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TT: Fachverband Tiefe Temperaturen

TT 3: Superconductivity: Properties and Electronic Structure I

TT 3.4: Talk

Monday, March 12, 2018, 10:15–10:30, H 0110

Superfluid stiffness vs. electric resistance in the vicinity of the Berezinskii-Kosterlitz-Thouless transition in ultrathin aluminum films — •Lorenz Fuchs, Klaus Kronfeldner, Imke Gronwald, Dieter Schuh, Dominique Bougeard, and Christoph Strunk — Institute for Experimental and Applied Physics, University of Regensburg, 93040 Regensburg, Germany

We present superconducting properties of ultrathin aluminum films with thicknesses below 8 nm. Transport measurements are carried out in a low-noise DC configuration with IV curves spanning a voltage range of 6 orders of magnitude. Resistances are extracted from the linear parts of the curves in the zero-bias limit. Discontinuous jumps by a factor of up to 10⁵ are observed above a critical current I_c(T) at low temperature T. For moderate voltages we find a power-law dependence V∝ I^α(T) = I^{1+π J_s(T)/T}. Superfluid stiffness J_s(T) ∝ 1/λ², which is directly related to the magnetic penetration depth λ, is measured by a two-coil mutual inductance setup. We see clear signatures of a Berezinskii-Kosterlitz-Thouless transition in the low-resistance tail of the transition curve. Critical temperatures agree within a few mK for the different methods. α(T) extracted from IV curves and independently calculated from J_s(T) are compared.