Metastability and transient effects in vortex matter near a decoupling transition

Abstract

We examine metastable and transient effects both above and below the first-order decoupling line in a 3D simulation of magnetically interacting pancake vortices. We observe pronounced transient and history effects as well as supercooling and superheating between the 3D coupled, ordered and 2D decoupled, disordered phases. In the disordered supercooled state as a function of DC driving, reordering occurs through the formation of growing moving channels of the ordered phase. No channels form in the superheated region; instead the ordered state is homogeneously destroyed. When a sequence of current pulses is applied we observe memory effects. We find a ramp rate dependence of the V (I) curves on both sides of the decoupling transition. The critical current that we obtain depends on how the system is prepared.PACS numbers: 74.60Ge, 74.60JgVortices in superconductors represent an ideal system in which to study the effect of quenched disorder on elastic media. The competition between the flux-line interactions, which order the vortex lattice, and the defects in the sample, which disorder the vortex lattice, produce a remarkable variety of collective behavior [1]. One prominent example is the peak effect in low temperature superconductors, which appears near H c2 when a transition from an ordered to a strongly pinned disordered state occurs in the vortex lattice [2][3][4][5][6][7][8]. In high temperature superconductors, particularly BSCCO samples, a striking "second peak" phenomenon is observed in which a dramatic increase in the critical current occurs for increasing fields. It has been proposed that this is an order-disorder or 3D to 2D transition. [9][10][11][12][13] Recently there has been renewed interest in transient effects, which have been observed in voltage response versus time curves in low temperature superconductors [5][6][7][14][15][16][17]. In these experiments the voltage response increases or decays with time, depending on how the vortex lattice was prepared. The existence of transient states suggests that the disordered phase can be supercooled into the ordered region [21], producing an increasing voltage response, whereas the ordered phase may be superheated into the disordered region, giving a decaying response. In addition to transient effects, pronounced memory effects and hysteretic V(I) curves have been observed near the peak effect in low temperature materials [2,[4][5][6][7][16][17][18][19][20]. Memory effects are also seen in simulations [22]. Xiao et al. [7] have shown that transient behavior can lead to a strong dependence of the critical current on the current ramp rate. Recent neutron scattering experiments in conjunction with ac shaking have provided more direct evidence of supercooling and superheating near the peak effect [23]. Experiments on BSCCO have revealed that the high field disordered state can be supercooled to fields well below the second peak line [24]. Furthermore, transport experiments in BSCCO have shown metastability in the zero-field-cooled state near the second peak a...

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