Understanding electronic peculiarities in tetragonal FeSe as local structural symmetry breaking

Zhi Wang, Xin-Gang Zhao, Robert Koch, Simon J. L. Billinge, and Alex Zunger
Phys. Rev. B 102, 235121 – Published 9 December 2020

Abstract

Traditional band theory of perfect crystalline solids often uses as input the structure deduced from diffraction experiments; when modeled by the minimal unit cell this often produces a spatially averaged model. The present study illustrates that this is not always a safe practice unless one examines if the intrinsic bonding mechanism is capable of benefiting from the formation of a distribution of lower symmetry local environments that differ from the macroscopically averaged structure. This can happen either due to positional or to magnetic symmetry breaking. By removing the constraint of a small crystallographic cell, the energy minimization in the density functional theory finds atomic and spin symmetry breaking, not evident in conventional diffraction experiments but being found by local probes such as atomic pair distribution function analysis. Here we report that large atomic and electronic anomalies in bulk tetragonal FeSe emerge from the existence of distributions of local positional and magnetic moment motifs. The found symmetry-broken motifs obtained by minimization of the internal energy represent what chemical bonding in the tetragonal phase prefers as intrinsic energy lowering (stabilizing) static distortions. This explains observations of band renormalization, predicts orbital order and enhanced nematicity, and provides unprecedented close agreement with spectral function measured by photoemission and local atomic environment revealed by the pair distribution function. While the symmetry-restricted strong correlation approach has been argued previously to be the exclusive theory needed for describing the main peculiarities of FeSe, we show here that the symmetry-broken mean-field approach addresses numerous aspects of the problem, provides intuitive insight into the electronic structure, and opens the door for large-scale mean-field calculations for similar d-electron quantum materials.

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  • Received 22 March 2020
  • Revised 10 October 2020
  • Accepted 2 November 2020

DOI:https://doi.org/10.1103/PhysRevB.102.235121

©2020 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Zhi Wang1, Xin-Gang Zhao1, Robert Koch2, Simon J. L. Billinge2,3, and Alex Zunger1,*

  • 1University of Colorado, Renewable & Sustainable Energy Institute, Boulder, Colorado 80309, USA
  • 2Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
  • 3Department of Applied Physics and Mathematics, Columbia University, New York, New York 10027, USA

  • *Corresponding author: alex.zunger@colorado.edu

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Vol. 102, Iss. 23 — 15 December 2020

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