Negative-U Centers as a Basis of Topological Edge Channels

We present the findings of the studies of the silicon sandwich nanostructure that represents the high mobility ultranarrow silicon quantum well of the p-type (Si-QW), 2 nm, confined by the delta-barriers, 3 nm, heavily doped with boron on the ntype Si (100) surface. The ESR studies show that nanostructured delta-barriers confining the Si-QW consist predominantly of the dipole negative-U centers of boron, which are caused by the reconstruction of the shallow boron acceptors along the < 111 > crystallographic axis, 2B(0). B+ + B-. The electrically ordered chains of dipole negative-U centers of boron in the d-barriers appear to give rise to the topological edge states separated vertically, because the value of the longitudinal, G(xx) = 4e(2)/h, and transversal, G(xy) = e(2)/h, conductance measured at extremely low drain-source current indicates the exhibition of the Quantum Spin Hall effect. Besides, the Aharonov-Casher conductance oscillations and the "0.7 center dot (2e(2)/h)-feature" obtained are evidence of the interplay of the spontaneous spin polarisation and the Rashba spin-orbit interaction that is attributable to the formation of the topological edge channels. We discuss the phenomenological model of the topological edge channel which can demonstrate the ballistic, Aharonov-Chasher effect or Josephson junction behaviour in dependence on the disorder in the distribution of the negative-U dipole centers in the upper and down delta-barriers.