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

T. Guillet (1) , Alain Marty (1) , C. Beigne (1) , Céline Vergnaud (1) , M-T Dau (1) , P. Noel (1) , J. Frigerio (2) , G. Isella (2) , M. Jamet (1)

1 SPINTEC - SPINtronique et TEchnologie des Composants
2 POLIMI - Politecnico di Milano [Milan]

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.

Domains: Condensed Matter [cond-mat]

T. Guillet, Alain Marty, C. Beigne, Céline Vergnaud, M-T Dau, et al.. Magnetotransport in Bi$_2$ Se$_3$ thin films epitaxially grown on Ge(111). AIP Advances, 2018, 8 (11), pp.115125. ⟨10.1063/1.5048547⟩. ⟨cea-02044793⟩