Superconducting properties of silicon nanostructures

Superconducting properties of silicon sandwich nanostructures on the n-Si (100) surface, which represent the ultra-narrow p-type silicon quantum wells confined by heavily boron-doped δ barriers, manifest themselves in the measurements of the temperature and field dependences of resistivity, thermopower, heat capacity, and static magnetic susceptibility. The cyclotron-resonance, scanning-tunneling-microscopy, and ESR data identify the presence of the single trigonal negative-U dipole boron centers in nanostructured δ barriers B +-,B −, which are formed due to the reconstruction of shallow boron acceptors, 2B 0 ⇒ B + + B −. The obtained results indicate that these negative-U centers are responsible for the transport of small-radius hole bipolarons, which is likely the basis of the mechanism of high-temperature superconductivity with T C = 145 K. The superconductor-gap value of 0.044 eV determined from the measurements of the critical temperature using the above techniques is almost identical to the data on the tunneling spectroscopy and direct record of tunneling I–V characteristics. The quantization of the superconductive characteristics for silicon sandwich nanostructures manifests itself in the temperature and field dependences of the heat capacity and static magnetic susceptibility, which show the oscillations of the second critical field and critical temperature arising due to the supercurrent quantization.

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