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1.
I. N. Khlyustikov 《Journal of Experimental and Theoretical Physics》1997,85(3):609-615
Supercooling in the transition of a type I superconductor to the superconducting state in contact with another superconductor
whose critical temperature is higher has been measured. Using aluminum as a test material, it has been demonstrated that at
temperatures below the critical temperature T
c and magnetic fields below the critical field H
c(T), aluminum remains in a metastable normal state, in spite of its contact with another superconductor. This means that it
is not possible to generate a thermodynamic instability in a superconductor’s electronic system through the “proximity effect”
with another superconductor whose critical temperature is higher. This experimental observation demonstrates a radical difference
between surface superconductivity, which certainly generates instability in normal electronic states, and superconductivity
induced by the proximity effect near a junction with another superconductor.
Zh. éksp. Teor. Fiz. 112, 1119–1131 (September 1997) 相似文献
2.
K. Yu. Terent’ev D. M. Gokhfel’d S. I. Popkov K. A. Shaikhutdinov M. I. Petrov 《Physics of the Solid State》2011,53(12):2409-2414
The current-voltage characteristics of a porous superconductor Bi2Sr2Ca2Cu3O
x
(Bi2223) have been measured at temperatures in the range from 10 to 90 K in magnetic fields of 0–80 kOe. The experimental
dependences have been analyzed within the model allowing for pinning by clusters of a normal phase with fractal boundaries,
as well as the model taking into account phase transformations of vortex matter. It has been found that the electrical resistance
of the superconductor material significantly increases at temperatures of 60–70 K over the entire range of magnetic fields
under consideration without changing in the sign of the curvature of the dependence R(I). It has been assumed that this behavior is associated with the specific feature of the pinning in a highly porous high-temperature
superconductor, which lies in the fractality of the distribution of pinning centers in a wide range of self-similarity scales.
The studied material at the aforementioned temperatures is characterized by the melting of the vortex structure. 相似文献
3.
The electrophysical properties and structure of the nonstoichiometric high-temperature superconductor YBa2Cu3O
y
restored at T = 930–950°C after low-temperature decomposition (T = 200°C) into phases different in the oxygen content have been studied. It has been shown that, unlike heat treatments at
T ≤ 900°C, the superconducting properties are almost completely restored for 3–5 h during grain recrystallization, which is
impossible at lower temperatures. After short-term annealing at T = 930–950°C (for 1–2 h), the ceramic material still contains a significant number of structural defects, most likely, in
cation sublattices. These defects can contribute to the pinning of magnetic vortices, which substantially increases the critical
current density in magnetic fields up to 2 T as compared to ceramic materials produced by the conventional technology. 相似文献
4.
I. B. Krynetsky A. I. Golovashkin A. P. Rusakov V. P. Martovitsky S. Yu. Gavrilkin V. I. Kovalenko N. P. Shabanova 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(8):1115-1117
Abnormal negative thermal expansion of single crystals of high-temperature Bi2Sr2 − x
La
x
CuO6 + · superconductor in the dielectric phase (x ≥ 0.8) was detected at low temperatures. It was established that material shrinkage upon heating occurs at higher temperatures
than in superconducting compositions. The anisotropic and nonmonotonous effect of a magnetic field of 3–6 T on the coefficient
of thermal expansion was revealed. We attribute these abnormalities to the existence of superstructure charge ordering in
the oxygen sublattice. 相似文献
5.
Pure and Gd-doped BiFeO3 nanoparticles have been synthesized by sol–gel method. The significant effects of size and Gd-doping on structural, electrical,
and magnetic properties have been investigated. X-ray diffraction study reveals that the pure BiFeO3 nanoparticles possess rhombohedral structure, but with 10% Gd-doping complete structural transformation from rhombohedral
to orthorhombic has been observed. The particle size of pure and Gd-doped BiFeO3 nanoparticles, calculated using Transmission electron microscopy, has been found to be in the range 25–15 nm. Pure and Gd-doped
BiFeO3 nanoparticles show ferromagnetic character, and the magnetization increases with decrease in particle size and increase in
doping concentration. Scanning electron microscopy study reveals that grain size decreases with increase in Gd concentration.
Well-saturated polarization versus electric field loop is observed for the doped samples. Leakage current density decreases
by four orders by doping Gd in BiFeO3. The incorporation of Gd in BiFeO3 enhances spin as well as electric polarization at room temperature. The possible origin of enhancement in these properties
has been explained on the basis of dopant and its concentration, phase purity, small particle, and grain size. 相似文献
6.
M. N. Khlopkin G. Kh. Panova N. A. Chernoplekov A. A. Shikov A. V. Suetin 《Journal of Experimental and Theoretical Physics》1997,85(4):755-759
The specific heat and resistive upper critical magnetic field of the single crystal La1.85Sr0.15CuO4 are investigated in the temperature range 2–50 K in magnetic fields up to 8 T for two directions of the magnetic field, parallel
and normal to the ab crystalline plane. For both orientations a nonlinear (close to square root) magnetic field dependence of the mixed-state
specific heat and a positive curvature of the temperature dependence of the upper critical magnetic field are observed. Neither
of these anomalies is described by standard theories of superconductivity. Within the framework of the thermodynamic relations
it is shown that in a type-II superconductor a relationship exists between the temperature dependence of the critical magnetic
field and the field dependence of the specific heat. The anomalies observed in these phenomena are interrelated.
Zh. éksp. Teor. Fiz. 112, 1386–1395 (October 1997) 相似文献
7.
Heinz Graafsma 《Synchrotron Radiation News》2013,26(3):15-16
Copper-oxide (cuprate) high-temperature superconductors are doped Mott insulators. The undoped parent compounds are antiferromagnetic insulators, and superconductivity occurs only when an appropriate number of charge carriers (electrons or holes) are introduced by doping. All cuprate materials contain CuO2 planes (Figure 1a) in their crystal structure; the doped carriers are believed to go into these CuO2 planes, which are responsible for high-temperature superconductivity. High-temperature superconductors are characterized by their unusual physical properties, both in the superconducting state (below the superconducting transition temperature Tc) and in the normal state (above Tc). Since the discovery of high-temperature superconductivity in 1986 [1], these unusual physical properties and the mechanism of superconductivity have been prominent issues in condensed matter physics [2]. 相似文献
8.
V. V. Eremenko V. A. Sirenko G. Shimchak A. Nabyalek S. N. Barilo V. I. Gatal’skaya S. V. Shiryaev 《Physics of the Solid State》1998,40(7):1091-1095
Measurements of the magnetostriction of the isotropic high-temperature superconductor Ba0.66K0.34BiO3 revealed an effect of the order of 10−6 which exceeds that for conventional superconductors but is not as high as the giant magnetostriction of cuprate high-temperature
superconductors. A thermodynamic analysis of the results enables comparison with the results of numerical calculations of
effects induced by magnetic flux pinning.
Fiz. Tverd. Tela (St. Petersburg) 40, 1199–1203 (July 1998) 相似文献
9.
Nanoscale yttrium–barium–copper oxide (Y2BaCuO5, Y211) particles were synthesized using the emulsion method and the solution method. The basic water-in-oil (w/o) emulsion
system consisted of n-octane (continuous oil phase), cetyltrimethylammonium bromide (cationic surfactant), butanol (cosurfactant) and water. The
composition of the emulsion system was varied and characterized by measuring the conductivity of the solutions and droplet
size. The droplet size of emulsion was determined by using the dynamic light scattering method. The water content, cosurfactant
content, and surfactant/n-octane ratio affected the droplet size which was in the range of 3–8 nm, and hence the w/o emulsion system was referred to
as a nano-emulsion system. A model was used to verify the droplet size. The influence of salt (Y2(NO3)3) content on the droplet size was investigated and the addition of salt reduced the droplet size. The effects of reaction
time and temperature on the Y211 particle sizes were also investigated. The particles were characterized using the TEM, SEM,
and XRD. Nanoparticles produced by the nano-emulsion method were calcined at 850°C to form the Y211 phase as compared to solid
state processing temperature of 1050°C. Based on the TEM analysis, the average diameter of the Y211 particles produced using
the nano-emulsion method was in the range of 30–100 nm. The effect of adding 15% Y211 nanoparticles to the superconductor
YBCO-123 as flux pinning centers, was investigated, and the transition temperature was reduced by 3 K. 相似文献
10.
A. A. Zhukov N. A. Joukov M. G. Mikheev G. K. Perkins A. D. Caplin Yu. V. Bugoslavsky 《Journal of Experimental and Theoretical Physics》1998,87(1):152-161
A solution is obtained for the Bean critical-state model in an inclined magnetic field which leads to localization of the
irreversible magnetic moment induced by the shielding currents. An experimental investigation of YBa2Cu3Oy single crystals and epitaxial films, and also plates of classical superconductors using vector magnetometry yields results
fully consistent with the model calculations. The established geometric effects have an important influence on measurements
of the angular dependence of the critical current and its anisotropy in a high-temperature superconductor.
Zh. éksp. Teor. Fiz. 114, 273–290 (July 1998) 相似文献
11.
A microscopic theory of interplay of superconductivity and antiferromagnetism in rare earth ternary systems is developed from
first principles for less than half filledf atomic shells. Self consistent equations for the superconducting order parameter Δ and magnetic order parameter Γ, are derived
using a Green’s function technique and equation of motion method. The theory is applied to explain the experimental results
in the antiferromagnetic superconductor SmRh4B4. The present model explains true coexistence of superconductivity and antiferromagnetism and the suppression of superconductivity
by antiferromagnetism. The behaviour of superconducting order parameter (Δ), magnetic order parameter (Γ), the specific heat,
the density of states, free energy and critical field (H
c) is also studied for the system SmRh4B4. 相似文献
12.
13.
A. M. Petrzhik G. A. Ovsyannikov A. V. Shadrin K. I. Konstantinyan A. V. Zaitsev V. V. Demidov Yu. V. Kislinskii 《Journal of Experimental and Theoretical Physics》2011,112(6):1042-1050
Hybrid herostructures comprising an YBa2Cu3O
x
(YBCO) high-temperature superconductor (HTS) layer and Nb/Au low-temperature superconductor (LTS) bilayer (with critical
HTS and LTS temperatures T
c and T′c, respectively), separated by a thin (d
M = 5–20 nm) interlayer of LaMnO3, La0.7Ca0.3MnO3, or La0.7Sr0.3MnO3 manganite have been studied. The electric resistance and magnetic properties of individual (evaporated directly onto the
substrate) manganite films and related hybrid herostructures have been measured. Based on quasi-classical equations, analytical
expressions for the conductivity of herostructures at T ≤ T′c are obtained in the case of a low-transparency superconductor/manganite interface. It is established that the conductivity
of heterostructures is determined by the proximity effect (related to the penetration of a condensate wavefunction from the
Nb/Au bilayer to manganite) and depends strongly on interface transparency. At low temperatures (T ≪ T
c′), the conductivity peaks are found at voltages determined by the exchange field of the manganite interlayer. At T
c′ < T < T
c, conductivity features at nearly zero bias voltages are observed, which are related to the superconductivity of the YBCO
electrode. 相似文献
14.
Magnetic properties of superconducting yttrium barium copper oxide (YBa2Cu3O7-δ) nanoparticles (31–43 nm) prepared by a chemical route have been studied. These nanoparticles have been found to clearly
exhibit ferromagnetism at room temperature while superconducting transition is observed at lower temperatures. The low temperature
hysteresis loops show evidence suggesting the presence of a large paramagnetic contribution in addition to the superconducting
contributions from the particles. Bulk YBCO obtained by pelletizing and heating the same nanoparticles at a high temperature,
displays the usual superconducting characteristics and gives no trace of ferromagnetism down to 10 K. The superconducting
transition temperature of the nanoparticles is lower than for the bulk YBCO and there is a trend of decreasing T
c with smaller size of the particles. In contrast the ferromagnetic moment increases with decreasing particle size. The development
of ferromagnetism is attributed to the presence of surface oxygen vacancies that lead to electron redistribution on the different
ions at the surface. The simultaneous decrease of superconducting T
c and the increase of ferromagnetism with decreasing size considered as being reflective of the increased role of finite size
and surface defects that weaken the superconductivity and enhance the ferromagnetism. Possible coexistence of surface ferromagnetism
and bulk superconductivity at lower temperatures is discussed. 相似文献
15.
The field dependences of the transverse resistance of a single crystal of the layered superconductor Bi2Sr2CaCu2Oy (BSCCO-2212) with T
c
0≃92 K are studied in magnetic fields up to 50 T in the perpendicular orientation H⊥(ab). It is established that in the resistive region the resistance is a power-law function of the field, and the temperature
dependence of the barrier height for flux creep is obtained. It is found that in a wide temperature range, 50–125 K, the transverse
magnetoresistance of the crystal in the normal state and under conditions of superconductivity suppression by a strong magnetic
field is negative and can be approximated by a linear law with a temperature-dependent slope.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 5, 420–425 (10 September 1998) 相似文献
16.
A. G. Lebed 《JETP Letters》2012,94(9):689-692
We theoretically determine the Ginzburg-Landau slopes of the anisotropic upper critical magnetic field in a quasi-one-dimensional
superconductor and correct the previous works on this issue. By using the experimentally measured values of the Ginzburg-Landau
slopes in the superconductor (TMTSF)ClO4, we determine band parameters of its electron spectrum. Our main result is that the so-called quantum dimensional crossover
has to happen in this material in magnetic fields, H = 3–8 T, which are much lower than the previously assumed. We discuss how this fact influences metallic and superconducting
properties of the (TMTSF)2ClO4. 相似文献
17.
A.V. Eremin E.V. Gurentsov M. Hofmann B.F. Kock C. Schulz 《Applied physics. B, Lasers and optics》2006,83(3):449-454
Time-resolved laser-induced incandescence (TR-LII) was applied for the determination of particle sizes during carbon-particle formation from supersaturated atomic carbon vapor that was generated by laser photolysis of carbon suboxide (C3O2) at room temperature. Thus, the solid carbon particles were formed under hydrogen-free conditions. The TR-LII technique was used for in situ size measurement of growing carbon particles and samples of final particles were analyzed by transmission electron microscopy (TEM). It was found that the particles grow to a final size of 4–12 nm within 0.02–1 ms. The properties of the obtained particles depend on the initial conditions in the reaction volume, i.e. concentration of carbon suboxide, pressure and type of gas diluter, photolysis wavelength, and laser pulse energy. The comparison of TR-LII and TEM particle sizing results yields information about the effective thermal energy accommodation coefficients for He, Ar, CO, and C3O2 molecules on carbon particles. PACS 61.46.Df; 07.60.-j; 78.70.-g 相似文献
18.
Mn0.5Zn0.5Fe2O4 ferrite nanoparticles with tunable Curie temperature and saturation magnetization are synthesized using hydrothermal co-precipitation method. Particle size is controlled in the range of 54 to 135 Å by pH and incubation time of the reaction. All the particles exhibit super-paramagnetic behaviour at room temperature. Langevin’s theory incorporating the interparticle interaction was used to fit the virgin curve of particle magnetization. The low-temperature magnetization follows Bloch spin wave theory. Curie temperature derived from magnetic thermogravimetric analysis shows that Curie temperature increases with increasing particle size. Using these particles magnetic fluid is synthesized and magnetic characterization is reported. The monolayer coating of surfactant on particle surface is confirmed using thermogravimetric measurement. The same technique can be extended to study the magnetic phase transition. The Curie temperature derived using this measurement complies with the low-temperature magnetic measurement. The room-temperature and high-temperature magnetization measurements are also studied for magnetic fluid systems. The magnetic parameters derived for fluid are in good agreement with those obtained for the particle system. 相似文献
19.
F. V. Komissinskii G. A. Ovsyannikov N. A. Tulina V. V. Ryazanov 《Journal of Experimental and Theoretical Physics》1999,89(6):1160-1165
The electrophysical properties of heterojunctions several microns in size, obtained by successive deposition of the metal-oxide
high-temperature superconductor YBa2Cu3Ox, a normal metal Au, and the low-temperature superconductor Nb, were studied experimentally. Current flows in the [001] direction
of the epitaxial YBa2Cu3Ox film. It is shown, by comparing the experimental data with existing theoretical calculations, that for the experimentally
realizable transmittances (D̄=10−5–10−6) of the YBa2Cu3Ox—normal metal boundary the critical current of the entire heterostructure is low (of the order of the fluctuation current)
because of a sharp change in the amplitude of the potential of the superconducting carriers at this boundary. The current-voltage
characteristics of the heterostructure studied correspond to tunnel junctions consisting of a superconductor with
type symmetry of the superconducting wave function and a normal metal.
Zh. éksp. Teor. Fiz. 116, 2140–2149 (December 1999) 相似文献
20.
Coexistence of superconductivity and magnetic order has been one of the exciting aspects of the quaternary borocarbide superconductors,
So far, RNi2B2C (R=Tm, Er, Ho and Dy) are the only known magnetic superconductors in this family. Here, we present our resistivity, magnetization
and heat capacity studies on NdPt2B2C (nominal composition, NdPt1.5Au0.6B2C and NdPt2.1B2.4C1.2). We find superconductivity in both samples with T
c,onset ∼ 3 K. Bulk magnetic order is found to occur below 1.7 K. We suggest that NdPt2B2C is a possible magnetic superconductor. 相似文献