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Register a new userMagnetic Flux Periodic Response of Nano-perforated Ultrathin Superconducting Films
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Added by
James M. Valles Jr.
Publication date
2005
fields
Physics
and research's language is
English
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We have patterned a hexagonal array of nano-scale holes into a series of ultrathin, superconducting Bi/Sb films with transition temperatures 2.65 K $<T_{co} < $5 K. These regular perforations give the films a phase-sensitive periodic response to an applied magnetic field. By measuring this response in their resistive transitions, $R(T)$, we are able to distinguish regimes in which fluctuations of the amplitude, both the amplitude and phase, and the phase of the superconducting order parameter dominate the transport. The portion of $R(T)$ dominated by amplitude fluctuations is larger in lower $T_{co}$ films and thus, grows with proximity to the superconductor to insulator transition.
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Larkin and Ovchinnikov established that the viscous flow of magnetic flux quanta in current-biased superconductor films placed in a perpendicular magnetic field can lose stability due to a decrease in the vortex viscosity coefficient $eta$ with increasing velocity of the vortices $v$. The dependence of $eta$ on $v$ leads to a $nonlinear$ section in the current-voltage ($I$-$V$) curve which ends at the flux-flow instability point with a voltage jump to a highly resistive state. At the same time, in contradistinction with the nonlinear conductivity regime, instability jumps often occur in $linear$ $I$-$V$ sections. Here, for the elucidation of such jumps we develop a theory of local instability of the magnetic flux flow occurring not in the entire film but in a narrow strip across the film width in which vortices move much faster than outside it. The predictions of the developed theory are in agreement with experiments on Nb films for which the heat removal coefficients and the inelastic scattering times of quasiparticles are deduced. The presented model of local instability is also relevant for the characterization of superconducting thin films whose performance is examined for fast single-photon detection.
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