Dissipative conductivity of a dirty superconductor with Dynes subgap states under a dc bias current up to the depairing current density

Takayuki Kubo

doi:10.1103/PhysRevResearch.2.013302

paper

Dissipative conductivity of a dirty superconductor with Dynes subgap states under a dc bias current up to the depairing current density

arXiv:1912.01822 · doi:10.1103/PhysRevResearch.2.013302

Abstract

We study the dissipative conductivity $σ_{1}$ of a dirty superconductor with a finite Dynes parameter $Γ$ under a dc-biased weak time-dependent field. The Usadel equation for the current-carrying state is solved to calculate the pair potential, penetration depth, supercurrent density, and quasiparticle spectrum. It is shown that, while the depairing current density $j_{d}$ for $Γ = 0$ is coincident with the Kupriyanov-Lukichev theory, a finite $Γ$ decreases the superfluid density, resulting in a reduction of $j_{d}$ . The broadening of the peaks of the quasiparticle density of states induced by a combination of a finite $Γ$ and a dc bias can reduce $σ_{1}$ below that for the ideal dirty BCS superconductor with $Γ = 0$ , while subgap states at Fermi level proportional to $Γ$ results in a residual conductivity at $T \to 0$ . We find the optimum combination of $Γ$ and the dc bias to minimize $σ_{1}$ by scanning all $Γ$ and all currents up to $j_{d}$ . By using the results, it is possible to improve $j_{d}$ and reduce electromagnetic dissipation in various superconducting quantum devices.

arXiv comment9 pages, 8 figures

Dissipative conductivity of a dirty superconductor with Dynes subgap states under a dc bias current up to the depairing current density

Abstract

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