Dinko Babić

Reversal of Nonlocal Vortex Motion in the Regime of Strong Nonequilibrium

We investigate nonlocal vortex motion in weakly pinning a-NbGe nanostructures, which is driven by a transport current I and remotely detected as a nonlocal voltage V{nl}. At a high I of a given polarity, V{nl} changes sign dramatically. This is followed by V{nl} becoming even in I, with the opposite sign at low and high temperatures T. These findings can be explained by a Nernst-like effect resulting from local electron overheating (low T), and a magnetization enhancement due to a nonequilibrium quasiparticle distribution that leads to a gap enhancement near the vortex core (high T).

Two-dimensional decoherence effects in superconducting sheets of single crystal Bi2Sr2CaCu28+x

Abstract We quantitatively analyze ohmic magnetoresistance of a Ba 2 Sr 2 CaCu 2 O 8+ x single crystal in the temperature range 40 K ⩽ T ⩽ 76 K and in magnetic fields up to 0.8 T, with an emphasis on the non-Arrhenius high-resistivity data. The unusual field dependence of the magnetoresistance at high resistivities is shown to follow a behaviour which is characteristic for decoherence effects in two-dimensional systems. We give semiquantitative arguments which relate the observed behaviour to the magnetic-field-induced breaking of non-dissipative quasiparticle pairs occurring in the mixed state within the isolated double CuO 2 sheets. These arguments generalize the approach to the quantum decoherence phenomena, originally developed for T > T c , to T T c .

Nonlocal versus local vortex dynamics in the transversal flux transformer effect

In this follow up to our recent letter [F. Otto et al., Phys. Rev. Lett. 104, 027005 (2010)], we present a more detailed account of the superconducting transversal flux transformer effect (TFTE) in amorphous (a-)NbGe nanostructures in the regime of strong nonequilibrium in local vortex motion. Emphasis is put on the relation between the TFTE and local vortex dynamics, as the former turns out to be a reliable tool for determining the microscopic mechanisms behind the latter. By this method, a progression from electron heating at low temperatures T to the Larkin-Ovchinnikov effect close to the transition temperature Tc is traced over a range 0.26≤T/Tc≤0.95. This is represented by a number of relevant parameters such as the vortex transport entropy related to the Nernst-type effect at low T and a nonequilibrium magnetization enhancement close to Tc. At intermediate T, the Larkin-Ovchinnikov effect is at high currents modified by electron heating, which is clearly observed only in the TFTE.

Nonlocal vortex motion in mesoscopic amorphous Nb0.7Ge0.3 structures

We study nonlocal vortex transport in mesoscopic amorphous Nb0.7Ge0.3 samples. A dc current I is passed through a wire connected via a perpendicular channel, of a length L=2�5 µm, with a pair of voltage probes where a nonlocal response Vnl[proportional]I is measured. The maximum of Rnl=Vnl/I for a given temperature occurs at an L-independent magnetic field and is proportional to 1/L. The results are interpreted in terms of the dissipative vortex motion along the channel driven by a remote current and can be understood in terms of a simple model.

Strongly nonequilibrium flux flow in the presence of perforating submicron holes

Abstract We report on the effects of perforating submicron holes on the vortex dynamics of amorphous Nb 0.7 Ge 0.3 microbridges in the strongly nonequilibrium mixed state, when vortex properties change substantially. In contrast to the weak nonequilibrium—when the presence of holes may result in either an increase (close to T c ) or a decrease (well below T c ) of the dissipation, in the strong nonequilibrium an enhanced dissipation is observed irrespectively of the bath temperature. Close to T c this enhancement is similar to that in the weak nonequilibrium, but corresponds to vortices shrunk due to the Larkin–Ovchinnikov mechanism. At low temperatures the enhancement is a consequence of a weakening of the flux pinning by the holes in a regime where electron heating dominates the superconducting properties.