On voltage-current characteristics and critical current in Bi-2212

Abstract

V(I) characteristics have been performed in a monocrystalline microbridge of Bi[P b] − 2212. The vortex phase diagram has been greatly investigated. Linear but non-ohmic Voltage(Current) (V(I)) curves with well defined critical current have been observed. A departure from this behavior is observed near the peak effect where an out of equilibrium high threshold current can be stabilized. At high temperature, the critical current persists in the "liquid" state despite the dissipation at the lowest bias. Some implications of these results are discussed. In particular, it is proposed that the surface disorder, rather than the bulk disorder, is responsible for the vortex pinning in this sample. The generic vortex phase diagram in cuprates is now described in terms of into different thermodynamic phases of vortex [1]. The main idea is that an ordered Vortex Lattice (VL) is present at low field and low temperature, and that it develops into a phase possessing a degraded order when the thermal fluctuations or the static disorder are increased. This corresponds respectively to (ordered solid/liquid) and (ordered solid/disordered solid) transitions. The strong experimental facts which have justified these ideas are the disappearance of the vortex pinning in the "liquid" phase and the increase of this vortex pinning (the peak effect) when crossing the disordering transition. The highly anisotropic cuprate Bi-2212 can be taken as a representative sample where these three states can appear. Nevertheless, recent experiments suggest to qualify this point of view. Indeed, it has been found that both the high field and the high temperature properties can be interpreted with the same state of vortex matter, meaning that no difference between them should be presupposed [2,3]. Another striking result is that VL translational order is not a good order parameter to characterize the first order transition [4], whereas one could have expected the contrary for a genuine melting. From an experimental point of view, the VL behavior in Bi-2212 has been tackled at low field by magneto-optic imaging or local ac probes [2,3], which are sensitive to pinning induced screening currents on the surface of the samples. If the magnetic field is increased, the limited resolution of the above-cited experiments strongly restricts their ability to give information on the VL pinning and dynamical properties. One complementary and easily understandable experiment is the measure of a voltage versus current (V(I)) curve. The critical current I c , which gives the pinning ability of the medium, can be extracted without the need of complicated and possibly unjustified assumptions. Furthermore, it has been shown by numerous theories and simulations [5,6,7] that the nature of the VL

Persistence of characteristics of an ordered flux line lattice above the second peak in $Bi_2Sr_2CaCu_2O_{8+ δ}$

“…Transport experiments suggest that these latter can be also important in Bi − 2212, and metastable transport properties, very similar properties with those observed in NbSe 2 , are also observed [26]. It is very important to note that if there is a coexistence between two states, the states observed here under the strongest magnetic fields can be metastable.…”

Persistence of an ordered flux line lattice above the second peak inBi2Sr2CaCu2O8Pautrat1, Simon2, Goupil3 et al. 2007Phys. Rev. BSelf Cite150170View full textAdd to dashboardCite

“…25 Transport experiments suggest that these latter surface currents can be also important in Bi-2212, and metastable transport properties, very similar properties with those observed in NbSe 2 , are also observed. 26 It is very important to note that if there is a coexistence between two states, the states observed here under the strongest magnetic fields can be metastable. In such a case, their relative quantities can be modified by making various magnetic or thermal histories.…”

Critical Current Density and Meissner Effect of Smart Meta-Superconductor MgB2 and Bi(Pb)SrCaCuO

“…After a certain current I is input into the sample through the current lead, the voltage V of the sample is measured. The critical current I C is defined as the transport current when a significant drift voltage exists [ 9 , 10 , 11 ]. The current–voltage ( I – V ) curve is used to determine the critical current I C , which then enables the determination of the critical current density J C [ 12 , 13 ].…”