Spin transistor and quantum spin Hall-effects in CdBxF2−x-p-CdF2-CdBxF2−x sandwich nanostructures

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 δ-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 δ-barriers. The value of the superconductor energy gap, 2Δ = 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, πΔ/e, 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.