Interface superconductivity in two-layer and multilayer semiconductivity IV-VI heterostructures

A comprehensive investigation and comparison of the superconducting properties of bilayer and multilayer epitaxial heterostructures of IV-VI semiconductors exhibiting superconductivity at critical temperatures Tc 6.5 K is carried out. The superconductivity of these systems is due to inversion of the bands in the narrow-gap semiconductors on account of the nonuniform stresses created by the grids of misfit dislocations arising at the interfaces during the epitaxial growth. It is found that Tc and the character of the superconducting transition of bilayer PbTe/PbS heterostructures depend on the thickness d of the semiconductor layers and are directly related to the quality of the grids of misfit dislocations at the interfaces (the number and type of structural defects in the grids). Substantial differences in the behavior of bilayer sandwiches and superlattices are found. The minimum thickness d at which superconductivity appears is several times larger for bilayer than for multilayer systems. The upper critical magnetic fields Hc2 of the bilayer systems are more anisotropic. For superlattices 3D behavior is observed in the temperature region close to Tc, and with decreasing temperature a 3D-2D crossover occurs. For the bilayer structures 2D behavior starts immediately from Tc, and a 2D-1D crossover is observed, with the sharp divergence of Hc2 that is characteristic of superconducting nets