Theory of Large Intrinsic Spin Hall Effect in Iridate Semimetals

TL;DR

This paper theoretically demonstrates that iridate semimetals, especially SrIrO$_3$, can exhibit a large intrinsic spin Hall effect due to their electronic structure and symmetry, with potential for enhanced effects in thin films.

Contribution

It reveals the mechanism behind large intrinsic spin Hall effects in 5d transition metal oxides, highlighting the role of nodal line electronic structures and geometric confinement.

Findings

Large spin Hall conductivity comparable to topological insulators.

Robustness of the effect even when nodal lines are gapped.

Enhanced spin Hall effect in thin film geometries.

Abstract

We theoretically investigate the mechanism to generate large intrinsic spin Hall effect in iridates or more broadly in 5d transition metal oxides with strong spin-orbit coupling. We demonstrate such a possibility by taking the example of orthorhombic perovskite iridate with nonsymmorphic lattice symmetry, SrIrO$_3$, which is a three-dimensional semimetal with nodal line spectrum. It is shown that large intrinsic spin Hall effect arises in this system via the spin-Berry curvature originating from the nearly degenerate electronic spectra surrounding the nodal line. This effect exists even when the nodal line is gently gapped out, due to the persistent nearly degenerate electronic structure, suggesting a distinct robustness. The magnitude of the spin Hall conductivity is shown to be comparable to the best known example such as doped topological insulators and the biggest in any transition metal oxides. To gain further insight, we compute the intrinsic spin Hall conductivity in both of the bulk and thin film systems. We find that the geometric confinement in thin films leads to significant modifications of the electronic states, leading to even bigger spin Hall conductivity in certain cases. We compare our findings with the recent experimental report on the discovery of large spin Hall effect in SrIrO$_3$ thin films.