Spin Transistor and Quantum Spin Hall Effects in CdBxF2-x - p-CdF2 - CdBxF2-x Sandwich Nanostructures

TL;DR

This study investigates spin transistor and quantum spin Hall effects in CdBxF2-x - p-CdF2 - CdBxF2-x nanostructures, revealing high spin polarization and superconducting properties that enable control of quantum states via gate voltage.

Contribution

It presents the first observation of Hall quantum conductance staircase and demonstrates the role of multiple Andreev reflections in spin polarization in these nanostructures.

Findings

High temperature superconductor properties of CdBxF2-x delta-barriers.

Observation of Hall quantum conductance staircase.

Evidence of multiple Andreev reflections influencing spin polarization.

Abstract

Planar CdBxF2-x - p-CdF2 - CdBxF2-x sandwich nanostructures prepared on the surface of the n-type CdF2 bulk crystal are studied to register the spin transistor and quantum spin Hall effects. The current-voltage characteristics of the ultra-shallow p+-n junctions verify the CdF2 gap, 7.8 eV, and the quantum subbands of the 2D holes in the p-type CdF2 quantum well confined by the CdBxF2-x delta-barriers. The temperature and magnetic field dependencies of the resistance, specific heat and magnetic susceptibility demonstrate the high temperature superconductor properties for the CdBxF2-x delta-barriers. The value of the superconductor energy gap, 102.06 meV, determined by the tunneling spectroscopy method appears to be in a good agreement with the relationship between the zero-resistance supercurrent in superconductor state and the conductance in normal state at the energies of the 2D hole subbands. The results obtained are evidence of the important role of the multiple Andreev reflections in the creation of the high spin polarization of the 2D holes in the edged channels of the sandwich device. The high spin hole polarization in the edged channels is shown to identify the mechanism of the spin transistor and quantum spin Hall effects induced by varying the top gate voltage, which is revealed by the first observation of the Hall quantum conductance staircase.