Spin-orbit coupling, superconductivity, and topological states in Sb2Te3-GeTe-based heterostructures

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• Dr. Vijay Narayan (University of Cambridge)
• Monday 15 February 2016, 14:15-15:15
• Mott Seminar Room (Mott Building Room 531), Cavendish Laboratory.

If you have a question about this talk, please contact Teri Bartlett.

Spin-orbit coupling, superconductivity, and topological states Sb2Te3 GeTe-based heterostructures. GeTe is a narrow band gap semiconductor that goes superconducting at low temperatures and additionally, due to its non-centrosymmetric unit cell, has a strong spin-orbit field. Thus GeTe is a single-phase material which is very likely to host p-wave superconductivity. I will first present magneto-transport measurements on Hall bars of molecular beam epitaxy (MBE)-grown thin films of GeTe [1] which are on the brink of superconductivity. The experimental data show several novel and intriguing characteristics which arise from the interplay of the spin-orbit field and superconducting correlations. First, the weak anti-localisation (WAL) behaviour below ≈ 2 K suggests the role of two-dimensional (2D) rather than bulk conducting states. Second, at even lower temperatures ≈ 0.3 K the impending superconductivity affects both the longitudinal and Hall components of resistivity: the former is seen to deviate from the Hikami-Larkin-Nagaoka (HLN) form [2], and the latter develops a perceptible reduction about zero field. And third, the in-plane field magnetoresistance shows a novel and unexplained hysteretic behaviour, which vanishes at 0.7 K. These data offer new insights into the physics underlying spin-orbit coupled superconductors. The second part of my talk will focus on MBE -grown multilayers of GeTe and the topological insulator Sb2Te3 [3] above the superconducting transition of GeTe. The temperature and magnetic field-dependent electrical characteristics of the multilayers strongly suggest that transport is confined to the Sb2Te3-GeTe interfaces. Remarkably, we find that Sb2Te3-GeTe-Sb2Te3 can either have one 2D mode or three depending on the precise layer structure. We present experimental evidence suggesting that the intervening GeTe layer has an important role in deciding the ultimate number of 2D states. Our data suggest, therefore, that the GeTe-Sb2Te3 system is a promising platform to realise topological insulator multilayers, and thus towards explorations of exotic topological phases. [1] V. Narayan, T.-A. Nguyen, R. Mansell, D. A. Ritchie and G. Mussler (Phys. Status Solidi – RRL , 2016 DOI : 10.1002/pssr.201510430 [2] S. Hikami, A. I. Larkin, Y. Nagaoka, Prog. Theor. Phys. 1980, 63, 707. [3] T.-A. Nguyen, D. Backes, A. Singh, R. Mansell, C. Barnes, D. A. Ritchie, G. Mussler, M. Lanius, D.Grützmacher and V. Narayan (in preparation).

This talk is part of the Semiconductor Physics Group Seminars series.

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