Magnetization Jumps and Irreversibility in Bi_2Sr_2CaCu_2O_8 (original) (raw)
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Different roles of anisotropy and disorder on the vortex matter of Bi2Sr2CaCu2O8+δ single crystal
Physica C: Superconductivity, 2002
The oxygen doped and Pb-substituted single crystalline Bi 2 Sr 2 CaCu 2 O 8þd samples having T c;on and anisotropy ðc 2 Þ ranging respectively from 65 to 93 K and from 773 to 49,715 have been studied in the basis of magneto-resistance and magnetization data. It is found that the lowering of anisotropy due to higher oxygen content or Pb substitution is responsible for the reduction of magnetic field-induced transitional broadening and a shift of H irr ðT Þ and H g ðT Þ to higher temperatures and magnetic field. Meanwhile, the increasing disorder manifested by decreasing T c also leads to the extended range of appearance for the second magnetization peak (SMP) and enlarged critical glassy region. It is shown that decreasing anisotropy does not necessarily lead to the lowering of T c in contrast to the monotonic dependence of T c on the disorder measured in the temperature range of SMP effect. Additionally, a remarkable monotonic correlation between T c and the glassy exponent s has been established. : S 0 9 2 1 -4 5 3 4 ( 0 2 ) 0 1 4 7 5 -2 0921-4534/02/$ -see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 -4 5 3 4 ( 0 2 ) 0 2 2 9 2 -X Physica C 385 www.elsevier.com/locate/physc
Vortex crossing lattice phase transition in single crystalline Bi2Sr2CaCu2O8+
Physica C: Superconductivity, 2004
The vortex state in highly anisotropic overdoped Bi 2 Sr 2 CaCu 2 O 8þd superconductor with T c ¼ 84:5 K has been studied by the local ac-permeability (l ¼ l 0 À il 00) measurements in magnetic fields tilted away from the c-axis to the abplane. In the present measurements, we have observed the vortex lattice melting transition, the peak effect, and several anomalies of the local ac-response in the vortex solid phase that suggest the novel phase transitions in the vortex crossing lattice state.
Composite to Tilted Vortex Lattice Transition in Bi2Sr2CaCu2O8+δ in Oblique Fields
Physical Review Letters, 2006
Precision measurements of the vortex phase diagram in single crystals of the layered superconductor Bi2Sr2CaCu2O 8+δ in oblique magnetic fields confirm the existence of a second phase transition, in addition to the usual first order vortex lattice melting line Hm(T ). The transition has a strong first order character, is accompanied by strong hysteresis, and intersects the melting line in a tricritical point (H ⊥ m , H cr ). Its field dependence and the changing character of the melting line at the tricritical point strongly suggest that the ground state for magnetic fields closely aligned with the superconducting layers is a lattice of uniformly tilted vortex lines. PACS numbers: 74.25.Qt, 74.25.Op, 74.25.Dw The first order "vortex melting" transition from a solid (phase-ordered) state to a liquid state with only short range correlations is the main feature of the phase diagram of vortex lines in clean, layered high-temperature superconductors . The application of a small field component H , parallel to the superconducting layers, leads to a lattice of tilted vortex lines that melts in a similar fashion . However, in the more anisotropic (layered) compounds such as Bi 2 Sr 2 CaCu 2 O 8+δ , the depression of the perpendicular component of the melting field H ⊥ m by larger parallel fields was interpreted as the consequence of the decomposition of the tilted vortex lattice into a combined lattice structure of Josephson Vortices (JVs) and Abrikosov-type pancake vortices (PVs) . For very small field components H ⊥ perpendicular to the layers, chain structures [3] arising from the attractive interaction of PVs with JVs were directly visualized by Bitter decoration , scanning Hall-probe [3, 6] and magnetooptical techniques . At higher H ⊥ ∼ H ⊥ m , the contribution of the JVs to the free energy of the pancake vortex crystal results in the almost linear depression of H ⊥ m as function of the parallel field . This behavior in moderate H stops at a temperature dependent characteristic field H cr . Even though melting is still observed above H cr , the variation of H ⊥ m with increasing H becomes much weaker . Several controversial interpretations of this changing behavior were proposed, such as layer decoupling [11], a commensurate transition , and a matching effect .
Snapshots of the flux distribution during magnetization reversal of a high-temperature superconductor Bi 2 Sr 2 CaCu 2 O 8+␦ single crystal in the presence of artificial columnar defects were recorded using magnetic force microscopy. Thereby, the flux-antiflux boundary width and its displacement by annihilation of individual vortex-antivortex pairs could be visualized. In general the flux density follows Bean's model. However, step dislocations with a strongly anisotropic pinning behavior lead locally to a nonmonotonous flux distribution and result in a delay of the boundary propagation.
Vortex lattice in Bi2Sr2CaCu2O8 well above the first-order phase transition boundary
Physica C: Superconductivity, 2004
Measurements of non-local in-plane resistance originating from transverse vortexvortex correlations have been performed on a Bi 2 Sr 2 CaCu 2 O 8+δ high-T c superconductor in a magnetic field up to 9 T applied along the crystal c-axis. Our results demonstrate that a rigid vortex lattice does exist over a broad portion of the magnetic field-temperature (H-T) phase diagram, well above the first-order transition boundary H F OT (T). The results also provide evidence for the vortex lattice melting and vortex liquid decoupling phase transitions, occurring above the H F OT (T).
Physical Review Letters, 2008
A low concentration of columnar defects (CDs) is reported to transform a first-order vortex lattice melting line in Bi2Sr2CaCu2O8 crystals into alternating segments of first-and second-order transitions separated by two critical points. As the density of CDs is increased, the critical points shift apart and the range of the intermediate second-order transition expands. A third, low temperature critical point was also observed in one sample. The measurement of equilibrium magnetization and the mapping of the melting line down to 27K was made possible by employment of the shaking technique.
Supercooling of the Disordered Vortex Lattice in Bi2Sr2CaCu2O8+δ
Physical Review Letters, 2000
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Manipulation of magnetic-flux landscapes in superconducting Bi2Sr2CaCu2O8+ δ crystals
2007
We demonstrate experimentally that the micromagnetic profile of the out-ofplane component of magnetic induction of layered superconductors, Bz, can be manipulated by varying the in-plane magnetic field, H . Moving Josephson vortices, confined between layers, drag pancake vortex stacks carrying out-of-plane flux, and the magnetic profile, Bz(x), can be controllably shaped across the entire sample. Depending on the magnetic history and temperature we can increase or decrease the out-of-plane flux density at the center and near the edges of the crystal by as much as ∼ 40%, realising both "convex and concave magnetic flux lenses". Our experimental results are well described by molecular dynamics simulations.
Entropy jump at the first-order vortex phase transition in Bi2Sr2CaCu2O8+δ with columnar defects
Materials Today: Proceedings, 2019
We study the entropy jump associated with the first-order vortex melting transition (FOT) in Bi 2 Sr 2 CaCu 2 O 8+δ crystals by means of Hall probe magnetometry. The samples present a diluted distribution of columnar defects (CD) introduced by irradiation with Xe ions. The FOT is detected in ac transmittivity measurements as a paramagnetic peak, the height of which is proportional to the enthalpy difference entailed by the transition. By applying the Clausius-Clapeyron relation, we quantify the evolution of the entropy jump Δs as a function of the FOT temperature, T FOT , in both pristine crystals and crystals with CD. On increasing the density of CD, Δs decreases monotonically with respect to values found in pristine samples. The Δs versus T FOT dependence in the case of pristine samples follows reasonably well the theoretical prediction of dominant electromagnetic coupling for a model neglecting the effect of disorder. The data for samples with a diluted distribution of CD are not properly described by such a theoretical model.
arXiv (Cornell University), 2019
We study the entropy jump associated with the first-order vortex melting transition (FOT) in Bi 2 Sr 2 CaCu 2 O 8+δ crystals by means of Hall probe magnetometry. The samples present a diluted distribution of columnar defects (CD) introduced by irradiation with Xe ions. The FOT is detected in ac transmittivity measurements as a paramagnetic peak, the height of which is proportional to the enthalpy difference entailed by the transition. By applying the Clausius-Clapeyron relation, we quantify the evolution of the entropy jump Δs as a function of the FOT temperature, T FOT , in both pristine crystals and crystals with CD. On increasing the density of CD, Δs decreases monotonically with respect to values found in pristine samples. The Δs versus T FOT dependence in the case of pristine samples follows reasonably well the theoretical prediction of dominant electromagnetic coupling for a model neglecting the effect of disorder. The data for samples with a diluted distribution of CD are not properly described by such a theoretical model.