Spatially inhomogeneous discrete states of a superconductor upon injection of nonequilibrium quasiparticles from a point contact with a normal metal

Abstract

The current-voltage characteristics (IVC) of S − c − N point contacts of superconductors with a small coherence length ξ0 reveal steps with discrete values of the differential resistance. This peculiarity is associated with a transition of the contact region of the superconductor to a spatially inhomogeneous state under the influence of the current injection of nonequilibrium quasiparticles penetrating the superconductor to a depth lE . The role of the relaxation of the disbalance between the occupancies of electron-and hole-like branches of the quasiparticle spectrum is manifested in the displacement of the position of the singularities on the IVC towards higher energies upon an increase in the magnetic field and/or temperature. This effect was observed in superconductors with different ratios of the contact diameter d and ξ0 or lE in the series T a (dApparently, a jumplike displacement of the boundary between regions with suppressed and equilibrium values of the energy gap near the contact is responsible for the oscillations observed on the IVC of point contacts between single crystals of high-temperature superconductors (HTS) and a normal metal. The resistance-periodic step-like structure of the IVC allows us to estimate the penetration depth lE of the electric field in N bSe2 and Y BaSrCuO.

"Internal" coherent effects in HTS-normal metal point contacts

“…If this were not so, the oscillation period would gradually approach the value δV = hω/2e 16 µV (for 7.5 GHz) as V → 0, which is not observed in actual practice. Since these oscillations completely disappear upon the introduction of a microwave field (curve 9), the formation of a chain of successive phase slip centers (PSC) under the action of a transport current observed by us in point contacts based on perfect YBaSrCuO single crystals [4] cannot serve on its own as the reason behind the oscillatory effects.…”