Direct evidence for filamentary and channel vortex flow in Pb/In superconducting films

Abstract

Filamentary vortex flow in thin Pb/͑14 at. %͒In films is revealed by multiple voltage jumps in currentvoltage (IV) characteristics below a critical magnetic field much lower than the upper critical field B c2 . The voltage jumps exhibit large counterclockwise hysteresis which diminishes with increasing field leading to bistable behavior close to the onset of free-flux flow. From the magnetic field and temperature dependence of the jump heights and currents at which jumps occur we infer that the number of flux lines in each channel or filament remains constant. In this regime, where the shear modulus of the vortex lattice is negligible, we find a nearly parabolic dependence of the depinning force on magnetic field, which is a signature of channel vortex motion. ͓S0163-1829͑99͒50710-8͔The vortex dynamics in type-II superconductors has received much attention partly due to its importance for the technological issue of superconductivity breakdown under a transport current, but also because its study has largely contributed to understanding disorder-driven effects on the vortex lattice. The influence of disorder potential on collective effects due to lattice pinning also plays a crucial role in related areas like Wigner-crystal formation in electron gases 1 and charge-density wave propagation. 2 In high-T c superconducting materials, phenomena such as vortex-lattice melting and the transition to a glass phase appear as a consequence of the interplay between the peculiar vortex-vortex interaction and the pinning mechanism. 3-7 Investigations of the effect of pinning on the vortex lattice as well as on vortex motion [8][9][10][11] have shown that the flux-flow behavior can be divided into two distinct regimes: elastic flow, where disorder is weak and the vortex structure essentially moves as a whole, and plastic flow with strong disorder, where the vortex lattice can be torn. The onset of vortex motion in the two regimes can differ substantially in that for plastic flow, vortices can flow in filaments or channels with the rest of the structure remaining pinned. 12,13 A model for vortex flow in the form of filaments and channels has been proposed recently 14-16 for interpreting experimental results of studies concerning the tearing of the vortex lattice 12 and the current induced transition from plastic to elastic vortex flow. 17 Time integration of the equation of motion as well as Monte Carlo techniques were applied to simulate filamentary flow of vortices and the resulting current-voltage (IV) characteristics. Furthermore, discontinuities in IV curves of 2H-NbSe 2 have been observed, 18 which were tentatively ascribed to vortex flow in channels. The channel flow state was found to be metastable and subject to strong history effects. Recently, Matsuda et al. 19 showed motion picture recordings of flowing vortices, where depinning processes of single-row vortex structures and subsequent filamentary and channel motion can clearly be seen.In this paper we report clear evidence for filamentary and channel-vortex flow, wh...

Resistance and current-voltage characteristics of individual superconductingNbSe2nanowires

“…[11][12][13] Since the self-field generated by the current does not exceed the lower critical field in the wire ͑or at the surface͒, we rule out the possibility of filamentary vortex flow, which may also generate steps in V-I curves. [21][22][23][24] In Fig. 2͑b͒, we plot the T dependence of the critical current I C ͑defined as the maximum supercurrent͒.…”

Enhanced Vortex Damping by Eddy Currents in Superconductor-Semiconductor Hybrids

“…at a distance of the order of the London penetration depth, an additional dissipation mechanism is introduced through magnetic coupling resulting in an increase of viscosity. An interesting issue is to what extent this would affect filamentary and channel vortex flow, for which dissipation jumps are observed in the current-voltage curves [8][9][10] . The study of vortex damping in hybrids may provide further insight into vortex-vortex interactions and pinning effects.…”

Experiments on Vortex Damping in Novel Superconductor-2D-Electron-Gas Hybrid Structures

“…2. For our samples the effective penetration depth is five to eight times D [8]. We are confronted with two limiting cases depending upon if either (i) D ( l 2 =d or (ii) D ) l 2 =d, i.e.…”

“…4. The point where the measurement of dissipation versus gate voltage was taken is marked with an arrow apparent in the I ±V curve are the signature of channel vortex flow [8]. The inset to Fig.…”