Quantum Monte Carlo study of lattice polarons in the two-dimensional three-orbital Su\u2013Schrieffer\u2013Heeger model

Shaozhi Li,Steven Johnston

doi:10.1038/s41535-020-0243-3

Abstract

The electron–lattice interaction gives rise to a rich set of phenomena in quantum materials. Microscopically, this interaction often arises from the modulation of orbital overlaps; however, many theoretical studies neglect such couplings. Here, we present an exact diagonalization and determinant quantum Monte Carlo study of a three-orbital Su–Schrieffer–Heeger (SSH) model, on a two-dimensional Lieb lattice and in the negative charge transfer regime. At half-filling (one hole/unit cell), we observe a bipolaron insulating phase with a bond-disproportionate lattice. This phase is robust against moderate hole doping but is suppressed at large hole concentrations, leading to a metallic polaron-liquid-like state with fluctuating patches of local distortions. We also find an s-wave superconducting state at large hole doping that primarily appears on the oxygen sublattice. Our work provides a non-perturbative view of SSH-type couplings in two dimensions with implications for materials where such couplings are dominant.

Highlights

Lattice dimerization, referring to an alternation of two lattice constants, occurs in many quantum materials, including the organic charge-transfer solids[1,2,3], and perovskites systems like the rare-earth nickelates RNiO34–6, and the high-temperature superconducting bismuthates Bi1−xKxBiO3 (BKBO)[7,8]
Near half-filling, we find that the system is a bipolaronic charge-density-wave (CDW) insulator with a bonddisproportionated structure, similar to what is observed in BKBO30
We find evidence for a metallic phase where holes are strongly correlated with local structural distortions, forming a polaron-liquid-like phase

Summary

Introduction

Lattice dimerization, referring to an alternation of two lattice constants, occurs in many quantum materials, including the organic charge-transfer solids[1,2,3], and perovskites systems like the rare-earth nickelates RNiO34–6, and the high-temperature (high-Tc) superconducting bismuthates Bi1−xKxBiO3 (BKBO)[7,8]. It is necessary to study this model in higher dimensions in the context of materials like RNiO3 and BKBO. We focus on BKBO and study how the SSH-type e–ph interaction produces both insulating and superconducting states as a function of doping. BKBO is in the so-called “negative charge transfer” regime[23,24,25,26], where holes self-dope from the cation to the ligand oxygen atoms. The subsequent hybridization between the cation and the oxygen atoms leads to a sizable e–ph interaction[6,7], which may be further enhanced by correlations[27], and is believed to drive a high-temperature metal-to-insulator (MIT) transition. The insulating state has a dimerized (or “bond disproportionated”) structure with expanded and collapsed

Methods

Results

Conclusion