Dresden 2026 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 61: Topology – Poster

TT 61.2: Poster

Wednesday, March 11, 2026, 15:00–17:00, P4

Investigating Electrical and Thermal Hall Effect in Topological Insulators — •Karan Singh, Rohit Sharma, Yongjan Wang, Yoichi Ando, Achim Rosch, and Thomas Lorenz — II. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, D-50937 Köln, Germany

3D topological insulators are characterized by a bulk band gap and topologically protected gapless surface states formed by massless Dirac fermions. However, chemical disorder produces spatially fluctuating electric potentials, forming "charge puddles" that allow current to flow through the bulk [1]. With decreasing temperature, charge puddles localize, turning the sample electrically insulating. But these charge puddles remain thermally coupled via phonons and can be probed by the thermal Hall transport measurements [2]. In this work, we grew single crystals of TlBi_0.3Sb_0.7Te₂ and performed electrical and thermal transport measurements. The material shows a metal-semiconductor transition near 100 K and electron-like carriers at all temperatures. Notably, the thermal Hall conductivity (k_xy) measured on the same sample deviates from the Wiedemann-Franz law. After subtracting the electronic thermal contribution, the residual thermal Hall signal indicates that heat transport in this system involves contributions beyond conventional electronic carriers.

Work supported by the German Research Foundation via Project No. 277146847-CRC1238 (Subprojects A02 and B01).

[1] O. Breunig et al., Nat. Comm. 8, 15545 (2017).

[2] R. Sharma et al., Phys. Rev. B 109, 104304 (2024).

Keywords: Topological insulator; Single-crystal growth; Defects; Electrical transport; Thermal Hall effect