Metastability and Glassy Behavior of a Driven Flux-Line Lattice

Abstract

Strong metastability and history dependence are observed in DC and pulsed transport studies of flux-line lattices in 2H-N bSe2, leading to the identification of two distinct states of the lattice with different spatial ordering. The metastability is most pronounced upon crossing a transition line marked by a large jump in the critical current (the peak effect). Current induced annealing of the metastable state towards the stable state is observed with a strongly current dependent annealing time, which diverges as a threshold current is approached from above.PACS numbers: 74.60.Ge 74.60.Jg 74.60Ec In the absence of disorder the physics of a magnetic flux-line lattice (FLL) is governed by the interplay between thermal fluctuations, which favor melting, and interactions, that lead to ordering. The resulting phase diagram consists of a liquid and a solid phase with relatively simple dynamics. Quenched disorder causes the system to develop additional phases and complex dynamic effects such as pinning and irreversibility in the magnetic and electric responses. The role played by disorder and pinning in the physics of FLL in equilibrium has recently become an area of intense study [1,2]. A related but distinct topic of current interest concerns the role of motion on the spatial ordering of the FLL, the resulting dynamical transitions or crossovers that may occur, and the relation they bear to the disorder free situation [3][4][5][6][7].In this Letter we report on the existence of two distinct states of the FLL, one disordered, the other much less disordered (hereafter referred to as the ordered state) , with strikingly large differences between their transport properties. As a result the system displays a wide range of phenomena such as history-dependence, metastability, current-induced annealing and glassy relaxation. Each of these states is stable in its own sharply defined region of the (H,T) plane and metastable elsewhere and each can be accessed with a simple reproducible procedure. Our experiments show directly that the metastable state can be annealed into the "equilibrium" state by applying a current that depins the FLL. The annealing kinetics is found to be strongly current dependent, with the annealing time diverging as the depinning current is approached from above. The variation of these phenomena with field, temperature, and driving current provides direct access to the interplay between static and dynamic transitions and can elucidate the role of disorder in different parts of the FLL phase diagram. Our results can also be used to interpret the rich and complex history dependence studied earlier in low T c superconducting films [8,9].The history dependence is closely associated with the phenomenon of "peak effect". This effect, which is observed in many weak-pinning superconductors, is charac-

Grain boundaries in vortex matter

“…As the magnetic induction approaches its critical value, a sudden increase in measured critical currents is observed in both the ZFC and the FC experimental setup. 42,44 …”

“…On the other hand, ordered vortex crystals can be obtained in zero-field-cooling ͑ZFC͒ experiments, i.e., applying a magnetic field only after temperature has been lowered to the expected value. 10,[41][42][43][44][45][46] The FC state is usually characterized by a higher critical current and has been proven to be metastable. 42,44 These aspects result in a peculiar hysteretic behavior commonly observed in critical current measurements 42,44 and I-V characteristics.…”

“…10,[41][42][43][44][45][46] The FC state is usually characterized by a higher critical current and has been proven to be metastable. 42,44 These aspects result in a peculiar hysteretic behavior commonly observed in critical current measurements 42,44 and I-V characteristics. 41,43 In our numerical analysis, the evaluation of critical currents in perfect vortex crystals ͑lower line in Fig.…”

“…This result can explain the difference in transport properties between field-cooled and zero-fieldcooled samples and the related hysteresis commonly measured experimentally. 10,[41][42][43][44][45][46] Finally, we discuss the possible role of grain boundary in vortex lattice melting by constructing a free-energy functional for the grain boundary density along the lines of Ref. 38.…”

Anisotropic response of the moving vortex lattice in superconducting Mo(1−x)Gex amorphous films

“…Transport measurements report changes in the dynamical properties of the vortex matter close to the peak effect [4,5,6,7] that were attributed to a crossover from plastic to ordered motion. More recently Kokubo and coworkers [8] have proven this dynamical ordering from mode locking experiments.…”