Spin Transport and Quantum Phase Changes in Pb_0.24Sn_0.76Te/Graphene Heterostructures

Heterostructures of novel materials such as topological insulators and two-dimensional (2D) materials possess several unique characteristics, including spin momentum locking, high spin-orbit coupling, and susceptibility to proximity effects, making them ideal for use in devices for future computing. We recently demonstrated this in Pb_0.24Sn_0.76Te/graphene (PST/Gr), where the heterostructure mobility is nearly twice that of either constituent Pb_0.24Sn_0.76Te or graphene.¹ In this work, we fabricate and measure non-local spin valves on a PST/Gr heterostructure and find spin lifetimes and spin polarization efficiencies of 300 ps and 12%, respectively. We identify a spin-split two-dimensional electron gas (2DEG) at the PST/Gr interface as well as a quantum phase change occurring at 40 K. Below this transition temperature, the non-local resistance exhibits metallic behavior as the 2DEG dominates the device operation, whereas in the high-temperature regime we observe semiconducting behavior. The PST/Gr spin valve is robust, showing no signs of performance decay in ambient conditions and operating up to 500 K. Quantum phase transitions such as these could provide a low-power switching mode for novel electronic devices in future computing platforms.

¹ G.M. Stephen et al. (2022) ACS Nano, doi: 10.1021/acsnano.2c08911