Spin interference of holes in silicon nanosandwiches

Spin-dependent transport of holes is studied in silicon nanosandwiches on an $n$-Si (100) surface which are represented by ultranarrow $p$-Si quantum wells confined by $\delta$-barriers heavily doped with boron. The measurement data of the longitudinal and Hall voltages as functions of the top gate voltage without an external magnetic field show the presence of edge conduction channels in the silicon nanosandwiches. An increase in the stabilized source-drain current within the range 0.25–5 nA subsequently exhibits the longitudinal conductance value 4e$^2$/$h$, caused by the contribution of the multiple Andreev reflection, the value 0.7(2e$^2$/$h$) corresponding to the known quantum conductance staircase feature, and displays Aharonov–Casher oscillations, which are indicative of the spin polarization of holes in the edge channels. In addition, at a low stabilized source-drain current, due to spin polarization, a nonzero Hall voltage is detected which is dependent on the top gate voltage; i. e., the quantum spin Hall effect is observed. The measured longitudinal I–V characteristics demonstrate Fiske steps and a negative differential resistance caused by the generation of electromagnetic radiation as a result of the Josephson effect. The results obtained are explained within a model of topological edge states which are a system of superconducting channels containing quantum point contacts transformable to single Josephson junctions at an increasing stabilized source-drain current.