M.V. Indenbom

Magnetization decay due to vortex phase boundary motion in BSCCO

Abstract We identify a new regime of decay of the irreversible magnetization in clean Bi 2 Sr 2 CaCu 2 O 8 crystals, at induction values close to the “second peak field” at which the bulk critical current density steeply increases. A time window is identified during which the decay of the induction is controlled by the slow propagation of the phase transformation front across the sample.

Melting of regular and decoupled vortex lattices in BSCCO crystals

Abstract The angular dependence of the first-order phase transition (FOT) in the vortex lattice in Bi 2 Sr 2 CaCu 2 O 8 crystals was investigated by a low frequency AC shielding technique (with the AC field ‖ c ), in which the static-field component parallel to c - ( H ⦜ ) was varied with the in-plane field H ‖ held constant. The linear decrease of the FOT field H FOT ⦜ with increasing H ‖ ends at a temperature—dependent critical value of H ‖ . A new transition, marked by the abrupt drop of the ab -plane shielding current, appears at this point. We draw a new phase diagram with H ‖ and H ⦜ field components as coordinates; this features at least two distinct regions in the vortex solid phase, that are determined by the different interplay between the pancake vortex— and Josephson vortex lattice.

Gigantic surface pinning created by columnar defects

Abstract Columnar tracks created by high energy heavy ions are considered to be the most efficient defects since they pin the vortices over their whole length. However, our magneto-optical observations and local Hall-probe measurements of the magnetization of YBa 2 Cu 3 O 7−δ single crystals with columnar defects reveal that at moderate fields the shielding current due to pinning by the columns is not proportional to the sample thickness, as it should be in the case of bulk pinning. We conclude that, in contradiction to what is commonly believed, the vortices are depinned from the columnar defects only at the surface. Experiments supporting this idea are reported and the peculiarities of this gigantic surface pinning are discussed.

Magnetic relaxation in the “Bragg-glass” phase in BSCCO

Magnetic relaxation in the Bragg-glass phase of overdoped Bi 2 Sr 2 CaCu 2 O 8 crystals was investigated using time-resolved magneto-optical visualisation of the flux distribution. This has permitted us to extract the current-voltage characteristic, which can be well described by a power-law, although fits to a stretched exponential E ∼ exp(-j c /j) μ with 0.3 < p < 0.8 are possible at long times in excess of 100 s.

Supercooling of the high field vortex phase in single crystalline BSCCO

Abstract Time resolved magneto-optical images show hysteresis associated with the transition at the so-called “second magnetization peak” at B sp in single-crystalline Bi 2 Sr 2 CaCu 2 O 8+δ . By rapid quenching of the high-field phase, it can be made to persist metastably in the sample down to fields that are nearly half B sp .

First Order Transition of the Vortex Lattice in Disordered BI-2212 Crystals

Using differential magneto-optical imaging, we address the question of meso-scopic inhomogeneity in underdoped Bi2Sr2CaCu2O8 (Bi-2212) single crystals. Among other features, it is shown that an anomalous temperature dependence of the penetration field and of the first order transition (FOT) field of the vortex lattice in such crystals can be understood as arising from inhomogeneity. The effect of chemical inhomogeneity and pinning on flux penetration and the FOT is discussed.

Spatially resolved resistivity near the vortex lattice phase transition in Bi2Sr2CaCu2O8+δ single crystals

Abstract Using a multiterminal contact configuration, we investigate the local variations of the resistivity drop near the vortex lattice first order phase transition in a very homogeneous Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO) single crystal.