Tunable real- and momentum-space topological properties in SrRuO₃ ultrathin films

In perovskite-structured SrRuO₃ (SRO), a fine balance between the electron-electron correlation and spin-orbit coupling gives rise to a variety of exotic topological properties. Here, we will show our recent results about tunable real-and momentum-space topological properties in SRO ultrathin films. First, we report the discovery of ferroelectrically tunable skyrmions in ultrathin BaTiO₃/SRO bilayer heterostructures. The ferroelectric proximity effect at the BaTiO₃/SRO heterointerface can trigger a sizable Dzyaloshinskii-Moriya interaction, thus stabilizing a real-space topological spin texture: magnetic skyrmion. By locally manipulating the ferroelectric polarization, we can achieve local, switchable, and nonvolatile control of both skyrmion density and thermodynamic stability. Second, we will focus on the highly tunable anomalous Hall effect (AHE) in SRO single layers. We found the AHE exhibit a clear sign reversal as the SRO film thickness decreases to 4 unit-cells due to the changes in momentum-space Berry curvatures. By harnessing the step-flow growth, we can induce an artificial thickness inhomogeneity and a two-channel AHE in SRO films. We developed several experimental methods for distinguishing the skyrmion-induced topological Hall effect from the two-channel AHE.