Topological Surface Charge Detection via Terahertz Time-domain Spectroscopy
Abstract
The topological magnetoelectric effect (TME) is a condensed-matter realization of the four-dimensional quantum Hall effect (4D-QHE), manifesting as quantized surface charge accumulation proportional to an applied magnetic field. To date, however, no optical technique has been developed to directly probe this charge accumulation. Here, we demonstrate a terahertz time-domain spectroscopy method for direct detection of surface charge accumulation---a physical quantity relevant to both the 4D-QHE and 2D-QHE, in sharp contrast to the previous optical measurements, which focused on the Hall conductivity σxy of the 2D-QHE. Using a chromium-doped (Bi,Sb)2Te3 thin film, we achieve sub-milliradian Faraday rotation precision. Extending this scheme to axion insulators, we predict that the TME gives rise to an imaginary Faraday rotation linear in frequency, whose slope directly reflects the single-surface charge density. With further improvements in sample thickness and precision, this approach offers a viable pathway toward direct verification of the TME and 4D-QHE.
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BibTeX
@misc{shen2026topological,
title = {{Topological Surface Charge Detection via Terahertz Time-domain Spectroscopy}},
author = {Tong Shen and Yiyang Xie and Yucheng Dai and Yifan Zhang and Yuanze Li and Xufeng Kou and Tian Liang},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2606.15371},
eprint = {2606.15371},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.15371},
}
RIS
TY - UNPB
TI - Topological Surface Charge Detection via Terahertz Time-domain Spectroscopy
AU - Tong Shen
AU - Yiyang Xie
AU - Yucheng Dai
AU - Yifan Zhang
AU - Yuanze Li
AU - Xufeng Kou
AU - Tian Liang
PY - 2026
DA - 2026/09/13
PB - arXiv
DO - 10.48550/arxiv.2606.15371
UR - https://arxiv.org/abs/2606.15371
AB - The topological magnetoelectric effect (TME) is a condensed-matter realization of the four-dimensional quantum Hall effect (4D-QHE), manifesting as quantized surface charge accumulation proportional to an applied magnetic field. To date, however, no optical technique has been developed to directly probe this charge accumulation. Here, we demonstrate a terahertz time-domain spectroscopy method for direct detection of surface charge accumulation---a physical quantity relevant to both the 4D-QHE and 2D-QHE, in sharp contrast to the previous optical measurements, which focused on the Hall conductivity σ_xy of the 2D-QHE. Using a chromium-doped (Bi,Sb)_2Te_3 thin film, we achieve sub-milliradian Faraday rotation precision. Extending this scheme to axion insulators, we predict that the TME gives rise to an imaginary Faraday rotation linear in frequency, whose slope directly reflects the single-surface charge density. With further improvements in sample thickness and precision, this approach offers a viable pathway toward direct verification of the TME and 4D-QHE.
ER -