Superconductivity in silicon nanostructures

We present the findings of the superconductivity observed in the silicon nanostructures prepared by short time diffusion of boron on the n-type Si(100) surface. These Si-based nanostructures represent the p-type ultra-narrow self-assembled silicon quantum wells, 2nm, confined by the delta - barriers heavily doped with boron, 3nm. The EPR and the thermo-emf studies show that the delta - barriers appear to consist of the trigonal dipole centres, which are caused by the negative-U reconstruction of the shallow boron acceptors. Using the CV and thermo-emf techniques, the transport of two-dimensional holes inside SQW is demonstrated to be accompanied by single-hole tunneling through these negative-U centres that results in the superconductivity of the delta - barriers. The values of the correlation gaps obtained from these measurements are in a good agreement with the data derived from the temperature and magnetic field dependencies of the magnetic susceptibility, which reveal a strong diamagnetism and additionally identify the superconductor gap value.Comment: 4 pages, 6 figures, presented at the 4th International Conference on Vortex Matter in Superconductors, Crete, Greece, September 3-9, 200

Decay of nuclear hyperpolarization in silicon microparticles

We investigate the low-field relaxation of nuclear hyperpolarization in undoped and highly doped silicon microparticles at room temperature following removal from high field. For nominally undoped particles, two relaxation time scales are identified for ambient fields above 0.2 mT. The slower, T_1s, is roughly independent of ambient field; the faster, T_1f, decreases with increasing ambient field. A model in which nuclear spin relaxation occurs at the particle surface via a two-electron mechanism is shown to be in good agreement with the experimental data, particularly the field-independence of T_1s. For boron-doped particles, a single relaxation time scale is observed. This suggests that for doped particles, mobile carriers and bulk ionized acceptor sites, rather than paramagnetic surface states, are the dominant relaxation mechanisms. Relaxation times for the undoped particles are not affected by tumbling in a liquid solution.Comment: related papers at http://marcuslab.harvard.ed

Magnetic resonance spectroscopy of single centers in silicon quantum wells

We present the new optically-detected magnetic resonance (ODMR) technique which reveals single point defects in silicon quantum wells embedded in microcavities within frameworks of the excitonic normal-mode coupling (NMC) without the external cavity and the hf source.Comment: 8 pages, 7 figure

Spin transport in mesoscopic rings with inhomogeneous spin-orbit coupling

We revisit the problem of electron transport through mesoscopic rings with spin-orbit (SO) interaction. In the well-known path-integral approach, the scattering states for a quasi-1D ring with quasi-1D leads can be expressed in terms of spinless electrons subject to a fictitious magnetic flux. We show that spin-dependent quantum-interference effects in small rings are strongest for spatially inhomogeneous SO interactions, in which case spin currents can be controlled by a small external magnetic field. Mesoscopic spin Hall effects in four-terminal rings can also be understood in terms of the fictitious magnetic flux.Comment: 5 pages, 2 figure

Three small systems showing probable room-temperature superconductivity

I shall discuss three small systems in which I think room-temperature superconductivity has been observed. These are: 1. Narrow channels through films of oxidised atactic polypropylene (OAPP) and other polymers. 2. Some multiwalled carbon nanotubes or mats of nanotubes. 3. Sandwich structures based on CdF_2. The main emphasis will be on polymer films.Comment: 8 pages. Physica C, to be published. Changes from v2: Journal of publication added. Two sentences added on both page 1 and page 6. Three references adde

EDEPR of impurity centers embedded in silicon microcavities

We present the first findings of the new electrically-detected EPR (EDEPR) technique which reveal different shallow and deep centers without using the external cavity as well as the hf source and recorder, with measuring the only magnetoresistance of the Si-QW confined by the superconductor delta-barriers.Comment: 7 pages, 7 figure

Spin Depolarization in Quantum Wires Polarized Spontaneously in a Zero Magnetic Field

The conditions for a spontaneous spin polarization in a quantum wire positioned in a zero magnetic field are analyzed under weak population of one-dimensional subbands that gives rise to the efficient quenching of the kinetic energy by the exchange energy of carriers. The critical linear concentration of carriers above which the quasi one-dimensional gas undergoes a complete spin depolarization is determined by the Hartree-Fock approximation. The dependence of the critical linear concentration on the concentration of carriers is defined to reveal the interplay of the spin depolarization with the evolution of the 0.7 (2e2/h) feature in the quantum conductance staircase from the e2/h to 3/2 (e2/h) values. This dependence is used to study the effect of the hole concentration on the 0.7 (2e2/h) feature in the quantum conductance staircase of the quantum wire prepared inside the p-type silicon quantum well using the split-gate technique. The 1D channel is demonstrated to be spin-polarized at the linear concentration of holes lower than the critical linear concentration, because the 0.7 (2e2/h) feature is close to the value of 0.5 (2e2/h) that indicates the spin degeneracy lifting for the first step of the quantum conductance staircase. The 0.7 (2e2/h) feature is found to take however its normal magnitude when the linear concentration of holes attains the critical value corresponding to the spin depolarization. The variations in the height of the 0.7 (2e2/h) feature observed in the hole quantum conductance staircase that is revealed by the p-type silicon quantum wire seem to be related to the evidences of the quantum conductance staircase obtained by varying the concentration of electrons in the 1D channel prepared inside the GaAs-AlGaAs heterojunction.Comment: 27 pages, 5 figure