antiferroelectric fluorite-structure oxides, however, have not been systematically reviewed to date. Thus, in this work, the fluorite-structure antiferroelectrics are reviewed from their fundamentals to the...

  • Strong gravitational lensing of explosive transients
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-11-07
    Masamune Oguri

    Recent rapid progress in time domain surveys makes it possible to detect various types of explosive transients in the Universe in large numbers, some of which will be gravitationally lensed into multiple images. Although a large number of strongly lensed distant galaxies and quasars have already been discovered, strong lensing of explosive transients opens up new applications, including improved measurements of cosmological parameters, powerful probes of small scale structure of the Universe, and new observational tests of dark matter scenarios, thanks to their rapidly evolving light curves as well as their compact sizes. In particular, compact sizes of emitting regions of these transient events indicate that wave optics effects play an important role in some cases, which can lead to totally new applications of these lensing events. Recently we have witnessed first discoveries of strongly lensed supernovae, and strong lensing events of other types of explosive transients such as...

  • Real-time studies of ferroelectric domain switching: a review
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-11-07
    Linze Li, Lin Xie and Xiaoqing Pan

    Ferroelectric materials have been utilized in a broad range of electronic, optical, and electromechanical applications and hold the promise for the design of future high-density nonvolatile memories and multifunctional nano-devices. The applications of ferroelectric materials stem from the ability to switch polarized domains by applying an electric field, and therefore a fundamental understanding of the switching dynamics is critical for design of practical devices. In this review, we summarize the progress in the study of the microscopic process of ferroelectric domain switching using recently developed in situ transmission electron microscopy (TEM). We first briefly introduce the instrumentation, experimental procedures, imaging mechanisms, and analytical methods of the state-of-the-art in situ TEM techniques. The application of these techniques to studying a wide range of complex switching phenomena, including domain nucleation, domain wall motion, domain relaxa...

  • Geometric phases in 2D and 3D polarized fields: geometrical, dynamical, and topological aspects
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-10-30
    Konstantin Y Bliokh, Miguel A Alonso and Mark R Dennis

    Geometric phases are a universal concept that underpins numerous phenomena involving multi-component wave fields. These polarization-dependent phases are inherent in interference effects, spin–orbit interaction phenomena, and topological properties of vector wave fields. Geometric phases have been thoroughly studied in two-component fields, such as two-level quantum systems or paraxial optical waves. However, their description for fields with three or more components, such as generic nonparaxial optical fields routinely used in modern nano-optics, constitutes a nontrivial problem. Here we describe geometric, dynamical, and total phases calculated along a closed spatial contour in a multi-component complex field, with particular emphasis on 2D (paraxial) and 3D (nonparaxial) optical fields. We present several equivalent approaches: (i) an algebraic formalism, universal for any multi-component field; (ii) a dynamical approach using the Coriolis coupling between the spin angular mo...

  • Towards understanding two-level-systems in amorphous solids: insights from quantum circuits
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-10-30
    Clemens Müller, Jared H Cole and Jürgen Lisenfeld

    Amorphous solids show surprisingly universal behaviour at low temperatures. The prevailing wisdom is that this can be explained by the existence of two-state defects within the material. The so-called standard tunneling model has become the established framework to explain these results, yet it still leaves the central question essentially unanswered—what are these two-level defects (TLS)? This question has recently taken on a new urgency with the rise of superconducting circuits in quantum computing, circuit quantum electrodynamics, magnetometry, electrometry and metrology. Superconducting circuits made from aluminium or niobium are fundamentally limited by losses due to TLS within the amorphous oxide layers encasing them. On the other hand, these circuits also provide a novel and effective method for studying the very defects which limit their operation. We can now go beyond ensemble measurements and probe individual defects—observing the quantum nature of their dynamic...

  • Anomalies in the pseudogap phase of the cuprates: competing ground states and the role of umklapp scattering
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-10-30
    Neil J Robinson, Peter D Johnson, T Maurice Rice and Alexei M Tsvelik

    Over the past two decades, advances in computational algorithms have revealed a curious property of the two-dimensional Hubbard model (and related theories) with hole doping: the presence of close-in-energy competing ground states that display very different physical properties. On the one hand, there is a complicated state exhibiting intertwined spin, charge, and pair density wave orders. We call this ‘type A’ . On the other hand, there is a uniform d -wave superconducting state that we denote as ‘type B’ . We advocate, with the support of both microscopic theoretical calculations and experimental data, dividing the high-temperature cuprate superconductors into two corresponding families, whose properties reflect either the type A or type B ground states at low temperatures. We review the anomalous properties of the pseudogap phase that led us to this picture, and present a modern perspective on the role that umklapp scattering plays in these phenomena in the ...

  • An introductory review of the resource theory approach to thermodynamics
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-10-22
    Matteo Lostaglio

    I give a self-contained introduction to the resource theory approach to quantum thermodynamics. I will introduce in an elementary manner the technical machinery necessary to unpack and prove the core statements of the theory. The topics covered include the so-called ‘many second laws of thermodynamics’, thermo-majorisation and symmetry constraints on the evolution of quantum coherence. Among the elementary applications, I explicitly work out the bounds on deterministic work extraction and formation, discuss the complete solution of the theory for a single qubit and present the irreversibility of coherence transfers. The aim is to facilitate the task of those researchers interested in engaging and contributing to this topic, presenting scope and motivation of its core assumptions and discussing the relation between the resource theory and complementary approaches.

  • Symphony on strong field approximation
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-10-13
    Kasra Amini, Jens Biegert, Francesca Calegari, Alexis Chacón, Marcelo F Ciappina, Alexandre Dauphin, Dmitry K Efimov, Carla Figueira de Morisson Faria, Krzysztof Giergiel, Piotr Gniewek, Alexandra S Landsman, Michał Lesiuk, Michał Mandrysz, Andrew S Maxwell, Robert Moszyński, Lisa Ortmann, Jose Antonio Pérez-Hernández, Antonio Picón, Emilio Pisanty, Jakub Prauzner-Bechcicki, Krzysztof Sacha, Noslen Suárez, Amelle Zaïr, Jakub Zakrzewski and Maciej Lewenstein

    This paper has been prepared by the Symphony collaboration (University of Warsaw, Uniwersytet Jagielloński, DESY/CNR and ICFO) on the occasion of the 25th anniversary of the ‘simple man’s models’ which underlie most of the phenomena that occur when intense ultrashort laser pulses interact with matter. The phenomena in question include high-harmonic generation (HHG), above-threshold ionization (ATI), and non-sequential multielectron ionization (NSMI). ‘Simple man’s models’ provide both an intuitive basis for understanding the numerical solutions of the time-dependent Schrödinger equation and the motivation for the powerful analytic approximations generally known as the strong field approximation (SFA). In this paper we first review the SFA in the form developed by us in the last 25 years. In this approach the SFA is a method to solve the TDSE, in which the non-perturbative interactions are described by including continuum–continuum interactions in a systematic perturbation-like t...

  • Programmable interactions with biomimetic DNA linkers at fluid membranes and interfaces
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-10-01
    Bortolo Matteo Mognetti, Pietro Cicuta and Lorenzo Di Michele

    At the heart of the structured architecture and complex dynamics of biological systems are specific and timely interactions operated by biomolecules. In many instances, biomolecular agents are spatially confined to flexible lipid membranes where, among other functions, they control cell adhesion, motility and tissue formation. Besides being central to several biological processes, multivalent interactions mediated by reactive linkers confined to deformable substrates underpin the design of synthetic-biological platforms and advanced biomimetic materials. Here we review recent advances on the experimental study and theoretical modelling of a heterogeneous class of biomimetic systems in which synthetic linkers mediate multivalent interactions between fluid and deformable colloidal units, including lipid vesicles and emulsion droplets. Linkers are often prepared from synthetic DNA nanostructures, enabling full programmability of the thermodynamic and kinetic properties of th...

  • Long-lived particles at the energy frontier: the MATHUSLA physics case
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-10-01
    David Curtin, Marco Drewes, Matthew McCullough, Patrick Meade, Rabindra N Mohapatra, Jessie Shelton, Brian Shuve, Elena Accomando, Cristiano Alpigiani, Stefan Antusch, Juan Carlos Arteaga-Velázquez, Brian Batell, Martin Bauer, Nikita Blinov, Karen Salomé Caballero-Mora, Jae Hyeok Chang, Eung Jin Chun, Raymond T Co, Timothy Cohen, Peter Cox, Nathaniel Craig, Csaba Csáki, Yanou Cui, Francesco D’Eramo, Luigi Delle Rose, P S Bhupal Dev, Keith R Dienes, Jeff A Dror, Rouven Essig, Jared A Evans, Jason L Evans, Arturo Fernández Tellez, Oliver Fischer, Thomas Flacke, Anthony Fradette, Claudia Frugiuele, Elina Fuchs, Tony Gherghetta, Gian F Giudice, Dmitry Gorbunov, Rick S Gupta, Claudia Hagedorn, Lawrence J Hall, Philip Harris, Juan Carlos Helo, Martin Hirsch, Yonit Hochberg, Anson Hook, Alejandro Ibarra, Seyda Ipek, Sunghoon Jung, Simon Knapen, Eric Kuflik, Zhen Liu, Salvator Lombardo, H J Lubatti, David McKeen, Emiliano Molinaro, Stefano Moretti, Natsumi Nagata, Matthias Neubert, J..

    We examine the theoretical motivations for long-lived particle (LLP) signals at the LHC in a comprehensive survey of standard model (SM) extensions. LLPs are a common prediction of a wide range of theories that address unsolved fundamental mysteries such as naturalness, dark matter, baryogenesis and neutrino masses, and represent a natural and generic possibility for physics beyond the SM (BSM). In most cases the LLP lifetime can be treated as a free parameter from the ##IMG## [http://ej.iop.org/images/0034-4885/82/11/116201/ropab28d6ieqn001.gif] m scale up to the Big Bang Nucleosynthesis limit of ##IMG## [http://ej.iop.org/images/0034-4885/82/11/116201/ropab28d6ieqn002.gif] m. Neutral LLPs with lifetimes above ##IMG## [http://ej.iop.org/images/0034-4885/82/11/116201/ropab28d6ieqn003.gif] 100 m are particularly difficult to probe, as the sensitivity of the LHC main detectors is limited by challenging backgr...

  • A review of giant correlation-length effects via proximity and weak-links coupling in a critical system: 4 He near the superfluid transition
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-10-01
    J K Perron, M O Kimball and F M Gasparini

    We review measurements of 4 He near the superfluid transition in arrangements whereby an array of weak links couple relatively larger, more bulk-like 4 He regions. In contrast to experiments which focus on the dependence of the superflow on the chemical potential difference across the links, these studies focus on the specific heat of both the weak links and that of the larger coupled regions, as well as the behavior of the superfluid fraction within the weak links. The data show unexpected results which reflect a very long range coupling as well as modification of the weak link itself due to the proximity to bulk-like helium. One finds that while the three-dimensional correlation length ##IMG## [http://ej.iop.org/images/0034-4885/82/11/114501/ropab3df5ieqn001.gif] , where ##IMG## [http://ej.iop.org/images/0034-4885/82/11/114501/ropab3df5ieqn002.gif] , is involved in these long-range effects, the distance over w...

  • Optical antennas driven by quantum tunneling: a key issues review
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-10-01
    Markus Parzefall and Lukas Novotny

    Analogous to radio- and microwave antennas, optical nanoantennas are devices that receive and emit radiation at optical frequencies. Until recently, the realization of electrically driven optical antennas was an outstanding challenge in nanophotonics. In this review we discuss and analyze recent reports in which quantum tunneling—specifically inelastic electron tunneling—is harnessed as a means to convert electrical energy into photons, mediated by optical antennas. To aid this analysis we introduce the fundamentals of optical antennas and inelastic electron tunneling. Our discussion is focused on recent progress in the field and on future directions and opportunities.

  • Observational diversity of magnetized neutron stars
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-09-23
    Teruaki Enoto, Shota Kisaka and Shinpei Shibata

    Young and rotation-powered neutron stars (NSs) are commonly observed as rapidly-spinning pulsars. They dissipate their rotational energy by emitting pulsar wind with electromagnetic radiation and spin down at a steady rate, according to the simple steadily-rotating magnetic dipole model. In reality, however, multiwavelength observations of radiation from the NS surface and magnetosphere have revealed that the evolution and properties of NSs are highly diverse, often dubbed as ‘NS zoo’. In particular, many of young and highly magnetized NSs show a high degree of activities, such as sporadic electromagnetic outbursts and irregular changes in pulse arrival times. Importantly, their magnetic field, which are the strongest in the universe, makes them ideal laboratories for fundamental physics. A class of highly-magnetized isolated NSs is empirically divided into several subclasses. In a broad classification, they are, in the order of the magnetic field strength ( B ) from the hi...

  • One-dimensional mixtures of several ultracold atoms: a review
    Rep. Prog. Phys. (IF 16.620) Pub Date : 
    Tomasz Sowiński and Miguel Ángel García-March

    Recent theoretical and experimental progress on studying one-dimensional systems of bosonic, fermionic, and Bose–Fermi mixtures of a few ultracold atoms confined in traps is reviewed in the broad context of mesoscopic quantum physics. We pay special attention to limiting cases of very strong or very weak interactions and transitions between them. For bosonic mixtures, we describe the developments in systems of three and four atoms as well as different extensions to larger numbers of particles. We also briefly review progress in the case of spinor Bose gases of a few atoms. For fermionic mixtures, we discuss a special role of spin and present a detailed discussion of the two- and three-atom cases. We discuss the advantages and disadvantages of different computation methods applied to systems with intermediate interactions. In the case of very strong repulsion, close to the infinite limit, we discuss approaches based on effective spin chain descriptions. We also report on recent s...

  • Green’s functions for geophysics: a review
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-09-03
    Ernian Pan

    The Green’s function (GF) method, which makes use of GFs, is an important and elegant tool for solving a given boundary-value problem for the differential equation from a real engineering or physical field. Under a concentrated source, the solution of a differential equation is called a GF, which is singular at the source location, yet is very fundamental and powerful. When looking at the GFs from different physical and/or engineering fields, i.e. assigning the involved functions to real physical/engineering quantities, the GFs can be scaled and applied to large-scale problems such as those involved in Earth sciences as well as to nano-scale problems associated with quantum nanostructures. GFs are ubiquitous and everywhere: they can describe heat, water pressure, fluid flow potential, electromagnetic (EM) and gravitational potentials, and the surface tension of soap film. In the undergraduate courses Mechanics of Solids and Structural Analysis, a GF is the simple influence line ...

  • Tin titanate—the hunt for a new ferroelectric perovskite
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-08-27
    J Gardner, Atul Thakre, Ashok Kumar and J F Scott

    We review all the published literature and show that there is no experimental evidence for homogeneous tin titanate SnTiO 3 in bulk or thin-film form. Instead a combination of unrelated artefacts are easily misinterpreted. The x-ray Bragg data are contaminated by double scattering from the Si substrate, giving a strong line at the 2 θ angle exactly where perovskite SnTiO 3 should appear. The strong dielectric divergence near 560 K is irreversible and arises from oxygen site detrapping, accompanied by Warburg/Randles interfacial anomalies. The small (4 µ C cm −2 ) apparent ferroelectric hysteresis remains in samples shown to be pure (Sn,Ti)O 2 rutile/cassiterite, in which ferroelectricity is forbidden. Only very recent work reveals real bulk SnTiO 3 , but it possesses an ilmenite-like structure with an elaborate array of stacking faults, not suitable for ferroelectric devices. Unpublished TEM data reveal an inhomogeneous...

  • Fundamental mechanisms for molecular energy conversion and chemical reactions at surfaces
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-08-20
    G Barratt Park, Bastian C Krüger, Dmitriy Borodin, Theofanis N Kitsopoulos and Alec M Wodtke

    The dream of theoretical surface chemistry is to predict the outcome of reactions in order to find the ideal catalyst for a certain application. Having a working ab initio theory in hand would not only enable these predictions but also provide insights into the mechanisms of surface reactions. The development of theoretical models can be assisted by experimental studies providing benchmark data. Though for some reactions a quantitative agreement between experimental observations and theoretical calculations has been achieved, theoretical surface chemistry is in general still far away from gaining predictive power. Here we review recent experimental developments towards the understanding of surface reactions. It is demonstrated how quantum-state resolved scattering experiments on reactive and nonreactive systems can be used to test front-running theoretical approaches. Two challenges for describing dynamics at surfaces are addressed: nonadiabaticity in diatomic molecule su...

  • Horndeski theory and beyond: a review
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-07-08
    Tsutomu Kobayashi

    This article is intended to review the recent developments in the Horndeski theory and its generalization, which provide us with a systematic understanding of scalar–tensor theories of gravity as well as a powerful tool to explore astrophysics and cosmology beyond general relativity. This review covers the generalized Galileons, (the rediscovery of) the Horndeski theory, cosmological perturbations in the Horndeski theory, cosmology with a violation of the null energy condition, degenerate higher-order scalar–tensor theories and their status after GW170817, the Vainshtein screening mechanism in the Horndeski theory and beyond, and hairy black hole solutions.

  • Interacting Majorana fermions
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-07-01
    Armin Rahmani and Marcel Franz

    Majorana fermions are the real (in a mathematical sense) counterparts of complex fermions like ordinary electrons. The promise of topological quantum computing has lead to substantial experimental progress in realizing these particles in various synthetic platforms. The realization of Majorana fermions motivates a fundamental question: what phases of matter can emerge if many Majorana fermions are allowed to interact? Here we review recent progress in this direction on the proposed experimental setups, analytical and numerical results on low-dimensional lattice models, and the exactly solvable Sachdev–Ye–Kitaev model. The early progress thus far suggests that strongly correlated phases of matter with Majorana building blocks can exhibit many novel phenomena, such as emergent spacetime supersymmetry, topological order and the physics of black-holes, in condensed matter systems. They may also provide alternative avenues for universal topological quantum computing through the reali...

  • Review of cosmic phase transitions: their significance and experimental signatures
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-06-24
    Anupam Mazumdar and Graham White

    The study of cosmic phase transitions are of central interest in modern cosmology. In the standard model of cosmology the Universe begins in a very hot state, right after at the end of inflation via the process of reheating/preheating, and cools to its present temperature as the Universe expands. Both new and existing physics at any scale can be responsible for catalyzing either first, second or cross over phase transition, which could be either thermal or non-thermal with a potential observable imprints. Thus this field prompts a rich dialogue between gravity, particle physics and cosmology. It is all but certain that at least two cosmic phase transitions have occurred—the electroweak and the QCD phase transitions. The focus of this review will be primarily on phase transitions above such scales, We review different types of phase transitions that can appear in our cosmic history, and their applications and experimental signatures in particular in the context of exciting gravit...

  • Quantum fidelity measures for mixed states
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-06-23
    Yeong-Cherng Liang, Yu-Hao Yeh, Paulo E M F Mendonça, Run Yan Teh, Margaret D Reid and Peter D Drummond

    Applications of quantum technology often require fidelities to quantify performance. These provide a fundamental yardstick for the comparison of two quantum states. While this is straightforward in the case of pure states, it is much more subtle for the more general case of mixed quantum states often found in practice. A large number of different proposals exist. In this review, we summarize the required properties of a quantum fidelity measure, and compare them, to determine which properties each of the different measures has. We show that there are large classes of measures that satisfy all the required properties of a fidelity measure, just as there are many norms of Hilbert space operators, and many measures of entropy. We compare these fidelities, with detailed proofs of their properties. We also summarize briefly the applications of these measures in teleportation, quantum memories and quantum computers, quantum communications, and quantum phase-space simulations.

  • The spin structure of the nucleon
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-06-10
    Alexandre Deur, Stanley J Brodsky and Guy F de Téramond

    We review the present understanding of the spin structure of protons and neutrons, the fundamental building blocks of nuclei collectively known as nucleons. The field of nucleon spin provides a critical window for testing Quantum Chromodynamics (QCD), the gauge theory of the strong interactions, since it involves fundamental aspects of hadron structure which can be probed in detail in experiments, particularly deep inelastic lepton scattering on polarized targets. QCD was initially probed in high energy deep inelastic lepton scattering with unpolarized beams and targets. With time, interest shifted from testing perturbative QCD to illuminating the nucleon structure itself. In fact, the spin degrees of freedom of hadrons provide an essential and detailed verification of both perturbative and nonperturbative QCD dynamics. Nucleon spin was initially thought of coming mostly from the spin of its quark constituents, based on intuition from the parton model. However, the...

  • Memory effects in the long-wave infrared avalanche ionization of gases: a review of recent progress
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-05-20
    E M Wright, S W Koch, M Kolesik and J V Moloney

    There are currently intense efforts being directed towards extending the range and energy of long distance nonlinear pulse propagation in the atmosphere by moving to longer infrared wavelengths, with the purpose of mitigating the effects of turbulence. In addition, picosecond and longer pulse durations are being used to increase the pulse energy. While both of these tacks promise improvements in applications, such as remote sensing and directed energy, they open up fundamental issues regarding the standard model used to calculate the nonlinear optical properties of dilute gases. Amongst these issues is that for longer wavelengths and longer pulse durations, exponential growth of the laser-generated electron density, the so-called avalanche ionization, can limit the propagation range via nonlinear absorption and plasma defocusing. It is therefore important for the continued development of the field to assess the theory and role of avalanche ionization in gases for longer waveleng...

  • The matrix environmental and cell mechanical properties regulate cell migration and contribute to the invasive phenotype of cancer cells
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2019-05-20
    Claudia Tanja Mierke

    The minimal structural unit of a solid tumor is a single cell or a cellular compartment such as the nucleus. A closer look inside the cells reveals that there are functional compartments or even structural domains determining the overall properties of a cell such as the mechanical phenotype. The mechanical interaction of these living cells leads to the complex organization such as compartments, tissues and organs of organisms including mammals. In contrast to passive non-living materials, living cells actively respond to the mechanical perturbations occurring in their microenvironment during diseases such as fibrosis and cancer. The transformation of single cancer cells in highly aggressive and hence malignant cancer cells during malignant cancer progression encompasses the basement membrane crossing, the invasion of connective tissue, the stroma microenvironments and transbarrier migration, which all require the immediate interaction of the aggressive and invasive cancer cells ...

  • Electronic and optical properties of strained graphene and other strained 2D materials: a review
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2017-08-21
    Gerardo G Naumis, Salvador Barraza-Lopez, Maurice Oliva-Leyva, Humberto Terrones

    This review presents the state of the art in strain and ripple-induced effects on the electronic and optical properties of graphene. It starts by providing the crystallographic description of mechanical deformations, as well as the diffraction pattern for different kinds of representative deformation fields. Then, the focus turns to the unique elastic properties of graphene, and to how strain is produced. Thereafter, various theoretical approaches used to study the electronic properties of strained graphene are examined, discussing the advantages of each. These approaches provide a platform to describe exotic properties, such as a fractal spectrum related with quasicrystals, a mixed Dirac–Schrödinger behavior, emergent gravity, topological insulator states, in molecular graphene and other 2D discrete lattices. The physical consequences of strain on the optical properties are reviewed next, with a focus on the Raman spectrum. At the same time, recent advances to tune the optical conductivity of graphene by strain engineering are given, which open new paths in device applications. Finally, a brief review of strain effects in multilayered graphene and other promising 2D materials like silicene and materials based on other group-IV elements, phosphorene, dichalcogenide- and monochalcogenide-monolayers is presented, with a brief discussion of interplays among strain, thermal effects, and illumination in the latter material family.

  • Light weakly interacting massive particles
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2017-06-14
    Graciela B Gelmini

    Light weakly interacting massive particles (WIMPs) are dark matter particle candidates with weak scale interaction with the known particles, and mass in the GeV to tens of GeV range. Hints of light WIMPs have appeared in several dark matter searches in the last decade. The unprecedented possible coincidence into tantalizingly close regions of mass and cross section of four separate direct detection experimental hints and a potential indirect detection signal in gamma rays from the galactic center, aroused considerable interest in our field. Even if these hints did not so far result in a discovery, they have had a significant impact in our field. Here we review the evidence for and against light WIMPs as dark matter candidates and discuss future relevant experiments and observations.

  • Impact of new data for neutron-rich heavy nuclei on theoretical models for r-process nucleosynthesis
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2017-05-23
    Toshitaka Kajino, Grant J Mathews

    Current models for therprocess are summarized with an emphasis on the key constraints from both nuclear physics measurements and astronomical observations. In particular, we analyze the importance of nuclear physics input such as beta-decay rates; nuclear masses; neutron-capture cross sections; beta-delayed neutron emission; probability of spontaneous fission, beta- and neutron-induced fission, fission fragment mass distributions; neutrino-induced reaction cross sections, etc. We highlight the effects on models forr-process nucleosynthesis of newly measuredβ-decay half-lives, masses, and spectroscopy of neutron-rich nuclei near ther-process path. We overviewr-process nucleosynthesis in the neutrino driven wind above the proto-neutron star in core collapse supernovae along with the possibility of magneto-hydrodynamic jets from rotating supernova explosion models. We also consider the possibility of neutron star mergers as anr-process environment. A key outcome of newly measured nuclear properties far from stability is the degree of shell quenching for neutron rich isotopes near the closed neutron shells. This leads to important constraints on the sites forr-process nucleosynthesis in which freezeout occurs on a rapid timescale.

  • Characteristics and controllability of vortices in ferromagnetics, ferroelectrics, and multiferroics
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2017-06-02
    Yue Zheng, W J Chen

    Topological defects in condensed matter are attracting e significant attention due to their important role in phase transition and their fascinating characteristics. Among the various types of matter, ferroics which possess a switchable physical characteristic and form domain structure are ideal systems to form topological defects. In particular, a special class of topological defects—vortices—have been found to commonly exist in ferroics. They often manifest themselves as singular regions where domains merge in large systems, or stabilize as novel order states instead of forming domain structures in small enough systems. Understanding the characteristics and controllability of vortices in ferroics can provide us with deeper insight into the phase transition of condensed matter and also exciting opportunities in designing novel functional devices such as nano-memories, sensors, and transducers based on topological defects. In this review, we summarize the recent experimental and theoretical progress in ferroic vortices, with emphasis on those spin/dipole vortices formed in nanoscale ferromagnetics and ferroelectrics, and those structural domain vortices formed in multiferroic hexagonal manganites. We begin with an overview of this field. The fundamental concepts of ferroic vortices, followed by the theoretical simulation and experimental methods to explore ferroic vortices, are then introduced. The various characteristics of vortices (e.g. formation mechanisms, static/dynamic features, and electronic properties) and their controllability (e.g. by size, geometry, external thermal, electrical, magnetic, or mechanical fields) in ferromagnetics, ferroelectrics, and multiferroics are discussed in detail in individual sections. Finally, we conclude this review with an outlook on this rapidly developing field.

  • Anisotropy in Quasi-Static Magnetohydrodynamic Turbulence
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2017-05-11
    Mahendra K Verma

    In this review we summarise the current status of the quasi-static magnetohydrodynamic turbulence. The energy spectrum is steeper than Kolmogorov'sk−5/3spectrum due to the decrease of the kinetic energy flux with wavenumberkas a result of Joule dissipation. The spectral index decreases with the increase of interaction parameter. The flow is quasi two-dimensional with strongat smallkand weakat largek, whereandare the perpendicular and parallel components of velocity relative to the external magnetic field. For smallk, the energy flux ofis negative, but for largek, the energy flux ofis positive. Pressure mediates the energy transfer fromto.

  • The black hole information problem: past, present, and future
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2017-07-21
    Donald Marolf

    We give a brief overview of the black hole information problem emphasizing fundamental issues and recent proposals for its resolution. The focus is on broad perspective and providing a guide to current literature rather than presenting full details. We concentrate on resolutions restoring naive unitarity.

  • Information loss
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2017-07-21
    William G Unruh, Robert M Wald

    The complete gravitational collapse of a body in general relativity will result in the formation of a black hole. Although the black hole is classically stable, quantum particle creation processes will result in the emission of Hawking radiation to infinity and corresponding mass loss of the black hole, eventually resulting in the complete evaporation of the black hole. Semiclassical arguments strongly suggest that, in the process of black hole formation and evaporation, a pure quantum state will evolve to a mixed state, i.e. there will be 'information loss'. There has been considerable controversy over this issue for more than 40 years. In this review, we present the arguments in favor of information loss, and analyze some of the counter-arguments and alternative possibilities.

  • Origins of life: a problem for physics, a key issues review
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2017-08-14
    Sara Imari Walker

    The origins of life stands among the great open scientific questions of our time. While a number of proposals exist for possible starting points in the pathway from non-living to living matter, these have so far not achieved states of complexity that are anywhere near that of even the simplest living systems. A key challenge is identifying the properties of living matter that might distinguish living and non-living physical systems such that we might build new life in the lab. This review is geared towards covering major viewpoints on the origin of life for those new to the origin of life field, with a forward look towards considering what it might take for a physical theory thatuniversallyexplains the phenomenon of life to arise from the seemingly disconnected array of ideas proposed thus far. The hope is that a theory akin to our other theories in fundamental physics might one day emerge to explain the phenomenon of life, and in turn finally permit solving its origins.

  • Reconfigurable metamaterials for terahertz wave manipulation
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2017-07-17
    Mohammed R Hashemi, Semih Cakmakyapan, Mona Jarrahi

    Reconfigurable metamaterials have emerged as promising platforms for manipulating the spectral and spatial properties of terahertz waves without being limited by the characteristics of naturally existing materials. Here, we present a comprehensive overview of various types of reconfigurable metamaterials that are utilized to manipulate the intensity, phase, polarization, and propagation direction of terahertz waves. We discuss various reconfiguration mechanisms based on optical, electrical, thermal, and mechanical stimuli while using semiconductors, superconductors, phase-change materials, graphene, and electromechanical structures. The advantages and disadvantages of different reconfigurable metamaterial designs in terms of modulation efficiency, modulation bandwidth, modulation speed, and system complexity are discussed in detail.

  • Binary neutron star mergers: a review of Einstein’s richest laboratory
    Rep. Prog. Phys. (IF 16.620) Pub Date : 2017-07-07
    Luca Baiotti, Luciano Rezzolla

    In a single process, the merger of binary neutron star systems combines extreme gravity, the copious emission of gravitational waves, complex microphysics and electromagnetic processes, which can lead to astrophysical signatures observable at the largest redshifts. We review here the recent progress in understanding what could be considered Einstein's richest laboratory, highlighting in particular the numerous significant advances of the last decade. Although special attention is paid to the status of models, techniques and results for fully general-relativistic dynamical simulations, a review is also offered on the initial data and advanced simulations with approximate treatments of gravity. Finally, we review the considerable amount of work carried out on the post-merger phase, including black-hole formation, torus accretion onto the merged compact object, the connection with gamma-ray burst engines, ejected material, and its nucleosynthesis.

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