Quantum Anomalous Hall State in Ferromagnetic SrRuO$_3$ (111) Bilayers

TL;DR

This paper predicts that SrRuO$_3$ (111) bilayers can host a quantum anomalous Hall state due to spin-orbit coupling effects, maintaining ferromagnetism and topological properties at high temperatures.

Contribution

It demonstrates, through advanced theoretical methods, that SrRuO$_3$ bilayers are a promising platform for realizing quantum anomalous Hall states without external magnetic fields.

Findings

Ferromagnetic order persists down to bilayer thickness at 500K.

Spin-orbit coupling induces a topological gap at quarter filling.

The bilayer exhibits a Chern number of 1, indicating a quantum anomalous Hall state.

Abstract

SrRuO$_3$ heterostructures grown in the (111) direction are a rare example of thin film ferromagnets. By means of density functional theory plus dynamical mean field theory we show that the half-metallic ferromagnetic state with an ordered magnetic moment of 2$\mu_{B}$/Ru survives the ultimate dimensional confinement down to a bilayer, even at elevated temperatures of 500$\,$K. In the minority channel, the spin-orbit coupling opens a gap at the linear band crossing corresponding to $\frac34$ filling of the $t_{2g}$ shell. We demonstrate that the respective state is Haldane's quantum anomalous Hall state with Chern number $C$=1, without an external magnetic field or magnetic impurities.