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Register a new userCrossover from Karplus-Luttinger to Topological Hall Effects in SrRuO3-based heterostructures
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Using SrRuO3-based thin film heterostructures, we aim to resolve the two debated interpretations that distinguish between the genuine Topological Hall Effect (THE) and the artefactual humps produced from overlapping double Karplus-Luttinger Anomalous Hall Effects (KL-AHE), without magnetic imaging. Firstly, we selected two heterostructures with similar Hall Effect but with contrasting octahedral rotations/tilts, providing a clue to determining the presence/absence of Dzyaloshinskii-Moriya Interaction. Secondly, we employ the {theta}-rotation of magnetic field from out-of-plane to in-plane as the critical judgemental tool. The first heterostructure showing field-position of Hall hump diverging with ~1/cos({theta}) is correctly reproduced using the double KL-AHEs. Yet, the second one showing constant hump field versus {theta} behaviour agrees with a micromagnetic simulation with Neel-Skyrmions and is thus convincingly assigned as THE. Lastly, for a general system evolving with increasing magnetic field from two-dimensional Skyrmion-lattice into collinear ferromagnetic in the real-space, we further discuss about the corresponding evolution of k-space band structure from gapped massive Dirac Fermion into Weyl Fermion, consistent to past literatures. Its associated transformation from Mirror Anomaly into Chiral Anomaly is detectable via electrical transport and further assisted in resolving the aforementioned debate. We hence emphasize the two schemes as useful, generic electrical measurement protocols for future search of magnetic Skyrmions.
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Electron transport coupled with magnetism has attracted attention over the years as exemplified in anomalous Hall effect due to a Berry phase in momentum space. Another type of unconventional Hall effect -- topological Hall effect, originating from the real-space Berry phase, has recently become of great importance in the context of magnetic skyrmions. We have observed topological Hall effect in bilayers consisting of ferromagnetic SrRuO$_3$ and paramagnetic SrIrO$_3$ over a wide region of both temperature and magnetic field. The topological term rapidly decreases with the thickness of SrRuO$_3$, ending up with the complete disappearance at 7 unit cells of SrRuO$_3$. Combined with model calculation, we concluded that the topological Hall effect is driven by interface Dzyaloshinskii-Moriya interaction, which is caused by both the broken inversion symmetry and the strong spin-orbit coupling of SrIrO$_3$. Such interaction is expected to realize the N{e}el-type magnetic skyrmion, of which size is estimated to be $sim$10 nm from the magnitude of topological Hall resistivity. The results established that the high-quality oxide interface enables us to tune the chirality of the system; this can be a step towards the future topological electronics.
This review provides a summary of the rich physics expressed within SrTiO$_3$-based heterostructures and nanostructures. The intended audience is researchers who are working in the field of oxides, but also those with different backgrounds (e.g., semiconductor nanostructures). After reviewing the relevant properties of SrTiO$_3$ itself, we will then discuss the basics of SrTiO$_3$-based heterostructures, how they can be grown, and how devices are typically fabricated. Next, we will cover the physics of these heterostructures, including their phase diagram and coupling between the various degrees of freedom. Finally, we will review the rich landscape of quantum transport phenomena, as well as the devices that elicit them.
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