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TT: Fachverband Tiefe Temperaturen

TT 57: Topology: Poster

TT 57.3: Poster

Mittwoch, 20. März 2024, 15:00–18:00, Poster E

Nearly perfectly compensated Topological Insulator Bi_1.08Sn_0.02Sb_0.9Te₂S without charge puddles? — •Rajendra Loke, Rohit Sharma, Mahasweta Bagchi, Yongjian Wang, Yoichi Ando, Thomas Lorenz, and Joachim Hemberger — Physics Institute II, University of Cologne, Zülpicher Straße 77, D-50937 Cologne, Germany.

In topological insulators the bulk conductivity can successfully be suppressed by compensation doping. However, fluctuations of the Coulomb potential usually lead to the formation of mesoscopic charge puddles, which strongly influence the transport properties as magnetic fields may generate a percolating path for conductivity. But even in the non-percolating case, the high DC-resistivity can be overcome at high enough frequencies. The cut-off frequency ν_c, for which AC-conductivity sets in, is related the puddle size and may be located in the microwave regime. The value of ν_c is magnetic field dependent, giving rise to a large positive magnetoconductivity in the gigahertz range [1]. Here we present impedance spectroscopy measurements on various TI systems. While e.g. BiSbTeSe₂ (BSTS) shows large positive magneto-conductivity in the GHz range due to the increase of the puddle size in magnetic field, the system Bi_1.08Sn_0.02Sb_0.9Te₂S (Sn-BSTS) only exhibits the Weak Anti-localization effect, a signature of the surface states of Dirac materials, associated with negative magneto-conductivity. Therefore, in Sn-BSTS does not show any signature of puddle formation (in the frequency range measured so far).

Keywords: Topological Insulator; Charge Puddles; Gigahertz; Magnetoconductivity