Electronic structure and spin-orbit driven novel magnetism in d4.5 insulator Ba3YIr2O9

TL;DR

This study uses first-principles calculations to explore the electronic structure and magnetism of Ba3YIr2O9, revealing a transition from long-range magnetic order to a quantum spin-orbital liquid under high pressure.

Contribution

It provides a detailed analysis of the interplay between spin-orbit coupling, electronic correlations, and structural phases in a d4.5 iridate, highlighting pressure-induced magnetic state changes.

Findings

AP phase exhibits intermediate SOC regime with magnetic order.

High pressure induces a structural transition to a disordered phase.

In the HP phase, SOC dominates, leading to a quantum spin-orbital liquid.

Abstract

We have carried out a detailed first-principles study of a d$^{4.5}$ quaternary iridate Ba$_3$YIr$_2$O$_9$ both in its 6H-perovskite-type ambient pressure (AP) phase and also for the high pressure (HP) cubic phase. Our analysis reveals that the AP phase belongs to the intermediate spin-orbit coupling (SOC) regime. This is further supported by the identification of the spin moment as the primary order parameter (POP) obtained from a magnetic multipolar analysis. The large $t_{2g}$ band width renormalizes the strength of SOC and the Ir intersite exchange interaction dominates resulting in long range magnetic order in the AP phase. In addition to SOC and Hubbard $U$, strong intradimer coupling is found to be crucial for the realization of the insulating state. At high pressure (HP) the system undergoes a structural transformation to the disordered cubic phase. In sharp contrast to the AP phase, the calculated exchange interactions in the HP phase are found to be much weaker and SOC dominates leading to a quantum spin orbital liquid (SOL) state.