SPIN AND CHARGE TRANSPORT IN 2D MATERIALS AND VAN DER WAALS HETEROSTRUCTURES

Abstract

This thesis focuses on the exploration of topological superconductivity in 2D materials and van der Waals heterostructures. Our approach is to realize topological superconductivity in Ising superconductors. A survey of different candidate materials systems for topological superconductivity is presented in this report. We will show that the Ising superconductor approach has many advantages over the forerunner approach — semiconductor/superconductor heterostructure. Preliminary results on a Ising superconductor NbSe2 are presented. Firstly, 2D superconductivity in ultra-thin NbSe2 is verified by fluctuation effects, square root dependence of in-plane upper critical field as well as BKT transition. Secondly, spin-polarized tunnel spectroscopy of NbSe2 is presented. The tunnel spectra strongly depend on the magnetization configuration of the tunnel contacts. The result is drastically different from a similar experiment on aluminium, suggesting the existence of spin supercurrent carried by spin-triplet Cooper pairs in NbSe2. Last but not least, the existence of spin supercurrent is further supported by non-local spin valve measurement. A clear spin signal of magnitude up to 4 Ω was observed. Spin lifetime and diffusion length were extracted from Hanle precession measurement to be 220 ps and 1.81 μm, respectively.