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Nonequilibrium Effects in Ballistic Point Contacts Ta–Cu and 2H–NbSe2–Cu: Two-Gap Superconductivity in 2H–NbSe2

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Abstract

The heterocontacts Ta–Cu and NbSe2–Cu have been studied. For the Ta–Cu contacts, the theoretical estimation of the value of δ-functional barrier at the boundary arising due to mismatch of fermionic parameters of the contacting metals is carried out and a good agreement between the calculation and experiment is obtained. An expression for the estimation of the diameter of the heterocontact on either side of the boundary is obtained. The magnitude of the jump-like decrease in the excess current (and the superconducting gap) due to the phase transition of the superconductor region near the point contact into a spatially inhomogeneous state when the critical concentration of nonequilibrium quasiparticles is reached has been determined. Obtained dependence of the additive differential resistance on the displacement at the contact arising after the phase transition, due to the excess charge of quasiparticles and the associated reverse current (or additive voltage). In 2H–NbSe2, there is a two-zone superconductivity character with \(\sim 8\) times different energy gap values. Under the influence of current injection of nonequilibrium quasiparticles, there is a sequential phase transition of layers adjacent to the point contact, in a spatially inhomogeneous state with a suppressed gap, which is accompanied by a step change in the slope of the I–V curve with a discrete increase in differential resistance, jump-like movement of the boundary between areas with suppressed and equilibrium values of the energy gaps.

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  1. B.I. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, 47 Nauka ave., Kharkov, 61103, Ukraine

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Bobrov, N.L. Nonequilibrium Effects in Ballistic Point Contacts Ta–Cu and 2H–NbSe2–Cu: Two-Gap Superconductivity in 2H–NbSe2. J Low Temp Phys 214, 399–426 (2024). https://doi.org/10.1007/s10909-024-03052-x

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