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1.
The magnetoresistance of ceramic YBa2Cu3O~6.5 HTSC samples is studied as a function of the mutual orientation of the current I and external magnetic field H ext at T = 77.3 K in magnetic fields of up to ~500 Oe. It is found that, if the demagnetization factor D is taken into account, the effective critical field of complete penetration of Josephson vortices into weak links H c2J eff does not depend on the mutual orientation of I and H ext. The lower critical field H c1A eff associated with the beginning of penetration of Abrikosov vortices into superconducting grains increases substantially with the angle between I and H ext. The strongest variation with the mutual orientation of I and H ext is exhibited by the critical field of the Bragg glass-vortex glass first-order phase transition H BG-VG eff and by the magnetoresistance jump at this phase transition. 相似文献
2.
This study aims at establishing the interrelation between the current-carrying capacity and peculiarities of magnetoresistance of granular YBa2Cu3O7 ? δ HTSCs (T c = 92.5 K). The transverse magnetoresistance of several batches of YBa2Cu3O7 ? δ HTSC samples with noticeably different values of critical supercurrent density j c is measured in magnetic fields H ext up to H ext max ≈ 500 Oe in a wide range of transport currents (5 mA ≤ I ≤ 1600 mA) at T = 77.4 K. Samples with relatively high values of j c (H ext = 0) ≥ 100 A/cm2 do not exhibit any anomalies in their field dependences. Magnetoresistance jumps δρBG-VG/ρ273K are observed for samples with low values of j c ≥ 20 A/cm2 in fields H BG-VG ≈ 200–260 Oe. The width ΔH BG-VG of the anomalous resistance region increases upon an increase in I. The magnetoresistance jumps decrease with increasing I in increasing field H ext(0 → H ext max ) and increase in decreasing field H ext(H ext max → 0). It is found that these peculiarities of the field dependences of magnetoresistance are associated with a first-order phase transition (in magnetic field) in the vortex structure of YBa2Cu3O7 ? δ HTSCs of the Bragg glass-vortex glass type. 相似文献
3.
The current-voltage characteristics of granular YBa2Cu3O6.95 high-temperature superconductor samples have been measured at a temperature of 77.3 K in external transverse magnetic fields
H
ext with a strength of up to H
ext ≈ 500 Oe for low transport current densities (0.1 A/cm2 ≤ j ≤ 0.6 A/cm2). The current-voltage characteristics obtained have been used to construct dependences of the magnetoresistance ρ on the
quantities j (ρ(j)
Hext=const) and H
ext(ρ(H
ext)
j = const). It has been revealed that the current and field dependences of the magnetoresistance exhibit anomalies at H
ext ≥ H
c1g
, where H
c1g
is the lower critical field of superconducting grains. A comparative analysis of the dependences ρ(j)H
ext = const and ρ(H
ext)
j = const has made it possible to develop concepts regarding the influence of the processes of redistribution of the magnetic field
between grain boundaries and superconducting grains on the transport and galvanomagnetic properties of granular high-temperature
superconductors. It has been established that the field dependences of the magnetoresistance exhibit specific features associated
with the beginning of penetration of Josephson vortices into grain boundaries in the magnetic field H
c1J
and with the breaking of a continuous chain of Josephson junctions in the magnetic field H
c2J
. 相似文献
4.
The character of the evolution of a system of weak links in granular high-temperature superconductors under the action of
an external magnetic field H
ext has been studied by measuring the current-voltage characteristics E(j)Hext = constE{(j)_{{H_{ext}} = const}} of YBa2Cu3O7 − δ (δ ≈ 0.05) ceramic samples. The measurements have been performed at T = 77.3 K in a range of very weak magnetic fields 0 < H
ext ≲ 0.5H
c2J, where H
c2J is the upper critical field of the Josephson weak links. The results have been used to construct the field dependences of
the magnetoresistance Δρ(H
ext) of the superconducting ceramics. It has been established that the parameters of the power equation E = A(j − j
cJ)ν and the magnetoresistance Δρ are nonmonotonic functions of the external magnetic field. The presence of extrema in the curves
A(H
ext), j
cJ(H
ext), ν(H
ext), and Δρ(H
ext) indicates that different systems of weak links between grain boundaries, which are capable of forming extended Josephson
contacts, undergo sequential transitions to a resistive state with an increase in H
ext. 相似文献
5.
The penetration of a magnetic field into superconducting grains and weak links of YBa2Cu3O7?δ ceramic high-temperature superconductors is investigated using measurements of the transverse and longitudinal magnetoresistances at T=77.3 K and 0≤H≤~500 Oe as a function of the transport current in the range ~0.01≤I/I c ≤~0.99. The effects associated with the complete penetration of Josephson vortices into weak links of the high-temperature superconductor in magnetic fields Hc2J, the onset of penetration of Abrikosov vortices into superconducting grains in magnetic fields Hc1A, and the first-order transition from the Bragg glass phase to the vortex glass phase in fields HBG-VG are revealed and interpreted. The I-H phase diagrams YBa2Cu3O7?δ high-temperature superconductors are constructed for I ⊥ H and I ‖ H. 相似文献
6.
L. Kh. Antonova A. V. Troitskii G. N. Mikhailova T. E. Demikhov S. V. Samoilenkov A. A. Molodyk J. Noudem P. Bernstein 《Bulletin of the Lebedev Physics Institute》2017,44(3):61-65
The current-carrying capability of the second-generation HTSC tapes based on GdBa2Cu3O7?x (GdBCO), produced by the SuperOx Company by the pulsed laser deposition method is studied. Critical currents inmagnetic fields aremeasured by resistive andmagnetic (using a SQUID magnetometer) methods. The results obtained are compared with characteristics of an YBCO tape grown by chemical deposition (SuperPower, USA). 相似文献
7.
Magnetic flux trapping (MFT) in granular YBa2Cu3O7 − δ high-temperature superconductors (HTSCs) is studied. At T = 77.36 K, the dependence of the hysteresis of the transverse magnetoresistance on transport current I and the maximum value of external magnetic field H
ext is found in the measurement cycle 0 → H
extmax → 0. The dependences of the parameters characterizing MFT, namely, residual magnetoresistance, field H
min at which the magnetoresistance is minimal, and the magnetoresistance at H
ext = H
min, on I and H
extmaxare determined. MFT is found to occur in HTSC granules under the action of an external magnetic field exceeding the lower
critical field of superconducting granules H
c1A, and the transport current only weakly affects the magnitude of MFT. 相似文献
8.
I. F. Voloshin A. V. Kalinov L. M. Fisher V. A. Yampol’skii 《Journal of Experimental and Theoretical Physics》2009,108(3):411-416
The dependence of the magnetization relaxation rate S = ?d lnM/dlnt on temperature T is measured in YBa2Cu3O7 ? δ samples with various oxygen concentrations. It is found that the S(T) curve changes qualitatively when oxygen deficit δ exceeds the threshold value δth = 0.37. For δ < δth (T c > 60 K, where T c is the superconducting transition temperature), function S(T) has the well-known peak at T/T c = 0.4. For δ > δth (at T c < 51 K), this peak transforms into a plateau and a new sharp peak appears at T/T c = 0.1. The threshold value δth of the oxygen deficit corresponds to the transition of the sample from the disordered state into the ordered state of oxygen vacancies. We consider the change in the shape of the S(T) curve as a macroscopic manifestation of this transition. 相似文献
9.
A. I. Golovashkin N. D. Kuzmichev V. V. Slavkin E. A. Tishchenko 《Bulletin of the Lebedev Physics Institute》2008,35(3):76-82
The temperature dependences of magnetization higher harmonics were studied experimentally in single-domain YBa2Cu3O7?x samples above T c . YBa2Cu3O7?x magnetization nonlinearity was found in different samples up to temperatures T = 103–112 K, which is much higher than the temperature of transition into the superconducting state of the given compound. The observed specific feature of YBa2Cu3O7?x magnetization is associated with the occurrence of pseudogap state in this compound. 相似文献
10.
A. V. Galeeva A. E. Parafin D. V. Masterov S. A. Pavlov A. L. Pankratov S. N. Danilov L. I. Ryabova D. R. Khokhlov 《JETP Letters》2018,107(12):785-788
Positive terahertz photoconductivity has been observed in underdoped high-temperature superconductors YBa2Cu3O7–δ at temperatures somewhat higher than the midpoint of the superconducting transition. The amplitude of the effect is almost independent of the temperature and the power of the incident radiation if the latter exceeds a certain threshold value. The mechanisms responsible for the appearance of the effect are discussed. 相似文献
11.
S.?Yu.?Gavrilkin O.?M.?Ivanenko V.?P.?Martovitski? K.?V.?Mitsen A.?Yu.?Tsvetkov 《Journal of Experimental and Theoretical Physics》2010,110(5):783-787
The temperature dependence of the heat capacity of the HTSC YBa2Cu3O6 + δ is measured in the temperature range 1.8–300 K and the doping range 0.70 < δ < 0.86. The results obtained suggest that the
transition from the 60-K to the 90-K phase in YBa2Cu3O6 + δ has a percolation nature and that the underdoped 60-K phase represents a heterophase structure in which numerous superconducting
clusters are embedded into an insulating matrix. 相似文献
12.
L. G. Mamsurova N. G. Trusevich K. S. Pigalskiy A. A. Vishnev I. V. Mamsurov 《Bulletin of the Russian Academy of Sciences: Physics》2016,80(5):504-507
Experimental evidence for the existence of chain paramagnetic Curie-type contributions to the temperature dependence of static magnetic susceptibility χ(T) in the normal (nonsuperconducting) state is obtained for a series of pure YBa2Cu3O6 + δ high temperature superconductors with different oxygen contents (0.6 < δ ≤ 1). It is shown that the chain contribution is obvious on χ(T) curves only in the T < 150K range of temperatures, grows along with the number of oxygen vacancies in Cu1–O4 chains, and depends on the ordering of these vacancies. 相似文献
13.
N. D. Kuz’michev 《Physics of the Solid State》2001,43(11):2012-2017
The differential magnetic susceptibility χd(H) of YBa2Cu3O7?x polycrystalline samples is studied experimentally in fields H<150 Oe. The empirical χd(H) dependence is determined. The results are explained on the basis of the critical-state model of a Josephson medium with hypervortices. 相似文献
14.
Kh. R. Rostami 《Journal of Experimental and Theoretical Physics》2005,101(4):653-660
The effective demagnetization factor neff of quasi-single-crystal and granular YBa2Cu3O7?x thin disks with different values of the edge barrier height, bulk pinning, and demagnetization is measured by a Hall probe with the use of a trapped magnetic flux as a test field. As the trapped magnetic flux increases, neff reaches a maximum as a function of the external field; the qualitative behavior of this maximum is independent of the morphology of a sample. It is shown that, when the densities of intragranular and intergranular critical currents differ by about one and a half orders of magnitude, the demagnetization factor neff is mainly determined by the geometry of a sample rather than by the energy of Josephson coupling between grains. The experimental results are in agreement with the results of calculations performed within the proposed model of isolated crystallites (grains). 相似文献
15.
K. V. Mitsen O. M. Ivanenko S. Yu. Burkin 《Bulletin of the Lebedev Physics Institute》2007,34(6):168-173
The dependence of the superconducting (Meissner) phase volume V m on the YBa2Cu3O6+δ doping level was studied. It was found that V m monotonically decreases as the doping level is lowered and vanishes at the same value of δ ~ 0.3 as Tc does. It was concluded that the Tc decrease and the increase in the pseudogap formation temperature T* as the doping level is lowered are caused by a decrease in the average size of superconducting clusters. This conclusion suggests an extraordinary superconductivity mechanism in HTSC. 相似文献
16.
V. I. Nikolaichik L. A. Klinkova 《Bulletin of the Russian Academy of Sciences: Physics》2016,80(12):1418-1420
Samples of high-temperature superconducting oxide EuBa2Cu3O6 + δ (Eu-123) with total cationic composition Eu: Ba: Cu = 1: 2: 3 are investigated by means of local X-ray microanalysis and high-resolution transmission electron microscopy. The cationic nonstoichiometry of Eu-123 oxide is revealed. The particles of the studied samples are inhomogeneous in structure on the nanoscale, with two types of inhomogeneities: one with typical sizes of one to several nanometers, and one with typical sizes of 10 to 20 nm, respectively. 相似文献
17.
The nonlinear magnetic properties of YBa2Cu3O7 − x
high-temperature superconducting polycrystals are investigated. Using the results of investigations as a basis, a method
for controlling the amplitudes of generated magnetization harmonics is worked out and a controllable harmonic generator is
devised. The amplitudes of the harmonics are controlled by means of a permanent magnetic field or current. The use of YBa2Cu3O7 − x
polycrystals makes it possible to produce a spectrum with offering a large number of higher harmonics. An YBa2Cu3O7 − x
-based device has a wide dynamic range; its design is simple and reliable in a wide interval of the amplitudes of an input
signal. 相似文献
18.
Temperature dependences of the resistivity ρ(T) of samples of granular high-temperature superconductor YBa2Cu3O7 – δ are measured at various transverse external magnetic fields at 0 < H ext < 1900 Оe in the temperature range from the upper Josephson critical temperature of “weak bonds” T c2J to temperatures slightly exceeding the superconducting transition temperature T c . Based on the data obtained, the behavior of the field dependences of the critical temperatures of superconducting grains and “weak bonds,” and temperature and field dependences of the magnetic contribution to the resistivity \(\left[ {\Delta \rho \left( {T,H} \right) = \rho {{\left( T \right)}_{{H_{ext}} = const}} - \rho {{\left( T \right)}_{{H_{ext}} = 0}}} \right]\). It is shown that the behavior of the magnetic contribution to the resistivity Δρ along the line of the phase transition related to the onset of the magnetic field penetration in the form of Abrikosov vortices into the subsystem of superconducting grains T c1g (H ext) is anomalous. The concepts on the magnetic flux redistribution between both subsystems of two-level HTSC near in the vicinity of T c1g : the Josephson vortex decreases, and the Abrikosov vortex density increases. 相似文献
19.
G.?Urbanik T.?H?nke C.?Hess B.?Büchner A.?Ciszewski V.?Hinkov C. T.?Lin B.?Keimer 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(4):483-489
We performed scanning tunneling microscopy and spectroscopy on untwinned crystals of underdoped YBa2Cu3O7-
δ at δ = 0.4. A comprehensive statistical analysis of our topographic data indicates a doping dependent cleaving behavior of
this material. We find in particular that at δ = 0.4 the material primarily cleaves in multiples of one unit cell along the
c-axis with a high corrugation of the topmost layer. Our data suggest that the low temperature cleaving mainly results in
a disruption of the CuO chain layers involving a redistribution of the layer atoms onto the two cleaving planes. In a few instances, fractional
step heights (in terms of the c-axis lattice constant) are observed as well. Scanning tunneling spectroscopy reveals that
such fractional steps connect surfaces which differ significantly in their tunneling conductance. 相似文献
20.
Properties of the oxygen sublattice structure of the YBa2Cu3O7 ?x crystal are studied using the diffusion model of ion channeling. The angular dependence of the elastic resonance scattering of helium ions on oxygen nuclei along the 〈001〉 direction is measured at an ion energy of 3.055 MeV. Steps are observed in the scattering yield at an angle of about 0.4°. The best fit of the calculated angular dependence of elastic resonance scattering to the experimental data is attained under the assumption that the oxygen rows contain vacancies corresponding to a fraction (not exceeding 20%) of the disordered oxygen atoms, which are randomly distributed in the plane normal to the 〈001〉 direction, and that the oxygen atoms in the rows are displaced from their equilibrium positions in a direction normal to the 〈001〉 axis. 相似文献