Electron-electron scattering and phase fluctuations in superconducting films

Abstract

The effects of weak disorder on superconducting aluminum films are studied over temperatures 0.4Tc≤T≤0.98Tc and resistances per square of 1.7≤R□≤22 Ω. The primary effects of disorder are found to be disorder-enhanced electron-electron scattering and thermal phase, or supercurrent fluctuations, both of which cause pair-breaking effects. This conclusion is drawn from measurement of the low-voltage resistance of low-resistance superconductor–insulator–normal-metal (SIN) tunnel junctions with aluminum as the S electrode. The effective pair-breaking rates from both processes, evaluated at Tc, increases linearly with R□, in semiquantitative agreement with model calculations. The electron-electron scattering rate decreases very rapidly as T decreases below Tc, in agreement with theory. The pair-breaking rate from phase fluctuations decreases roughly linearly with decreasing temperature. Although distinct effects, phase fluctuations, and electron-electron scattering share a common origin in electron-density fluctuations, which are enhanced by disorder. A microscopic theory of disordered superconductors incorporating both electron-electron scattering and thermal phase fluctuations is needed.

Source-reported materials — not catalogue approval

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