Many-Body Physics of Single and Double Spin-Flip Excitations in NiO

Open Access

Many-Body Physics of Single and Double Spin-Flip Excitations in NiO

Abhishek Nag, H. C. Robarts, F. Wenzel, J. Li, Hebatalla Elnaggar, Ru-Pan Wang, A. C. Walters, M. García-Fernández, F. M. F. de Groot, M. W. Haverkort, and Ke-Jin Zhou

Phys. Rev. Lett. 124, 067202 – Published 13 February 2020

Abstract

Understanding many-body physics of elementary excitations has advanced our control over material properties. Here, we study spin-flip excitations in NiO using Ni $L_{3}$ -edge resonant inelastic x-ray scattering (RIXS) and present a strikingly different resonant energy behavior between single and double spin-flip excitations. Comparing our results with single-site full-multiplet ligand field theory calculations we find that the spectral weight of the double-magnon excitations originates primarily from the double spin-flip transition of the quadrupolar RIXS process within a single magnetic site. Quadrupolar spin-flip processes are among the least studied excitations, despite being important for multiferroic or spin-nematic materials due to their difficult detection. We identify intermediate state multiplets and intra-atomic core-valence exchange interactions as the key many-body factors determining the fate of such excitations. RIXS resonant energy dependence can act as a convincing proof of existence of nondipolar higher-ranked magnetic orders in systems for which, only theoretical predictions are available.

Received 8 October 2019
Accepted 16 January 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.067202

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Magnons

Antiferromagnets Magnetic insulators

Many-body techniques Resonant inelastic x-ray scattering

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Abhishek Nag^1,*, H. C. Robarts^1,2, F. Wenzel³, J. Li ^1,4, Hebatalla Elnaggar⁵, Ru-Pan Wang⁵, A. C. Walters ¹, M. García-Fernández ¹, F. M. F. de Groot⁵, M. W. Haverkort³, and Ke-Jin Zhou ^1,†

¹Diamond Light Source, Harwell Campus, Didcot OX11 0DE, United Kingdom
²H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, United Kingdom
³Institute for theoretical physics, Heidelberg University, Philosophenweg 19, 69120 Heidelberg, Germany
⁴Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
⁵Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG, Utrecht, The Netherlands

^*abhishek.nag@diamond.ac.uk
^†kejin.zhou@diamond.ac.uk

Article Text

Click to Expand

Supplemental Material

Click to Expand

References

Click to Expand

Issue

Vol. 124, Iss. 6 — 14 February 2020

Reuse & Permissions

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
All data presented in this work have been collected in the geometry shown in panel (a) [30]. Panel (b) shows the XAS collected on NiO along with the RIXS energy-transfer map upon changing incident energy. Simulation of the same map using single-site full multiplet ligand field theory implemented in quanty is shown in panel (c) marked with the RIXS final states for NiO. The main peak (MP) and satellite peak (SP) of the XAS are shown as dotted lines on the maps. Experimental RIXS incident energy line cuts at MP and SP of XAS in panel (b) are plotted separately in (d). A Gaussian line shape of instrumental resolution (45 meV) is shaded at spin-singlet state excitation to ${}^{1}{A_{1 g}}$ state for SP.
Reuse & Permissions
Figure 2
Panels (a) and (b) show enlarged view of the low energy-transfer regions of the RIXS maps presented in Fig. 1 and 1 respectively, featuring the spin-flip excitations. Low energy-transfer RIXS line spectra at MP and SP are shown in panels (c) and (d) respectively, along with fits contributed by elastic, phonon, magnon, and double-magnon peaks.
Reuse & Permissions
Figure 3
Resonance behavior of the magnon and double-magnon excitations represented by their spectral weights extracted by fitting experimental RIXS line spectrum for each incident energy is plotted in panel (a) along with XAS. In panel (b) the spectral weights obtained from simulated RIXS spectra of single-site single and double spin-flip excitations and XAS in the same range of incident energies as in panel (a) is presented. The intensities of XAS data in both panels are scaled to compare with the spin-flip spectral weights.
Reuse & Permissions
Figure 4
Schematic representation of possible single-site spin-flip states generated in a RIXS process in $d^{8}$ systems in presence of core-hole SOC and core-valence exchange Coulomb interaction ( $G_{p d}$ ) is shown in panel (a). For brevity, spin angular momentum change is shown for quantized spin projected along an axis. Distribution of intermediate states in RIXS, represented by XAS at the Ni $L_{3}$ edge are shown for varying strengths of $G_{p d}$ in panel (b). In panels (c) and (d), distribution and spectral weights of $Δ M_{s} = 1$ and $Δ M_{s} = 2$ spin-flip excitations are shown for each XAS spectrum given in panel (a). Similarly, effect of $ζ_{3 d}^{int}$ on XAS spectra and $Δ M_{s} = 1$ and $Δ M_{s} = 2$ excitations across the Ni- $L_{3}$ edge is presented in panels (e), (f), and (g), respectively. To isolate the effects of $G_{p d}$ and $ζ_{3 d}^{int}$ on the excitations, while one is varied, the other is kept fixed at zero.
Reuse & Permissions

Physical Review Letters