Magnetotransport in Bi$_2$ Se$_3$ thin films epitaxially grown on Ge(111)

Abstract : Topological insulators (TIs) like Bi$_2$Se$_3$ are a class of material with topologically protected surface states in which spin-momentum locking may enable spin-polarized and defect-tolerant transport. In this work, we achieved the epitaxial growth of Bi$_2$Se$_3$ thin films on germanium, which is a key material for microelectronics. Germanium also exhibits interesting properties with respect to the electron spin such as a spin diffusion length of several micrometers at room temperature. By growing Bi$_2$Se$_3$ on germanium, we aim at combining the long spin diffusion length of Ge with the spin-momentum locking at the surface of Bi$_2$Se$_3$. We first performed a thorough structural analysis of Bi$_2$Se$_3$ films using electron and x-ray diffraction as well as atomic force microscopy. Then, magnetotransport measurements at low temperature showed the signature of weak antilocalization as a result of two-dimensional transport in the presence of spinorbit coupling. We interpret our results as the signature of magnetotransport in a single strongly coupled coherent channel in the presence of surface to bulk scattering. Interestingly, the magnetotransport measurements also point out that the conduction channel can be tuned between the Bi$_2$Se$_3$ film and the Ge layer underneath by means of the bias voltage or the applied magnetic field. This result suggests that the Bi$_2$Se$_3$/Ge junction is a promising candidate for tuning spin-related phenomena at interfaces between TIs and semiconductors.
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T. Guillet, Alain Marty, C. Beigne, C. Vergnaud, M-T Dau, et al.. Magnetotransport in Bi$_2$ Se$_3$ thin films epitaxially grown on Ge(111). AIP Advances, American Institute of Physics- AIP Publishing LLC, 2018, 8 (11), pp.115125. ⟨10.1063/1.5048547⟩. ⟨cea-02044793⟩

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