Strengthening of Reentrant Pinning by Collective Interactions in the Peak Effect

Abstract

Since it was first observed about 40 years ago [1], the peak effect has been the subject of numerous research mainly impelled by the desire to determine its exact mechanisms. Despite these efforts, a consensus on this question has yet to be reached. Experimentally, the peak effect indicates a transition from a depinned vortex phase to a reentrant pinning phase at high magnetic field. To study the effects of intrinsic pinning on the peak effect, we consider FexNi1−xZr2 superconducting metallic glasses in which the vortex pinning force varies depending on the Fe content and in which a huge peak effect is seen as a function of magnetic field. The results are mapped out as a phase diagram in which it is readily seen that the peak effect becomes broader with decreasing pinning force. Typically, pinning can be understood by increased pinning centers, but here, we show that reentrant pinning is due to the strengthening of interactions (while decreasing pinning strength). Our results demonstrate the strengthening of the peak effect by collective effects.Vortices in type II superconductors form a correlated system of interacting particles which can be studied as a function of particle density or driving force by simply tuning the external magnetic field or driving current. While elastic vortex-vortex interactions tend to order the system, vortex-pin interactions result in disorder. An ever intriguing phenomena resulting from this competition between elastic and plastic interactions is the peak effect (PE): an anomalous peak in the critical current J c (or dip in resistance) appearing with increasing temperature or magnetic field just below the transition to the normal state in some conventional superconductors [1,2,3,4,5,6], and at lower field below B c2 in high T c superconductors [7]. In type II superconductors, vortices will depin under the action of a driving force larger than the critical force. As a result of vortex motion, a dissipative voltage proportional to E =v × B wherē v is the average vortex velocity will be induced and a non-zero resistance will be measured. In the PE, some or all (reentrant superconducting phase) the vortices are pinned again, resulting in a decrease of the resistance or an increase of the critical current. The origin of the PE is still under debate. Early, it was suggested to arise due to the softening of the elastic moduli of the vortex lattice [1] and to a decrease of correlation volume V c in the collective pinning theory of Larkin and Ovchinnikov [8]. It has also been proposed to be the signature of a disorderinduced or a thermally-induced order-disorder transition [5,9,10,11,12]. However, it has equally been said to occur naturally at the crossover between a weak to strong vortex pinning regime [13]. It could also simply appear depending on the strength and density of pinning centers, and their competing action depending on magnetic field and temperature [14,15,16]. In general, the dependence of the PE on disorder is strongly dependent on the pinning mechanism: single vortex pinning...

Flux pattern transitions in the intermediate state of a type-I superconductor driven by an ac field

“…We can, therefore, suggest that the increase in interaction between flux tubes is the origin of the stability observed in the HDFTP during the flux penetration experiments. A similar effect was also reported in the peak effect regime of type-II superconductors which is ascribed to the collective pinning due to the softening of the elastic moduli of the VL [31].…”

Dynamic ordering and instability of the vortex lattice in Nb films exhibiting moderately strong pinning

“…Very recently, it has been outlined that the origin of the PE is still under debate, indeed it has been clarified that such effect strongly depends on the pinning mechanism. [8][9][10] Moreover, since the total pinning force can also depend on the bias current, a dynamical transition, known as dynamic ordering ͑DO͒, driven by an increasing bias current may occur from the disordered plastic phase which usually shows a higher F p to an ordered one, marked by a lower F p . In presence of strong spatial pinning inhomogeneity, the disordered phase can give rise to a distribution of pinning forces leading in some cases to easy flux-flow channels or to vortex shearing.…”

Equilibrium states of pancake vortices in layered superconductors: coupling of inter-layer ordering and in-layer ordering

“…pancake vortices (disordering of inter-layer structures) [6][7][8][9]. Note that such a twisting effect may also exist in normal type-II superconductors when the external field is close to the upper critical field [10,11]. After twisting or tearing of the vortex lines, vortices are much better adjusted to the random pinning sites, which greatly enhances the effective pinning forces.…”

“…After twisting or tearing of the vortex lines, vortices are much better adjusted to the random pinning sites, which greatly enhances the effective pinning forces. The enhanced pinning has many effects including an increase of critical current causing the second peak effects (SPEs), reentrant pinning effects [10,11], etc. Note that there are many interpretations to SPEs including: elastic-to-plastic crossover [12], vortex order-disorder phase transition [13], decouple transitions [8,14,15], vortex lattice structural phase transition [16], surface barriers [17], different temperature dependence of vortex-vortex interactions and vortex-pin interactions [18], etc.…”