Abstract
Geometric phases in condensed matter play a central role in topological transport phenomena such as the quantum, spin and anomalous Hall effect (AHE). In contrast to the quantum Hall effect - which is characterized by a topological invariant and robust against perturbations - the AHE depends on the Berry curvature of occupied bands at the Fermi level and is therefore highly sensitive to subtle changes in the band structure. A unique platform for its manipulation is provided by transition metal oxide heterostructures, where engineering of emergent electrodynamics becomes possible at atomically sharp interfaces. We demonstrate that the Berry curvature and its corresponding vector potential can be manipulated by interface engineering of the correlated itinerant ferromagnet SrRuO$_3$ (SRO). Measurements of the AHE reveal the presence of two interface-tunable spin-polarized conduction channels. Using theoretical calculations, we show that the tunability of the AHE at SRO interfaces arises from the competition between two topologically non-trivial bands. Our results demonstrate how reconstructions at oxide interfaces can be used to control emergent electrodynamics on a nanometer-scale, opening new routes towards spintronics and topological electronics.
Highlights
In topologically nontrivial band structures, electrons acquire an additional phase factor when their wave functions traverse a closed loop in momentum space [1]
We discuss the scenario proposed here in the context of recent studies performed on SRO thin films and heterostructures, where similar anomalous Hall characteristics were observed and attributed to the topological Hall effect due to a skyrmion phase [19,29,60]
Within this picture the topological Hall effect would be enhanced in the SIO/SRO/SIO case due to Dzyaloshinskii-Moriya interaction at both interfaces, our data cannot exclude contributions from real-space Berry curvature effects due to noncollinear spin textures forming in a specific range of temperature and magnetic fields
Summary
In topologically nontrivial band structures, electrons acquire an additional phase factor when their wave functions traverse a closed loop in momentum space [1]. The behavior and control of the AHE in SRO ultrathin films and heterostructures have been at the center of intense research [19,20,21,22,23,24,25,26,27,28], fueled by the observation of humplike features in the transverse resistivity [29] Such features are generally considered to be a manifestation of the topological Hall effect (THE). We reveal spin-polarized topologically nontrivial bands at the Fermi energy, associated with sources of Berry curvature, bringing about competing contributions to the anomalous Hall response. We subsequently use these insights to investigate theoretically and experimentally the AHE in ultrathin SRO films with (a)symmetric boundary conditions.
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