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1.
An experimental study is reported of the effect of an electric field E⩽120 MV/m and of temperature T on the critical current I
c and I-V characteristics of yttrium-based high-T
c superconducting ceramics. The materials studied were copper-deficient ceramics, YBa2Cu3−x
Oy (D samples), and YBa2Cu3−x
Oy/Agx ceramics [S samples with silver present in amounts equal to the copper deficiency (0⩽x⩽0.4)]. It has been established that in D samples at 77 K, the electric field increases I
c and reduces substantially R for I>I
c, whereas in S samples no field effect is observed. Measurements of the I
c(T) dependence near the critical temperature showed that they can be described for all samples by a relation of the type I
c
=const(1−T/T
c
)α, where α≈1 for the D samples, and α≈2 for the S samples. The results obtained suggest that the electric-field effect correlates with the existence in the ceramic of SIS-type weak links at grain boundaries.
Fiz. Tverd. Tela (St. Petersburg) 40, 1195–1198 (July 1998) 相似文献
2.
We report the variation of the thermal diffusivity in the high temperature superconductor YBa2Cu3O7−δ below the transition temperature measured using photo-acoustic technique α is found to increase sharply belowT
c. Qualitative explanations are given. 相似文献
3.
An EPR study of the solid solutions LaSrAl1−x
CuxO4, which are isostructural to La2CuO4, shows that microphase separation of the structure occurs already at small copper concentrations (x≈0.01). A phase enriched with Cu appears along with a phase of La2AlO4, which contains isolated CuO6 centers. It is established that the nature of the states and the deformations of the CuO6 centers is determined by internal Jahn-Teller factors. When x⩽0.1, EPR signals are detected for new dynamic centers, which are identified as CuO6 Jahn-Teller centers with a hole delocalized among the four in-plane oxygen ions (the total spin S=1). When 0.1⩽x<1, local CuO
6
−
hole centers transform into magnetic Jahn-Teller polarons, which include five or more CuO6 fragments, in the copper phase of the structure. Their transformations and the conditions for observing them are discussed.
Fiz. Tverd. Tela (St. Petersburg) 40, 622–628 (April 1998) 相似文献
4.
Measurements of the coefficient of linear thermal expansion α have been carried out for the orthorhombic and tetragonal phases
of RE1Ba2Cu3O
y
(RE=Y, Gd, Dy) compounds using a high resolution capacitance dilatometer in the temperature range 77–300 K. All the superconducting
samples exhibit a jump Δα at their respective transition temperatures,T
c. Evidences of, sample-to-sample variation in α values and dependence of Δα on the sample preparation conditions, have been
obtained. The non-superconducting samples, in general, exhibit lower values of α possibly because of lowering of oxygen content. 相似文献
5.
Y. J. Uemura L. P. Le G. M. Luke B. J. Sternlieb J. H. Brewer J. Carolan W. Hardy R. Kadono R. F. Kiefl S. R. Kreitzman T. M. Riseman C. L. Seaman J. J. Neumeier M. B. Maple G. Saito H. Yamochi H. Takagi S. Uchida J. Gopalakrishnan M. A. Subramanian A. W. Sleight Gang Xiao 《Hyperfine Interactions》1991,63(1-4):131-137
We update our muon spin relaxation studies of the magnetic field penetration depth which show the correlations betweenT
c and the relaxation rate σ αn
s/m
* (carrier density/effective mass) of hole-doped high-T
c cuprate superconductors (La2, Sr3)CuO4, YBa2Cu3O7 (Y1−xPrx)Ba2Cu3O7, and other double and triple layer systems. These studies are extended to the organic superconductor (BEDT-TTF)2Cu(NCS)2. 相似文献
6.
F. Giubileo A. Jossa F. Bobba A.I. Akimenko A.M. Cucolo 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(3):305-308
We have applied the break-junction technique to highly biepitaxial c-axis oriented YBa2Cu3O7 thin films with T
C
(ρ=0) = 91 K. Mechanically adjustable junctions with a good stability and tunneling current favored along the ab-planes have been realized. The conductance characteristics of these junctions show the presence of gap related maxima that
move towards zero bias for increasing temperatures. Considering the misorientation angle α≈ 45
°
± 5
°
of the junction, a maximum gap value at the Fermi level Δ
≈ 22 meV is inferred at T
= 13 K. The temperature dependence of the gap related structures, shows a quasilinear behavior for T
> 0.4
T
C
similar to that observed in c-axis oriented, S-I-N type YBa2Cu3O7 planar junctions.
Received 20 July 2001 相似文献
7.
V. Hinkov C.T. Lin M. Raichle B. Keimer Y. Sidis P. Bourges S. Pailhès A. Ivanov 《The European physical journal. Special topics》2010,188(1):113-129
In this paper, we first give a concise overview of recent experimental and theoretical work dealing with “electronic liquid-crystal
states” which spontaneously break different symmetries of the CuO2 layers of high-T
c cuprates, with an emphasis on evidence in the spin excitation spectrum. Then we describe the importance of using twin-free
samples to look for evidence for fourfold symmetry breaking in the spectrum and explain the preparation procedure to obtain
such samples. We present inelastic neutron scattering results for moderately underdoped YBa2Cu3O6.6(T
c = 61 K) and nearly optimally doped YBa2Cu3O6.85(T
c = 89 K). In YBa2Cu3O6.6, the dispersion topology changes when heating above T
c from an hourglass shape with constricted, commensurate resonance peak to a “Y”-shape without resonance anomaly. This change,
and the fact that the low-energy signal above T
c can be described by an incommensurate, quasi-one-dimensional distribution, indicates a competition of superconductivity with
an electronic liquid-crystal state. We then show a striking analogy between the difference signal I(5 K) − I(70 K) and the downward dispersing resonance mode in YBa2Cu3O6.85. We therefore argue that a resonance mode only emerges below T
c, irrespective of the doping level. We finally discuss the implications of our results for the different scenarios invoked
to explain the electronic liquid-crystal state in cuprates. 相似文献
8.
V. É. Gasumyants E. V. Vladimirskaya M. V. Elizarova I. B. Patrina 《Physics of the Solid State》1999,41(3):350-354
Temperature dependences of the resistivity and Seebeck coefficient of Y(Ba1−x
Lax)2Cu3Oy and YBa2Cu3−x
CoxOy samples (x=0–0.25) have been measured under maximum sample saturation with oxygen, as well as following their anneal in an oxygen-deficient
atmosphere. The T
c (x) dependences for as-prepared samples were found to pass through a maximum at x=0.05, which persists after annealing for Y(Ba1−xLax)2Cu3Oy and disappears for YBa2Cu3−x
CoxOy. A phenomenological model of the band spectrum in normal phase has been used to determine the parameters of the conduction
band and of the carrier system, and to analyze their variation with the dopant type and content, as well as with annealing.
Despite the differences observed in the T
c (x) dependence, the critical temperatures for all the sample series studied were found to correlate with the conduction-band
effective width. The mechanism of the effect of impurities on the band-structure parameters and the reasons for the different
influence of annealing on the properties of Y(Ba1−x
Lax)2Cu3Oy and YBa2Cu3−x
CoxOy are discussed.
Fiz. Tverd. Tela (St. Petersburg) 41, 389–394 (March 1997) 相似文献
9.
Experimental data are given on a prototype short-circuit current limiter utilizing a polycrystalline high-T
c superconductor of composition Y1Ba2Cu3O7−δ
. The limiter comprises a seriesconnected dc circuit element immersed in liquid nitrogen. To improve the efficiency, a polycrystalline
high-T
c superconductor having an S-shaped current-voltage characteristic is used as the current limiter.
Zh. Tekh. Fiz. 68, 129–130 (October 1998) 相似文献
10.
V. F. Gantmakher G. E. Tsydynzhapov L. P. Kozeeva A. N. Lavrov 《Journal of Experimental and Theoretical Physics》1999,88(1):148-156
A superconducting transition in the temperature dependence of the ab-plane resistivity of underdoped YBa2Cu3O6+x
crystals in the range T
c≲30 K has been investigated. Unlike the case of samples with the optimal level of doping, the transition width increased insignificantly
with magnetic field, and in the range T≲13 K it decreased with increasing magnetic field. The transition point T
c(B) was determined by analyzing the fluctuation conductivity. The curves of B
c2(T) measured in the region T/T
c≳0.1 did not show a tendency to saturation and had a positive second derivative everywhere, including the immediate neighborhood
of T
c. The only difference among the curves of B
c2(T) for different crystal states is the scales of Tand B, so they can be described in terms of a universal function, which fairly closely follows Alexandrov’s model of boson superconductivity.
Zh. éksp. Teor. Fiz. 115, 268–284 (January 1999) 相似文献
11.
T. A. Ivanova Yu. V. Yablokov N. S. Zinatullina R. M. Bayazitov 《Physics of the Solid State》1999,41(3):375-378
In studying LaSrAl1−x
NixO4 ceramics, anomalies are detected in the concentration dependences of the lattice parameter c, the electrical resistance, and the sign change of the Hall constant at x≈0.6. It is shown that the collection of observed phenomena can be interpreted as a manifestation of the Jahn-Teller nature
of low-spin Ni3+ centers.
Fiz. Tverd. Tela (St. Petersburg) 41, 418–422 (March 1999) 相似文献
12.
V. G. Grebinnik V. N. Duginov V. A. Zhukov S. Kapusta A. B. Lazarev V. G. Olshevsky V. Yu. Pomjakushin S. N. Shilov I. I. Gurevich B. F. Kirillov E. P. Krasnoperov B. A. Nikolsky A. V. Pirogov A. N. Ponomarev V. A. Suetin A. I. Morozov 《Hyperfine Interactions》1991,63(1-4):241-247
High temperature superconductors HoBa2Cu3O7−δ (T
c
≅93 K), Ho0.5Y0.5Ba2Cu3O7−δ (T
c
≅93 K) and ErBa2Cu3O7−δ (T
c
≅95 K) were investigated by the zero-field μSR-technique. The muon spin depolarisation rate connected with the fluctuation
frequency of rare-earth ion magnetic moments was measured. It was found that the samples with holmium show a fast increase
of the muon spin depolarisation rate at temperatures below 20 K, while in ErBa2Cu3O7−δ the depolarisation rate remains low in the whole temperature region studied (4.2 K-270 K). The sharp difference between the
behaviours of the muon spin depolarisation rate may be explained by the difference between the ground state of Ho3+ and Er3+ ions in the crystalline field of the lattice. 相似文献
13.
N. G. Trusevich L. G. Mamsurova A. A. Vishnev N. B. Butko 《Bulletin of the Russian Academy of Sciences: Physics》2012,76(3):312-314
The temperature dependences of normal state static magnet susceptibility χ(T) for high-temperature YBa2Cu3O7 superconductors (T
c ≤ T ≤ 400 K) measured for the same sample before and after 22 years of storage are compared. It is shown that during longime
storage of a maximally doped sample, its electronic system is more in equilibrium than it was in the initial state, while
a similar underdoped sample decomposed completely. Comparing the χ(T) curves for YBa2Cu3O7, we draw conclusions as to the nature of the Curie contribution and the fluctuation-induced contribution to the magnetic
susceptibility of the investigated sample, and the experimental procedure for determining T
c. 相似文献
14.
A theoretical framework for treating the effects of magnetic fieldH on the pairing theory of superconductivity is considered, where the field is taken in an arbitrary direction with respect
to crystal axes. This is applicable to closed, as well as open normal state Fermi surface (FS), including simple layered metals.
The orbital effects of the magnetic field are treated semiclassically while retaining the full anisotropic paramagnetic contribution.
Explicit calculations are presented in the limits |H| → |H
c2(T)|,T ∼ 0 andT →T
c(|H|), |H| ∼ 0. Effects of weak nonmagnetic impurity scattering, without vertex corrections, have also been taken into account in a
phenomenological way. The final results for the case of open FS and layered materials are found to differ considerably from
those of the closed FS. For example, an important parameter,h(T=0)=|Hc2(0)|/[-Tδ|H
c2
T|δT]T{s0} for the case of a FS open ink
z-direction with thek
z-bandwidth, 4t
3, very small compared to the Fermi energy,E
F, is close to 0.5906, compared to 0.7273 for the closed FS, in the clean limit. Analytical results are given for the magnetic
field dependence ofT
c and the temperature dependence of H
c2 for a model of layered superconductors with widely open FS. For a set of band structure parameters for YBa2Cu3O7 used elsewhere, we find reasonable values for the upper critical fieldH
c2(0), the slope (dH
c2/dT)T
c0, anisotropic coherence lengths ζi(T=0),i=x, y, z, and (dT
c/d|H|)|H| → 0. 相似文献
15.
The appearance of superconductivity and the relaxation of T
c
to the equilibrium value T
c
≈30 K in a period of five days were observed in the tetragonal ceramic NdBa2Cu3O6.67 under a pressure of 1 GPa. The superconducting phase vanishes 1.3 h after the pressure is released. This behavior is explained
by the charge redistribution occurring as a result of pressure-induced ordering of oxygen in the CuOx planes.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 10, 784–787 (25 May 1996) 相似文献
16.
The real and imaginary parts of the surface impedance Z
s
=R
s
+iX
s
of YBa2Cu3O6.95 single crystals are measured at a frequency ω/π=9.4 GHz. The quantities R
s
(T) and X
s
(T) are linear functions of temperature for T<0.3T
c
(T
c
=93.5 K). A maximum of R
s
(T) and a plateau of X
s
(T) are observed in the interval 35<T<65 K. Our experimental data, just as all recent measurements of R
s
(T) in YBa2Cu3O6.95 single crystals in the temperature range 0<T<1.3T
c
, are described well in a two-fluid model which assumes electron-phonon scattering of quasiparticles.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 12, 893–898 (25 June 1997) 相似文献
17.
A comprehensive review of structure work on high-T
c
oxides as reported during the years 1987 and 1988 is given. Thirteen structures are refined from X-ray single-crystal and/or neutron powder diffraction data:I. (Ba1–x
,K
x
)BiO3 (T
c
=30 K),II. (La2–x
, Sr
x
)CuO4 (T
c
=40 K),III. (Nd, Ce, Sr)2CuO4 (T
c
=28 K),IV. (Nd2–x
, Ce
x
)CuO4 (T
c
=24 K),V. YBa2Cu3O7 (T
c
=90 K),VI. YBa2Cu4O8 (T
c
=80 K),VII. Y2Ba4Cu7O14 (T
c
=40 K),VIII. Pb2Sr2NdCu3O8 (T
c
=70 K),IX. TlBa2CaCu2O7 (T
c
=103 K),X. TlBa2Ca2Cu3O9 (T
c
=120 K),XI. Tl2Ba2CuO6 (T
c
=90 K),XII. Tl2Ba2CaCu2O8 (T
c
=112 K),XIII. Tl2Ba2Ca2Cu3O10 (T
c
=125 K). Except forI (perovskite type),II (K2NiF4 type) andIV (Nd2CuO4 type) they represent new structure types. Structure data, bond distances, structure drawings and calculated X-ray powder diffraction patterns are given for each compound. Structural features and correlations with superconductivity are discussed. The review contains 301 citations. 相似文献
18.
A. A. Zhukov M. R. Trunin A. T. Sokolov N. N. Kolesnikov 《Journal of Experimental and Theoretical Physics》1997,85(6):1211-1217
The real part R
s and the imaginary part X
s of the surface impedance Z
s=R
s+ iX
s of Tl2Ba2CaCu2O8−δ
and YBa2Cu3O6.95 single crystals have been measured with high precision at frequency ω/2π=9.4 GHz in the temperature range 0<T<140 K. In the Tl2Ba2CaCu2O8−δ
crystal a linear temperature dependence R
s(T) has been found for T⩽50 K, and the magnetic field penetration depth λ(4.2 K)=X
s(4.2 K)/ω μ
0≈3760 Å has been measured. Along with well known features of the function Z
s(T) in high-quality YBa2Cu3O6.95 single crystals, such as the linearity of λ(T) and R
s(T) for T<T
c/3 and a maximum of R
s(T) at T∼T
c/2, the linearity range of λ(T) extends to T≃50 K, and this curve has a plateau in the range 60<T<85 K. The curve of R
s(T) in both the superconducting and normal states of YBa2Cu3O6.95 is well described by a two-fluid model with the electron-phonon mechanism of quasiparticle relaxation. A formula describing
the curve of λ
2(0)/λ
2(T) throughout the studied temperature range is also given.
Zh. éksp. Teor. Fiz. 112, 2210–2222 (December 1997) 相似文献
19.
The relaxation of the superconducting transition temperature T
c in YBa2Cu3O6.38 is investigated with increasing oxygen order in the CuOx plane under 1 GPa pressure and with decreasing oxygen order after the pressure is relieved. It is established that the oxygen
disordering process is more rapid than the pressure-induced ordering process: The ratio of the relaxation times of T
c in these processes τ
ord/τ
disord≈5. This behavior could be caused by different mechanisms of the pressure-induced increase in the Cu-O chain length and decrease
of this length after pressure relief.
Fiz. Tverd. Tela (St. Petersburg) 40, 1968–1973 (November 1998) 相似文献
20.
M. K. Aliev G. R. Alimov T. M. Muminov B. A. Olimov Kh. I. Turkmenov I. Kholbaev L. I. Leonyuk R. F. Rumi 《Physics of the Solid State》1999,41(1):11-14
Y1Ba2Cu3O7−x
single crystals are investigated near T
c
≈92 K in fields 0<H⩽9 kOe using a modified ESR spectrometer. The temperature modulation method is used for the first time, together with the
traditional magnetic modulation method, to detect microwave responses in single crystals. Superconducting-transition peaks
shifted relative to one another in temperature and differing in shape are observed in the temperature dependence of the corresponding
signals ∂R/∂H and ∂R/∂T (R — microwave absorption). The evolution of these peaks as a function of the field and the angle π between H and the c axis of the single crystal is traced. It is shown that the difference in the temperature dependences of the derivatives ∂R/∂H and ∂R/∂T is due to the broadening of the superconducting transition characteristic of HTSCs.
Fiz. Tverd. Tela (St. Petersburg) 41, 14–17 (January 1999) 相似文献