Imaging the topological sign of a Dirac mass with spin-polarized tunneling
Abstract
A Dirac mass is characterized not only by its magnitude but also by its sign, which influences the Berry curvature, Hall response, and the propagation direction of chiral boundary modes. However, local spectroscopy of magnetic topological surfaces has so far accessed only the gap magnitude |M|. Here we show how the topological sign of M can be determined locally. We first establish the sign information that spin-resolved tunneling can access and the reference required to obtain an absolute Hall sign. Although spin--orbital entanglement generally obscures the relation between measured spin and Dirac pseudospin, crystalline rotation symmetry alleviates this ambiguity at the band edge. On a C3 axis, an axial tip couples to a fully spin-polarized state whose tunneling asymmetry directly reveals the sign of the occupied-band Berry curvature, independent of orbital composition. We further show that the zeroth Landau level provides an independent mass-sign measurement with an unpolarized tip, while opposite domains and their chiral domain-wall modes provide self-consistency checks. These results pave the way for imaging the locations where the topological character changes within a material, rather than merely identifying where a spectral gap appears.
Related
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BibTeX
@misc{kazemikhah2026imaging,
title = {{Imaging the topological sign of a Dirac mass with spin-polarized tunneling}},
author = {Payman Kazemikhah and Ruolun Zhang and Byunghoon Kim and Xiangyu Luo and Zachary Ducorsky and Yu-Peng Zhu and Md. Shafayat Hossain and M. Zahid Hasan},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.17464},
eprint = {2610.17464},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.17464},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Imaging the topological sign of a Dirac mass with spin-polarized tunneling
AU - Payman Kazemikhah
AU - Ruolun Zhang
AU - Byunghoon Kim
AU - Xiangyu Luo
AU - Zachary Ducorsky
AU - Yu-Peng Zhu
AU - Md. Shafayat Hossain
AU - M. Zahid Hasan
PY - 2026
DA - 2026/10/12
PB - arXiv
DO - 10.48550/arxiv.2610.17464
UR - https://arxiv.org/abs/2610.17464
AB - A Dirac mass is characterized not only by its magnitude but also by its sign, which influences the Berry curvature, Hall response, and the propagation direction of chiral boundary modes. However, local spectroscopy of magnetic topological surfaces has so far accessed only the gap magnitude |M|. Here we show how the topological sign of M can be determined locally. We first establish the sign information that spin-resolved tunneling can access and the reference required to obtain an absolute Hall sign. Although spin--orbital entanglement generally obscures the relation between measured spin and Dirac pseudospin, crystalline rotation symmetry alleviates this ambiguity at the band edge. On a C_3 axis, an axial tip couples to a fully spin-polarized state whose tunneling asymmetry directly reveals the sign of the occupied-band Berry curvature, independent of orbital composition. We further show that the zeroth Landau level provides an independent mass-sign measurement with an unpolarized tip, while opposite domains and their chiral domain-wall modes provide self-consistency checks. These results pave the way for imaging the locations where the topological character changes within a material, rather than merely identifying where a spectral gap appears.
ER -