Interfacial superconductivity in bilayer and multilayer IV–VI semiconductor heterostructures

Abstract

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⩽6.5K 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.

Effect of activation volume on the defect-induced superconductivity in semiconducting superlattices

“…It appears that the SC is not in the deposited layer but is in a region which includes the PbTe surface (much more earlier Strongin et al measured the critical field at which SC nucleates on the surface of Pb doped with Bi [8]). Recent progresses about superconducting layers (or interfaces) in PbTe/PbS SL could be traced in [9][10][11][12][13][14]. From 1996 till 2008 Fogel et al published a series of articles that provided most of the details we know about the SC in chalcogenide superlattices [10][11][12][13][14].…”

“…The lattice mismatch between different compounds varies from 2% between PbTe and SnTe to 13% in the PbTe/YbS system. The defects formed in interfaces (SLs) are crucial to the observed superconductivity [9][10][11][12][13][14]. Based on this concern, in this short paper, we shall adopt the quantum chemistry approach [17][18][19][20] to investigate the defect(vacancy or hole)-induced SC considering especially previous measurements about PbTe/PbS SLs [13].…”

“…To be specific, heterostructures reveal the superconducting transitions with high critical temperatures (6-7 K), though they contain only non-doped semiconducting materials. The main condition, as proposed in [2,[10][11][12][13][14], for their superconductivity is the dislocation grid on the interface. Therefore, in this situation the superconductivity is interfacial.…”

“…Recent progresses about superconducting layers (or interfaces) in PbTe/PbS SL could be traced in [9][10][11][12][13][14]. From 1996 till 2008 Fogel et al published a series of articles that provided most of the details we know about the SC in chalcogenide superlattices [10][11][12][13][14]. To be specific, heterostructures reveal the superconducting transitions with high critical temperatures (6-7 K), though they contain only non-doped semiconducting materials.…”

“…However, as briefly introduced above, structural distortions and chemical doping in complicated compounds play important role for the onset of SC. The most interesting question is about the origin of possible defect-induced SC in above mentioned semiconducting multilayers (interfaces) consisting only of semiconducting materials [9][10][11][12][13][14].…”