共查询到20条相似文献,搜索用时 15 毫秒
1.
The electronic specific heat Cel was studied in Ga- and Zn-doped La2–xSrxCuO4 (0.16x0.22) at T10K. Partial substitution of Ga or Zn for Cu suppresses Tc and revives the T-linear electronic specific heat, T, markedly. The (y)/n vs Tc/Tc0 relation for Zn-doped samples with x0.2 is in good agreement with the theoretical one for resonant impurity scattering in a d-wave superconductor, while those for Ga-doped samples and for Zn-doped samples with x 0.2 deviate slightly from the theoretical curve. The deviation will be discussed in relation to changes in the magnetic properties of 3d electrons. 相似文献
2.
Hiroyuki Fujishiro Manabu Ikebe Yuzo Shibazaki 《Journal of Low Temperature Physics》1999,117(5-6):1181-1185
The thermal conductivity has been measured for La
2-X
Sr
X
CuO
4
and La
1.85
Sr
0.15
Cu
0.98
M
0.02
O
4
(M; Zn, Ni). The characteristic enhancement in below T
c
was confirmed for La
1.85
Sr
0.15
CuO
4
. The phonon scattering mechanisms were analyzed in detail and the electron-phonon coupling constant was estimated to be 0.05. The enhancement becomes indetectable on Zn or Ni substitution for Cu, which indicated survival of the phonon scattering by charge carriers down to lower temperatures as a result of reduced T
c
. 相似文献
3.
Heon-Jung Kim C. U. Jung J. Y. Kim Min-Seok Park Mun-Seog Kim Sung-Ik Lee 《Journal of Low Temperature Physics》2003,131(3-4):625-629
We used X-ray diffraction, energy dispersive spectroscopy and low field magnetization to characterize Sr0.9La0.1Cu1–x
R
x
O2 samples for R=Zn and Ni. We found that both Ni and Zn are substituted at the Cu-site. The value of T
c was almost independent of composition until x0.03 for R=Zn while it was reduced to 30 K at x0.02 for R=Ni. This trend of T
c reduction is very similar to the pair breaking-effect in conventional superconductors and electron-doped (Nd, Ce)2CuO4– but the rate of reduction of T
c for R=Ni is larger in Sr0.9La0.1CuO2 than in (Nd, Ce)2CuO4–. These results are discussed along with the recent experimental observation of gap symmetry in electron-doped superconductors. 相似文献
4.
Temperature dependence of surface impedance Z(T, ω) and mean free paths I(T) of YBCO-superconductors
K. Numssen R. Schwab T. Jacobs R. Heidinger J. Halbritter 《Journal of Low Temperature Physics》1996,105(3-4):1041-1046
The surface impedance Z(T,) at 10 and 145 GHz and between 4 and 300 K is obtained experimentally. Z(TaTTc) is quantitatively fitted by the BCS theory with a mean free path I(T) increasing rapidely below Tc. This I-increase in the frame of the BCS-theory is limited at Ta by inelastic surface scattering at weak or strong links, e.g., by twin boundaries in distances aTW which dominates scattering for aTw2I(Ta). Below Ta the enforced energy transfer from YBCO-crystallites to weak links may enhance Z(Ta) until at T T* the weak link surface impedance dominates Zres(T相似文献
5.
C. T. Rieck K. Scharnberg S. Hensen G. Müller 《Journal of Low Temperature Physics》1996,105(3-4):503-508
The surface impedance of two 350nm thick YBCO films was measured for temperatures between 4.2K and 150K in a copper cavity at 87 GHz. Both films, one grown by electron beam evaporation on MgO, the other one by high oxygen-pressure dc sputtering from a stoichiometric target on LaAlO3, provide critical temperatures of about 91K, low residual surface resistances of Rs(4.2K) < 1m and low specific resistivities in the normal state of (100K) < 85cm. The experimental data obtained on these two films are compared to a d-wave model of superconductivity which incorporates elastic and inelastic scattering. Good agreement between theory and the experimental results for both the surface resistance and the penetration depth in the whole temperature range is achieved for scattering phase shifts near 0.4 and order parameter amplitudes in the range of 20(0)/kBTc = 6.0 – 7.5 without subtracting an extrinsic residual surface resistance. 相似文献
6.
High-resolution measurements of are reported for liquid4He and3He-4He mixtures at saturated vapor pressures between 1.2 and 4.2 K with particular emphasis on the superfluid transition. Here is the mass density, the shear viscosity, and in the superfluid phase both and are the contributions from the normal component of the fluid (
n
and
n
). The experiments were performed with a torsional oscillator operating at 151 Hz. The mole fraction X of3He in the mixtures ranged from 0.03 to 0.65. New data for the total density and data for
n
by various authors led to the calculation of . For4He, the results for are compared with published ones, both in the normal and superfluid phases, and also with predictions in the normal phase both over a broad range and close to T. The behavior of and of in mixtures if presented. The sloped/dT near T and its change at the superfluid transition are found to decrease with increasing3He concentration. Measurements at one temperature of versus pressure indicate a decreasing dependence of on molar volume asX(3He) increases. Comparison of at T, the minimum of
n
in the superfluid phase and the temperature of this minimum is made with previous measurements. Thermal conductivity measurements in the mixtures, carried out simultaneously with those of , revealed no difference in the recorded superfluid transition, contrary to earlier work. In the appendices, we present data from new measurements of the total density for the same mixtures used in viscosity experiments. Furthermore, we discuss the data for
n
determined for4He and for3He-4He mixtures, and which are used in the analysis of the data. 相似文献
7.
M. D. Whitmore 《Journal of Low Temperature Physics》1984,56(1-2):129-139
Approximate analytic calculations of the functional derivative ofT
c
with respect to 2()F() for anisotropic superconductors are presented, with the primary purpose of identifying the determining material parameters. The square-well model for the phonon-mediated electron-electron interaction, the weak coupling limit (
c
/2T
c
1), and separable anisotropy are used. The general behavior of T
c
/2()F() is the same as that found in numerical calculations for the case of small anisotropy, a
2/(–*)1; the regime of * is also discussed. 相似文献
8.
A new method to measure the thermal diffusivity of liquids is presented. It requires determination of the time dependence of the thermal expansion of the liquid when it is subjected to a heat source at the top of the cell containing the liquid. The high accuracy of the method (about 3%) is due to an essential reduction of convective currents and also to the absence of temperature detectors, which generally introduce unwanted perturbations on the thermal Field.Nomenclature
Thermal conductivity
-
c
Specific heat
-
Density
-
c = specific heat x density
-
h
Newton coefficient
-
Thermal diffusivity
-
T, 0
Temperature
-
tV
Electric signal
-
Calibration coefficient
- exp, th
Volume change of the liquid 相似文献
9.
A. A. El-Hamalaway 《Journal of Superconductivity》1993,6(5):305-311
The high-T
c
phase in the Y-Ba-Cu-O system was prepared and studied using specimens with various Y/Ba ratios. The d.c. conductivity was measured, and a theoretical relation between the normalized resistance and temperature at different polaron stabilization energies was taken into account to study the behavior of superconductor materials in the normal state. The 0.5 [Y/Ba] 1 and 3 [Y+Ba] 4 were found to be the most preferential ranges for the formation of a single superconducting phase. 相似文献
10.
K. C. Lim J. D. Thompson Bart Olinger L. R. Newkirk 《Journal of Low Temperature Physics》1981,45(5-6):575-580
We have determined the effect of hydrostatic pressureP on the superconducting transition temperatureT
c of bulk, A15 Nb3Si. For 0P20 kbar (2 GPa),T
c decrease linearly with increasing pressure at a rate T
c/P=–2.67×10–5 K/bar. From an estimate of T
c/P obtained using recent band structure calculations for the density-of-electronic-states change as a function of lattice parameter in Nb3Si, we conclude that the pressure dependence of the electron-phonon interaction primarily determines T
c/P.Work performed under the auspices of the U.S. DOE. 相似文献
11.
M. A. Hein A. Cassinese S. Hensen T. Kaiser G. M¨ller M. Perpeet 《Journal of Superconductivity》1999,12(1):129-138
Surface impedance data at 19 and 87 GHz of high-quality epitaxial YBCO films on different substrates are compared with data for Nb3Sn films on sapphire in terms of pair and quasiparticle (qp) transport. Surface resistance R
s and penetration depth of YBCO are strongly affected by temperature dependent qp scattering, which is depressed in films with enhanced lattice strain. All films showed a comparable residual resistance R
res(19 GHz)90 constituting a qp reservoir which is likely to be caused by the electronic configuration and by impurities. Subtracting R
res from R
s
(T) revealed activated behavior with a reduced energy gap 0/k
B
T
c0.9 for a film on sapphire, but power-law behavior for the other films. The penetration depth did not reveal power-law dependences at T0.5 ·T
c, but was consistent with a reduced energy gap of 0.45 for a film on MgO. The increase of (T) at T0.5 · T
c was related to qp scattering, which also caused an extremal conductivity 1(T). A shoulder in (T) at T=(0.6–0.7) · T
c confirmed evidence for the existence of two superconducting bands. The magnetic-field induced recovery of (B) of various YBCO films hinted for an important role of magnetic scattering. The results are in contradiction to a d-wave symmetry of the order parameter, at least for the chain band. 相似文献
12.
M. Ido T. Kudo N. Yamada N. Momono N. Abe T. Nakano C. Manabe M. Oda 《Journal of Low Temperature Physics》1996,105(3-4):311-316
In La2–xBaxCuO4 (LBCO) and La1.8–xNd0.2BaxCuO4 (LNBCO), the low-temperature structural change at T1 (=60–110K), resulting from tilt of the CuO6 octahedra, is easily suppressed at high pressures. However, the structural change of LNBCO (x=0.125) remains up to 2GPa though it jumps from T1(110K) to T* (60K), where the electric resistivity begins to upturn, at 0-1.5GPa. The upturn of is also suppressed at high pressures, and the superconducting critical temperature Tc is fully restored except in a very narrow x-range around x=0.125. The Tc for x 0.125 is appreciably lower at 2GPa than those for other Ba-contents. 相似文献
13.
Yu. A. Kirichenko S. M. Kozlov K. V. Rusanov E. G. Tyurina 《Journal of Engineering Physics and Thermophysics》1982,42(1):1-6
The effect of pressure and underheating on the position of the boundary between heat-transfer regimes in liquid helium and hydrogen is investigated.Notation q
heat flux
- p
pressure
- =Ts–T
underheating
- Ts
saturation temperature
- T
temperature of liquid
- T=Twa – T
Ts=Twa – Ts
- Twa
temperature of heat-emitting surface
- A,a, B, b, C
constants
- m, n
indices
- Nu
Nusselt number
- Ra
Rayleigh number
-
thermal conductivity
-
coefficient of cubical expansion
-
kinematic viscosity
- g
acceleration
-
standard deviation
Indices 01
conditions of convection-boiling transition
- 02
conditions of boiling-convection transition
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 1, pp. 5–11, January, 1982. 相似文献
14.
The enhancement ofT
c in Pb-Bi-Sn and Pb-Bi-In system alloy filaments produced by glass-coated melt spinning was investigated as a means of producing a new type of superconducting filament with highT
c. Long filaments of Pb-Bi-Sn alloy withT
c higher than 10 K and Pb-Bi-In alloy withT
c higher than 9 K were obtained from the molten state at a temperature of 1500 K with a winding speed of 2.63 m sec–1. For example, a Pb45Bi35Sn20 filament withT
c of 10.1 K was 15 m in diameter and polycrystalline with a grain size of 100 nm. The structure of the filament was a mixture of , tin and bismuth phases and a metastable phase of mixed structure of bismuth and supersaturated solid solution of tin in -phase was detected. TheT
c of the filament decreased on heat treatment. A metastable phase of mixed structure of bismuth and -phase was also detected for a Pb45Bi45In10 filament withT
c of 9.3 K. As the metastable phase for the Pb-Bi-In filament was more unstable than that for the Pb-Bi-Sn filament, theT
c of the filament was drastically decreased by heat treatment. The metastable phase was considered to play an important role in the enhancement ofT
c for Pb-Bi-Sn and Pb-Bi-In alloy filaments. 相似文献
15.
Tetsuya Yokoo Masatoshi Arai Yu Shiohara Setsuko Tajima Chris D. Frost Yasuo Endoh 《Journal of Low Temperature Physics》2003,131(3-4):731-735
The resonance and incommensurate peaks in optimally doped high-T
c superconductor YBa2Cu3O6.9 are observed by means of TOF neutron scattering technique. Obtained overall dynamical properties in a wide Q-E space show distinct incommensurate structure around antiferromagnetic (AF) zone center (, ). The incommensurability of =0.1 at 36 meV corresponds to the previous triple-axis neutron measurement. Variation of temperature dependence suggests the spectral weight of antiferromagnetic fluctuation observed around 25 meV at (, ) shifts to resonance peak position below T
c. Moreover obtained results with E
i=80 meV neutron energy indicate new feature of dynamical incommensurate structure at higher frequency region up to 53 meV. 相似文献
16.
The phonon dispersion of oxygen doped La2CuO4 + has been investigated by inelastic neutron scattering on a large single crystal with 0.02 (Tc = 31 K). Most of the phonons were found to be very similar to those of La1.9Sr0.1CuO4. However, in measurements of a phonon branch which exhibits a pronounced anomaly in (La, Sr)2CuO4 a two-peak structure was observed: one series of peaks corresponds to the phonon frequencies of undoped La2CuO4, the other one to that of La2–xSrxCuO4 with x 0.1. This finding is presumably associated with a phase separation into domains with low and high , respectively. 相似文献
17.
We have solved the Eliashberg gap equations which are valid for arbitrary phonon frequency, (ph), electron-phonon coupling constant, (), and screened Coulomb interaction, (
*). We have used values of (ph),, and (
*) appropriate to the cuprate superconductors, and calculated the density of states, the pair potential., and the value of the gap at T=0 K. Using the linearized Eliashberg equations in the matrix representation, we have calculatedT
c
and 2/k T
c
. We have found that we can account for the highT
c
's in the cuprates with reasonable values for,
*, and ph. 相似文献
18.
Lin Li Bai-ru Zhao Ping Zhou Shou-quan Guo You-xiang Zhao 《Journal of Low Temperature Physics》1981,45(3-4):287-294
The dependence of Tc on sputtering conditions, chemical composition, and phase structure for Nb-Ge films has been studied. It was found that Tc varied with composition, but was not dependent on exact stoichiometry of the film; the Nb/Ge ratio was <3 for very high Tc 23 K films and 4 for films with Tc 20 K. X-ray results showed that the films with Tc 23 K contained a certain amount of tetragonal Nb5Ge3 with a lattice parameter of A15 phase 5.14 Å. The depth profile of very high Tc films showed no increase of oxygen concentration at the film-substrate interface; no correlation of high Tc and impurities was found. 相似文献
19.
A method based on Landau's Fermi-fluid theory is presented for calculating the temperature-dependent viscosity and thermal conductivity of a Fermi fluid. It is argued that both O(T) and O(T2 ln T) terms appear in the temperature series expansions for T
2 and T. Exact expressions for the zero-temperature limit of T
2 and T are derived for the dilute hard-sphere Fermi gas (DHSFG). The leading finite-temperature corrections to these quantities due to the s dependence of the quasiparticle scattering amplitude are also derived for the DHFSG (s is a dimensionless ratio of energy transfer to momentum transfer). The results are compared with previous expressions of Emery and of Dy and Pethick; some discrepancies are noted and discussed.Based in part on a Ph.D. thesis by J.C.R. submitted to the University of Colorado. 相似文献
20.
A. A. Aleksandrov Z. A. Ershova 《Journal of Engineering Physics and Thermophysics》1981,40(5):555-557
Compact and precise equations are obtained for the saturation curves of normal and heavy water.Notation p
saturated vapor pressure
- pc
critical pressure
- T
absolute temperature
- Tc
critical temperature
- =T/Tc
dimensionless temperature
- =1 – ; r
heat of vaporization
- c
p
0
isobaric heat capacity of vapor in ideal gas state
- cs
liquid heat capacity along saturation curve
- v
specific volume of vapor
-
a
i
coefficients of Eq. (1)
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 5, pp. 894–897, May, 1981. 相似文献