A Renormalization-Group Study of the Symmetry-Breaking Order Parameters in Spin-Orbit Coupled Iridates and Related Systems

TL;DR

This study uses a renormalization-group approach to analyze how spin-orbit coupling and Fermi surface nesting influence the emergence of exotic spin-orbit density waves in iridates, explaining their metal-insulator transition.

Contribution

It introduces a RG-based analysis revealing the dominance of spin-orbit density waves over conventional SDWs in spin-orbit coupled multi-orbital systems.

Findings

Spin-orbit density wave (SODW) is energetically favored in certain Fermi surface topologies.

SODW better explains experimental observations of iridates' metal-insulator transition.

Inter-band nesting enhances inter-orbital Coulomb interactions leading to SODW.

Abstract

We study the competition between various forms of density-wave-like order parameters that may arise in multi-orbital correlated materials with strong spin-orbit coupling (SOC) within a renormalization-group (RG) approach. The calculations are restricted to models with two spin-orbit split bands having strong inter-band Fermi surface nesting. We find that for such Fermi surface topology, the interplay between the inter-band nesting and SOC strongly enhances the inter-orbital Coulomb interaction (relative to other interactions) as the system approaches a stable fixed point. This results in an exotic spin-orbit density wave (SODW) to become the energetically favorable symmetry-broken state. While the conclusions are generic to such a Fermi surface topology, the band structure and the numerical results are presented for the iridate systems. We also find that the electronic fingerprints of the SODW are in better agreement with various experimental results than a conventional spin density wave (SDW), explaining the long-standing problem of the origin of the metal-insulator transition in these systems.