We present the findings of the 0.7·(2e 2 /h) feature in the hole quantum conductance staircase that is caused by silicon one-dimensional channels prepared by the split-gate method inside the p-type silicon quantum well (SQW) on the n-type Si (100) surface. Firstly, the interplay of the spin depolarisation with the evolution of the 0.7·(2e 2 /h) feature from the e 2 /h to 3/2 e 2 /h values as a function of the sheet density of holes is revealed by the quantum point contact connecting two 2D reservoirs in the p-type SQW. The 1D holes are demonstrated to be spin-polarised at low sheet density, because the 0.7·(2e 2 /h) feature is close to the value of 0.5·(2e 2 /h) that indicates the spin degeneracy lifting for the first step of the quantum conductance staircase. The 0.7·(2e 2 /h) feature is found to take however the value of 0.75·(2e 2 /h) when the sheet density increases thereby giving rise to the spin depolarisation of the 1D holes. Secondly, the amplitude and phase sensitivity of the 0.7·(2e 2 /h) feature are studied by varying the value of the external magnetic field and the top gate voltage that are applied perpendicularly to the plane of the double-slit ring embedded in the p-type SQW, with the extra quantum point contact inserted in the one of its arms. The Aharonov-Bohm (AB) and the Aharonov-Casher (AC) conductance oscillations obtained are evidence of the interplay of the spontaneous spin polarisation and the Rashba spin-orbit interaction (SOI) in the formation of the 0.7·(2e 2 /h) feature. Finally, the variations of the 0.7·(2e 2 /h) feature caused by the Rashba SOI are found to take in the fractional form with both the plateaux and steps as a function of the top gate voltage. IntroductionProgress in semiconductor nanotechnology makes it possible to fabricate clean one-dimensional (1D) constrictions with low density of high-mobility charge carriers, which exhibit ballistic behavior if the mean free path is longer than the channel length [1][2][3][4][5][6][7][8]. Therefore, the conductance of such quantum wires prepared by the split-gate [1-7] and cleaved edge overgrowth [8] methods depends only on the transmission coefficient, T [9, 10]:

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We present the findings of the superconductivity in the silicon nanostructures prepared by short time diffusion of boron after preliminary oxidation of the n-type Si (100) surface. These Si-based nanostructures represent the p-type high mobility silicon quantum well (Si-QW) confined by the δ-barriers heavily doped with boron. The ESR studies show that the δ-barriers appear to consist of the trigonal dipole centers, B +-B-, which are caused by the negative-U reconstruction of the shallow boron acceptors, 2B 0 → B + + B-. The temperature and magnetic field dependencies of the resistance, thermo-emf, specific heat and magnetic susceptibility demonstrate that the high temperature superconductivity observed seems to result from the transfer of the small hole bipolarons through these negative-U dipole centers of boron at the Si-QW-δ-barrier interfaces. The value of the superconductor energy gap obtained is in a good agreement with the data derived from the oscillations of the conductance in normal state and of the zero-resistance supercurrent in superconductor state as a function of the bias voltage. These oscillations appear to be correlated by on-and off-resonance tuning the two-dimensional subbands of holes with the Fermi energy in the superconductor δ-barriers. Finally, the proximity effect in the S-Si-QW-S structure is revealed by the findings of the multiple Andreev reflection (MAR) processes and the quantiza-tion of the supercurrent.

The negative-U impurity stripes confining the edge channels of semiconductor quantum wells are shown to allow the effective cooling inside in the process of the spin-dependent transport. The aforesaid promotes also the creation of composite bosons and fermions by the capture of single magnetic flux quanta on the edge channels under the conditions of low sheet density of carriers, thus opening new opportunities for the registration of the quantum kinetic phenomena in weak magnetic fields at high temperatures up to the room temperature. As a certain version noted above we present the first findings of the high temperature de Haasvan Alphen, 300K, and quantum Hall, 77K, effects in the silicon sandwich structure that represents the ultra-narrow, 2 nm, p-type quantum well (Si-QW) confined by the delta barriers heavily doped with boron on the n-type Si (100) surface. These data appear to result from the low density of single holes that are of small effective mass in the edge channels of p-type Si-QW because of the impurity confinement by the stripes consisting of the negative-U dipole boron centers which seems to give rise to the efficiency reduction of the electron-electron interaction.