Berlin 2018 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 15: Focussed Session: Geometry- and Topology-Controlled Nanoarchitectures I

HL 15.4: Talk

Tuesday, March 13, 2018, 10:15–10:30, EW 015

Microwave-stimulated superconductivity in Nb thin films — •Oleksandr V. Dobrovolskiy^1,2, Roland Sachser¹, Michael Huth¹, Antonio Lara³, Farkhad G. Aliev³, Valerij A. Shklovskij², Alexei I. Bezuglyj^2,4, and Ruslan V. Vovk² — ¹Goethe University, Frankfurt am Main, Germany — ²V. Karazin National University, Kharkiv, Ukraine — ³Universidad Autonoma de Madrid, Spain — ⁴National Science Center – KIPT, Kharkiv, Ukraine

Stimulation of superconductivity due to the presence of vortices by a microwave (mw) excitation has been recently seen in increase of T_c and H_c2 in type II superconducting thin films. Here we report on a mw-induced enhancement of the maximal mixed-state dc critical current of epitaxial Nb films. The mw-stimulated flux flow is expanded up to 10% larger dc current densities and vortex velocities v^∗ than in the absence of mw stimulus. Here j^∗ and v^∗ correspond to an abrupt transition of the sample into the normal state because of the Larkin-Ovchinnikov (LO) instability. We have performed simulations of the time-dependent Ginzburg Landau (TDGL) equation, which reveal similar results to the ones observed in the experiments. These can be interpreted as a result of massless response of vortices to an external excitation, or as mw-stimulated superconductivity as vortices approach the critical velocity. We furthermore argue that the observed mw-induced enhancement of j^∗ and v^∗ can result in a competition between the mw-induced cooling and the dc-induced heating of quasiparticles in the vortex cores.