Magnetism and topology in SrRuO₃- and SrVO₃-based heterostructures: from DFT via DMFT to DΓA

Oxide heterostructures based on SrRuO₃ are promising candidates for thin film ferromagnetism, but experiments showed time and again that ferromagnetism breaks down below a critical thickness. By means of density functional theory (DFT) plus dynamical mean field theory (DMFT), we show [1] that growing SrRuO3 in the (111) direction instead yields a half-metallic ferromagnetic state with an ordered magnetic moment of 2 μB/Ru and survives the ultimate dimensional confinement down to a bilayer -- even at elevated temperatures of 500 K. This ferromagnetic state has been confirmed by experiment and also hosts Haldane’s quantum anomalous Hall state, without any external magnetic field or magnetic impurities [1]. Similar physics with an even larger gap is also observed in SrRhO3 (111) but not in LaNiO3 (111) [2] bilayers.

For SrRuO₃ grown in the (001)-direction, DFT+DMFT instead only yields ferromagnetism if the Ru is doped away from 4 d-electrons. This is possible by applying a gate voltage or, as we will show, by growing SrRuO₃ on an appropriate substrate that induces a self-doping between different SrRuO₃ layers.

For SrVO₃-based heterostructures, on the other hand, the metallic bulk behavior turns insulating below a thickness of 3 SrVO₃ layers, which has been proposed to be utilized as a Mott transistor [3]. Using DFT+DMFT and beyond that the dynamical vertex approximation (DΓA) [4], we here show that this insulating state is actually antiferromagnetic at low temperatures and can be switched to a ferromagnetic metallic state through a gate voltage, actually making it a Mott magnetotransistor. Here, strong non-local correlations further induce a Lifshitz transition at low temperatures.

[1] L. Si et al., PRL 119, 026402 (2017).
[2] O. Janson and KH, PRB 98, 115118 (2018).
[3] Z. Zhong et al., PRL 114, 246401 (2015).
[4] G. Rohringer et al., RMP 90, 025003 (2018).