Static and Dynamic Vortex Phases in YBa2Cu3O7-delta (original) (raw)
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Static and Dynamic Vortex Phases in YBa2Cu3O7-d
Phys Rev Lett, 1996
Simultaneous magnetization, resistivity, and I-V measurements on YBa 2 Cu 3 O 72d show the relationship of the thermodynamic and dynamic behavior near the vortex lattice melting line. We find a coexistence region of solid and liquid at melting, with a first order magnetization jump which is independent of the vortex velocity. Sudden jumps and time dependent hysteresis of the I-V curve in the vortex solid phase are interpreted as a relaxation-pinning effect. [S0031-9007(96)01110-6] PACS numbers: 74.60. Ge, 74.25.Bt, 74.72.Bk The vortex system in high temperature superconductors is characterized by a vortex liquid phase that covers a large area in the field-temperature plane. For clean systems the transition into the vortex solid phase has been predicted to be first order , whereas in the presence of pinning induced disorder this transition is believed to be continuous, possibly to a vortex glass or Bose glass . For high quality YBa 2 Cu 3 O 72d and Bi 2 Sr 2 CaCu 2 O 8 single crystals sharp features in the resistivity [6] and discontinuous jumps in the magnetization [7-11] indicate a first order vortex transition. For both materials it is observed that the vortex melting transition is icelike, that is, the vortex density in the liquid is higher than in the solid.
First-order vortex lattice melting and magnetization of YBa�Cu�O{sub 7-δ}
Phys Rev Lett, 1995
We present the first non-mean-field calculation of the magnetization M (T ) of YBa 2 Cu 3 O 7−δ both above and below the flux-lattice melting temperature T m (H). The results are in good agreement with experiment as a function of transverse applied field H. The effects of fluctuations in both order parameter ψ(r) and magnetic induction B are included in the Ginzburg-Landau free energy functional: ψ(r) fluctuates within the lowest Landau level in each layer, while B fluctuates uniformly according to the appropriate Boltzmann factor. The second derivative (∂ 2 M/∂T 2 ) H is predicted to be negative throughout the vortex liquid state and positive in the solid state. The discontinuities in entropy and magnetization at melting are calculated to be ∼ 0.034 k B per flux line per layer and ∼ 0.0014 emu cm −3 at a field of 50 kOe. PACS numbers: 74.60.-w, 74.40.+k, 74.25.Ha, 74.25.Dw G M F , decrease with increasing temperature. From our calculated ∆S at melting and the computed slope (dH/dT ) m of the melting curve from Fig. 1, we can estimate the magnetization jump ∆M at melting via the Clausius-Clapeyron relation ∆S/∆M = −(dH/dT ) m . Inserting the calculated values of this slope and of ∆S φ , we obtain ∆M ∼ 0.0014 emu cm −3 at H = 50 kOe, and ∆M ∼ 0.0005 emu cm −3 at H = 20 kOe. These values are consistent with the directly calculated ∆M seen in . In experiment, no finite magnetization jump has yet been observed , although transport measurements on untwinned YBa 2 Cu 3 O 7−δ crystals are widely interpreted as evidence for a
First-Order Vortex Lattice Melting and Magnetization of YBa$_2$Cu$_3$O$_{7- delta}
Eprint Arxiv Supr Con 9506002, 1995
We present the first non-mean-field calculation of the magnetization M\(T\) of YBa2Cu3O7-δ both above and below the flux-lattice melting temperature Tm\(H\), in good agreement with experiment. Fluctuations in both order parameter ψ\(r\) and magnetic induction B are included in the Ginzburg-Landau free energy. The second derivative \(∂2M/∂T2\)H is predicted to be negative throughout the vortex liquid state and positive in the solid state. The discontinuity in entropy at melting is calculated to be ~0.034kB per flux line per layer at 50 kOe.
Journal of Alloys and Compounds, 2009
The effect of substitution of rare-earth Lu on the glass transition temperature (T g), the temperature and magnetic field dependent activation energy [U 0 (B,T)] and flux pinning properties of Bi 1.6 Pb 0.5 Sr 2−x Lu x Ca 1.1 Cu 2.1 O 8+ı superconductor was studied. A large broadening of resistive transition in magnetic field is observed which is a direct evidence for the thermal fluctuation in the vortex system and hence the modified vortex-glass to liquid transition theory is used to calculate the values of T g and U 0 (B,T). The resistivity shows a glassy behavior even at higher temperatures and magnetic fields for the Lu stoichiometry x = 0.100 which is believed to come mainly from the point defects arised due to the substitution of Lu atoms in the (Bi, Pb)-2212 system. The results also show that the values of T g , magnetic field dependent activation energy U 0 (B) and U 0 (B,T) are maximum for x = 0.100, which shows that the flux lines are effectively pinned and the vortices are in glassy state for this sample. The enhancement in U 0 (B,T) and the flux pinning properties of the (Bi, Pb)-2212 system due to Lu doping has both scientific and technological importance. Also, for temperatures below the superconducting transition temperature (T C), a scaling of all measured resistivity curves in magnetic field (B = 0.4 and 0.8 T) is obtained for each stoichiometry. This scaling obtained in the presence of magnetic field is quite useful for better understanding of the behavior of the vortex-liquid in high temperature superconductors.
Transport critical current and magnetization measurements of melt-processed YBa2Cu3O7−x
Journal of Applied Physics, 1988
Sheng, Z. Z.; Kiehl, W.; Marsh, D.; Elali, A.; Hambourger, Paul D.; Almasan, C.; Estrada, J.; and Datta, T., "Transport Critical Current and Magnetization Measurements of Melt-Processed YBa2Cu3O7-X" (1988). Physics Faculty Publications. Paper 94.
Physical Review B, 1993
The critical fluctuations and pinning effects in the vortex state of twinned superconducting Y-Ba-Cu-O single crystals are investigated. A second-order vortex-solid melting transition is manifested by the uniUersal static and dynamic exponents v= 3 and z =3 and the universal vortex-transport functions, independent of the experimental techniques and the magnitude and orientation of the applied magnetic fields. The vortex-correlation length and the critical-relaxation rate are also determined. The large thermal and disorder fluctuations in the vortex state of high-temperature superconductors (HTS) result in interesting vortex properties which have stimulated intense research effort. ' ' However, it is sti11 controversial whether the "phase boundary" below the meanfield upper critical field in the vortex phase diagram is a vortex-solid "melting transition, "' or an "irreversible line" that defines the onset of vortex "depinning. " Although a first-order vortex-solid melting transition may exist in untwinned, clean-limit single crystals, a secondorder melting transition should be common in most samples with moderate disorder. Such a second-order phase transition, if it exists, should be manifested by universal static and dynamic critical exponents which are indepen; dent of the sample, experimental technique, magnitude, and orientation of the applied magnetic field. However,
Physica C-superconductivity and Its Applications, 2002
We applied OFC-magnetometer (open-flat coil-based tunnel diode oscillator) to study fine peculiarities of vortex flow and magnetic phase (MP) transitions between different phases of the vortex-matter in a high quality YBa 2 Cu 3 O y crystal. The method is based on a detection of the inductance and Q-factor value changes of a single-layer flat coil, which is placed at a face of flat sample. These finally lead to frequency and/or amplitude changes of the oscillator. Simultaneous frequency and amplitude tests enabled to construct the vortex MP-diagram for untwinned YBa 2 Cu 3 O y crystal with (0:25 Â 0:6) mm 2 area and $50 lm-thick in the temperature range of 65 K to T c and the field of 0-12 T. In outlines, the plotted diagram is similar to the one defined by several other methods such as SQUID and cantilever magnetometers, etc. for the same crystal. However, our technique revealed clear separation of the lines on a diagram below the upper critical point H ucp i.e., no kink point was observed in our method. The amplitude tests revealed also some new lines on a diagram below the lower critical point H lcp (close to T c ). The obtained results may help us to understand the behavior of the vortex-mater and its dynamics in HTS materials. The problem how to improve resolution of the method for very small-size HTS objects is also discussed.
Field-cooled magnetization of YBa 2Cu 3O 7− δ superconductors
Physica C-superconductivity and Its Applications, 2000
DC susceptibility as a function of temperature was measured in both ®eld-cooled cooling and warming modes in magnetic ®elds in the range of 10 mT 6 l 0 H a 6 7 T on a variety of YBa 2 Cu 3 O 7Àd samples, comprising dierent single crystals, melt-processed bulks and polycrystalline samples, with and without KClO 3 addition. The Meissner curves measured at a ®eld of 1 mT reveal that all the samples are of a single phase. However, with increasing applied ®elds, the superconducting transitions of the single crystals and the melt-processed samples develop kinks, and above 4 T, even a secondary transition can be observed. At low temperatures, the ®eld-cooled moment increases in all samples, except the KClO 3 -doped samples, where a clear decrease is observed. These features are discussed in detail. Further, we discuss the correlation between the kinks in the DC susceptibility and the appearance of the ®shtail shape of magnetization hysteresis loops. Ó
Anisotropy of magnetization discontinuity at vortex-lattice melting in untwinnedYBa2Cu3O7−δ
Physical Review B
We measured the magnetic torque experienced by an untwinned YBa 2 Cu 3 O 7Ϫ␦ single crystal in external magnetic fields up to 0 Hϭ7 T below the critical temperature T c ϭ93.3 K, as a function of ⌰, the angle between H and the c axis of the crystal. At the vortex-lattice melting transition we observe discontinuities in both and )Hץ/ץ( T , that are related to changes in the transverse components of the magnetization vector M and (ץM/ץH) T , respectively. We use thermodynamic relationships to determine the direction of the vector ⌬M in space, and show that ⌬M is always directed parallel to M. The discontinuities in magnetization ⌬M and in entropy ⌬S vanish slightly below the temperature where the melting field H m (T) extrapolates to zero, which could indicate the existence of a lower critical point of the vortex-lattice melting line. From our )Hץ/ץ( T data we are able to extract the differences in the reduced specific heat ⌬C/T between the vortexfluid and the vortex-solid phases, and we compare these results with corresponding thermal data. We finally examine the validity of standard angular scaling rules for anisotropic superconductors for the melting fields H m (T,⌰) at temperatures as high as T/T c ϭ0.99.
Specific heat peaks observed up to 16 T on the melting line of the vortex lattice in YBa2Cu3O7
Physica C: Superconductivity, 1997
Adiabatic specific heat experiments on YBa2Cu3OT.0O are performed in magnetic fields from 0 to 16 T (Bllc and B _t_ c). The twinned, 99.995% pure 18 mg crystal is grown in an inert BaZrO 3 crucible, and oxidized in high oxygen pressure to suppress the magnetic "fishtail" effect. First-order-like specific heat peaks rising up to 1.1% above the background are observed on the melting line of the vortex lattice from 6 to 16 T (nllc). The entropy under these peaks is 0.6_ 0.1 kB/vortex/layer. The fields B m and peak temperatures T m obey the relation B m = Bo(1-Tm//Tc)4/3 with B o = 133 T. The order of the transition is investigated. Only faint anomalies are observed for Bllab. Thermodynamically incompatible specific heat steps and magnetization jumps are observed below 6 T (BIIc), suggesting irreversible glassy behaviour. No such features are seen in an YBa2Cu306.92 crystal that is characterized by strong pinning.