Momentum-space and real-space Berry curvatures in Mn$_{3}$Sn

Mn_{3}3X (X= Sn, Ge) are noncollinear antiferromagnets hosting a large anomalous Hall effect (AHE). Weyl nodes in the electronic dispersions are believed to cause this AHE, but their locus in the momentum space is yet to be pinned down. We present a detailed study of the Hall conductivity tensor and magnetization in Mn_{3}3Sn crystals and find that in the presence of a moderate magnetic field, spin texture sets the orientation of the kk-space Berry curvature with no detectable in-plane anisotropy due to the Z_6Z6 symmetry of the underlying lattice. We quantify the energy cost of domain nucleation and show that the multidomain regime is restricted to a narrow field window. Comparing the field dependence of AHE and magnetization, we find that there is a distinct component in the AHE which does not scale with magnetization when the domain walls are erected. This so-called ‘topological’ Hall effect provides indirect evidence for a non-coplanar spin components and real-space Berry curvature in domain walls.

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Manipulating Berry curvature of SrRuO3 thin films via epitaxial strain

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2101946118 ◽

2021 ◽

Vol 118 (18) ◽

pp. e2101946118

Author(s):

Di Tian ◽

Zhiwei Liu ◽

Shengchun Shen ◽

Zhuolu Li ◽

Yu Zhou ◽

...

Keyword(s):

Thin Films ◽

Hall Effect ◽

Anomalous Hall Effect ◽

Real Space ◽

Electronic Band ◽

Berry Curvature ◽

Hall Resistivity ◽

Epitaxial Strain ◽

Wide Range ◽

Quantum Materials

Berry curvature plays a crucial role in exotic electronic states of quantum materials, such as the intrinsic anomalous Hall effect. As Berry curvature is highly sensitive to subtle changes of electronic band structures, it can be finely tuned via external stimulus. Here, we demonstrate in SrRuO3 thin films that both the magnitude and sign of anomalous Hall resistivity can be effectively controlled with epitaxial strain. Our first-principles calculations reveal that epitaxial strain induces an additional crystal field splitting and changes the order of Ru d orbital energies, which alters the Berry curvature and leads to the sign and magnitude change of anomalous Hall conductivity. Furthermore, we show that the rotation of the Ru magnetic moment in real space of a tensile-strained sample can result in an exotic nonmonotonic change of anomalous Hall resistivity with the sweeping of magnetic field, resembling the topological Hall effect observed in noncoplanar spin systems. These findings not only deepen our understanding of anomalous Hall effect in SrRuO3 systems but also provide an effective tuning knob to manipulate Berry curvature and related physical properties in a wide range of quantum materials.

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Interface-induced sign reversal of the anomalous Hall effect in magnetic topological insulator heterostructures

Nature Communications ◽

10.1038/s41467-020-20349-z ◽

2021 ◽

Vol 12 (1) ◽

Cited By ~ 1

Author(s):

Fei Wang ◽

Xuepeng Wang ◽

Yi-Fan Zhao ◽

Di Xiao ◽

Ling-Jie Zhou ◽

...

Keyword(s):

Hall Effect ◽

Electric Fields ◽

First Principles ◽

Berry Phase ◽

Condensed Matter ◽

Anomalous Hall Effect ◽

First Principles Calculations ◽

Sign Reversal ◽

Berry Curvature ◽

Topological Materials

AbstractThe Berry phase picture provides important insights into the electronic properties of condensed matter systems. The intrinsic anomalous Hall (AH) effect can be understood as the consequence of non-zero Berry curvature in momentum space. Here, we fabricate TI/magnetic TI heterostructures and find that the sign of the AH effect in the magnetic TI layer can be changed from being positive to negative with increasing the thickness of the top TI layer. Our first-principles calculations show that the built-in electric fields at the TI/magnetic TI interface influence the band structure of the magnetic TI layer, and thus lead to a reconstruction of the Berry curvature in the heterostructure samples. Based on the interface-induced AH effect with a negative sign in TI/V-doped TI bilayer structures, we create an artificial “topological Hall effect”-like feature in the Hall trace of the V-doped TI/TI/Cr-doped TI sandwich heterostructures. Our study provides a new route to create the Berry curvature change in magnetic topological materials that may lead to potential technological applications.

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