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1. Tunable topological Hall effects in noncollinear antiferromagnet Mn3Sn/Pt bilayers

   https://doi.org/10.1063/5.0048733  

   Cheng, Yang; Yu, Sisheng; Zhu, Menglin; Hwang, Jinwoo; Yang, Fengyuan (May 2021, APL Materials)

   Noncollinear antiferromagnet Mn3Sn has attracted wide interest as it is a candidate for Weyl semimetal. Here, we report the observation of topological Hall like signals in Mn3Sn/Pt bilayers grown on Al2O3(0001). X-ray diffraction and scanning transmission electron microscopy results confirm the high epitaxial quality of the c-axis-oriented Mn3Sn films. The detected topological Hall resistivity shows a broad temperature range from 210 to 365 K by tuning the thickness of Mn3Sn from 3 to 15 nm. Compared with previously reported topological Hall effects in Mn3Sn at temperatures below 50 K, the observed high-temperature topological Hall signal is likely due to the stabilization of topological spin textures enabled by the strong spin–orbit coupling of the Pt overlayer and the Dzyaloshinskii–Moriya interaction at the Mn3Sn/Pt interface. 

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2. Spontaneous Hall effects in the electron system at the SmTiO3/EuTiO3 interface

   https://doi.org/10.1063/1.5025169  

   Ahadi, Kaveh; Kim, Honggyu; Stemmer, Susanne (May 2018, APL Materials)

   Magnetotransport and magnetism of epitaxial SmTiO3/EuTiO3 heterostructures grown by molecular beam epitaxy are investigated. It is shown that the polar discontinuity at the interface introduces ∼3.9 × 1014 cm−2 carriers into the EuTiO3. The itinerant carriers exhibit two distinct contributions to the spontaneous Hall effect. The anomalous Hall effect appears despite a very small magnetization, indicating a non-collinear spin structure, and the second contribution resembles a topological Hall effect. Qualitative differences exist in the temperature dependence of both Hall effects when compared to uniformly doped EuTiO3. In particular, the topological Hall effect contribution appears at higher temperatures and the anomalous Hall effect shows a sign change with temperature. The results suggest that interfaces can be used to tune topological phenomena in itinerant magnetic systems. 

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3. Giant topological Hall effect in centrosymmetric tetragonal Mn2−xZnxSb

   Md Rafique Un Nabi, Aaron Wegner (November 2021, Physical review)

   Topological magnetism typically appears in noncentrosymmetric compounds or compounds with geometric frustration. Here, we report the effective tuning of magnetism in centrosymmetric tetragonal Mn2−xZnxSb by Zn substitution. The magnetism is found to be closely coupled to the transport properties, giving rise to a very large topological Hall effect with fine-tuning of Zn content, which even persists to high temperature (∼250K). The further magnetoentropic analysis suggests that the topological Hall effect is possibly associated with topological magnetism. Our finding suggests Mn2−xZnxSb is a candidate material for a centrosymmetric tetragonal topological magnetic system, offering opportunities for studying and tuning spin textures and developing near room temperature spin-based devices. 

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4. Weighing Dirac fermions by nonlinear Hall effect

   Wang, Yang; Mambakkam, Sivakumar V.; Law, Stephanie A.; Xiao, John. Q. (March 2022, ArXivorg)

   Breaking the time-reversal symmetry on the surface of a topological insulator can open a gap for the linear dispersion and make the Dirac fermions massive. This can be achieved by either doping a topological insulator with magnetic elements or proximity-coupling it to magnetic insulators. While the exchange gap can be directly imaged in the former case, measuring it at the buried magnetic insulator/topological insulator interface remains to be challenging. Here, we report the observation of a large nonlinear Hall effect in iron garnet/Bi2Se3 heterostructures. Besides illuminating its magnetic origin, we also show that this nonlinear Hall effect can be utilized to measure the size of the exchange gap and the magnetic-proximity onset temperature. Our results demonstrate the nonlinear Hall effect as a spectroscopic tool to probe the modified band structure at magnetic insulator/topological insulator interfaces. 

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5. 1/4 is the new 1/2 when topology is intertwined with Mottness

   https://doi.org/10.1038/s41467-023-41465-6  

   Mai, Peizhi; Zhao, Jinchao; Feldman, Benjamin E; Phillips, Philip W (December 2023, Nature Communications)

   Abstract In non-interacting systems, bands from non-trivial topology emerge strictly at half-filling and exhibit either the quantum anomalous Hall or spin Hall effects. Here we show using determinantal quantum Monte Carlo and an exactly solvable strongly interacting model that these topological states now shift to quarter filling. A topological Mott insulator is the underlying cause. The peak in the spin susceptibility is consistent with a possible ferromagnetic state atT = 0. The onset of such magnetism would convert the quantum spin Hall to a quantum anomalous Hall effect. While such a symmetry-broken phase typically is accompanied by a gap, we find that the interaction strength must exceed a critical value for this to occur. Hence, we predict that topology can obtain in a gapless phase but only in the presence of interactions in dispersive bands. These results explain the recent quarter-filled quantum anomalous Hall effects seen in moiré systems. 

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