Interplay between spin-orbit coupling and Hubbard interaction in SrIrO3 and related Pbnm perovskites

TL;DR

This paper reveals that in SrIrO3 and related Pbnm perovskites, stronger spin-orbit coupling actually increases the critical Hubbard interaction needed for a Mott transition, due to protected Dirac nodes reducing electron correlation effects.

Contribution

It challenges previous assumptions by showing that in orthorhombic perovskites, stronger SOC leads to larger Uc because of Dirac node protection, affecting the phase diagram and magnetic properties.

Findings

Stronger SOC increases the critical Uc for Mott transition.

Presence of Dirac nodes results in small Fermi pockets and low density of states.

Phase diagram includes non-magnetic semimetal, magnetic metal, and magnetic insulator.

Abstract

There has been a rapidly growing interest on the interplay between spin-orbit coupling (SOC) and Hubbard interaction U in correlated materials. A current consensus is that the stronger the SOC, the smaller is the critical interaction Uc required for a spin-orbit Mott insulator, because the atomic SOC splits a band into different total angular momentum bands narrowing the effective bandwidth. It was further claimed that at large enough SOC, the stronger the SOC, the weaker the Uc because in general the effective SOC is enhanced with increasing electron-electron interaction strength. Contrary to this expectation, we find that, in orthorhombic perovskite oxides (Pbnm), the stronger the SOC, the bigger the Uc. This is originated from a line of Dirac node in Jeff=1/2 bands near the Fermi level inherited from a combination of the lattice structure and a large SOC. Due to this protected line of nodes, there are small hole and electron pockets in SrIrO3, and such a small density of states makes Hubbard interaction less efficient in building a magnetic insulator. The full phase diagram in U vs. SOC is obtained, where non-magnetic semimetal, magnetic metal, and magnetic insulator are found. Magnetic ordering patterns beyond Uc are also presented. We further discuss implications of our finding in relation to other perovskites such as SrRhO3 and SrRuO3.