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在Гинэбург-Ландау理论中借引入顺磁能导出了第二类超导体的临界磁场公式。理论公式与Ti-V合金系统的实验数据符合。考虑了顺磁能的影响之后,第二类超导体由“混合态”向正常态的转变仍为二级相变;在相变点附近,磁化曲线仍为直线;在强磁场中相变时的比热跳跃与零场中的比热跳跃同数量级;与V3Ga的比热测量及Nb3Sn的磁化曲线测量很好地符合。 相似文献
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报道了利用蓝宝石介质谐振器技术测量MgB2超导薄膜的微波表面电阻Rs sub>、0K时的穿透深度λ(0)和超导能隙Δ(0).λ(0)和Δ(0)的值是通过先测量样品穿透深度λ(T)的变化量Δλ(T),然后由BCS理论模型拟合Δλ(T)的实验数据得到的.测试样 品是利用化学气相沉积技术在MgO(111)基片上制备的c轴织构的MgB2超导薄膜, 薄膜的超导转变温度和转变宽度分别为38K和01K.微波测试结果表明在10K,18GHz下M gB2薄膜的Rs约为100μΩ,可以和高质量的YBCO薄膜的Rs值相比拟;BCS理论拟合得到的MgB2超导薄膜的λ(0)=102nm,Δ(0)=113k Tc. 相似文献
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本文用强耦合超导理论研究了金属氢的一些超导性能,求出了具有超导性的金属氢的同位素效应值,热力学临界磁场,比热和Tc,Hc及Δ对有效声子谱α2F(ω)的泛函导数:dTc/dα2F(ω),dHc/dα2F(ω)和d(2Δ/kBTc)/dα2F(ω)等与ω的关系曲线,说明超导性的一些参数与金属氢的电子-声子作用的关系。 相似文献
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利用自洽半经典(SCSC)计算确定的基态核子分布,讨论了电模式isovector巨共振性质.特别是,我们不仅考虑了ΔT3=0的模式,而且考虑了ΔT3=±1模式,从而讨论了此类巨共振的同位旋性质,给出了它们的增强因子及Centroid能量的同位旋分裂.其中增强因子和HF+RPA计算结果相一致,而Centroid能量的同位旋分裂则和实验事实相近. 相似文献
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《Solid State Communications》1987,64(5):685-687
The specific heat of single phase YBa2Cu3O7-δ has been measured using non-adiabatic method between 4.2K and 120K. There is a specific heat anomaly Δc at 90K (about 3.2% of total specific heat) approximately, due to superconducting transition. From the measured value of ΔC and transition temperature Tc, the electronic density of state at Fermi level N(EF) and Sommerfeld parameter γ calculated are 2.55±0.30states/eV.Cu-atom and 2.77±0.30 mJ/mole.K2, respectively. The experimental result of N(EF) is consistent with that of the band calculation by Mattheiss. The Debye temperature above Tc in this material deduced from Debye function is about 340K. Below 20K, the relation C=γ'T+βT3 is satisfied. But the value of γ' is smaller. That means, most of the electrons have formed superconducting Cooper pairs which give no contribution to specific heat below 20K. 相似文献
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《Solid State Communications》1987,64(2):247-251
Thermal and magnetic measurements have been performed on several YBa2Cu3O7−δ compounds, some ones showing a large content of high Tc (93 K) superconducting phase. A jump in the specific heat ΔCp, is well evidenced at the transition allowing a determination of the ratio ΔCp/Tc ≅ 23 ± 5. mJ/ (mole Cu)K2. In addition, an estimation of the γ value (≅ 11 mJ/(mole Cu). K2) has been drawn from the determination of the electronic entropy at Tc. The samples have been characterized by susceptibility, magnetization and resistivity experiments. The critical field slopes at Tc were found to be dHc1/dT ≅ 17 Oe/K and dHc2/dT ≅ 20 kOe/K. The results are discussed in the framework of the Ginzburg-Landau theory. 相似文献
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Darshan C. Kundaliya 《Solid State Communications》2004,131(8):489-491
The intermetallic compound, YRhAl, has been prepared and is found to be isomorphic with RRhAl (R=Pr, Nd, Gd, Ho and Tm) compounds crystallizing in the orthorhombic TiNiSi-type structure (space group Pnma). Heat capacity and electrical resistivity measurements in the He-3 temperature range reveal that this compound is superconducting with a transition temperature, Tc, of 0.9 K. The electronic specific heat coefficient, γ, and the Debye temperature are found to be 6.1 mJ/mol K and 197 K, respectively. The specific heat jump at the superconducting transition is found to be consistent with the BCS weak-coupling limit. This combined with the earlier observation of superconductivity in LaRhAl (Tc=2.4 K) having a different structure than that of YRhAl, suggests that the underlying structure is not very crucial for the occurrence of superconductivity in RRhAl series of compounds. 相似文献
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L. G. Mamsurova K. S. Pigalskiy N. G. Trusevich A. A. Vishnev M. A. Rogova S. Yu. Gavrilkin A. Yu. Tsvetkov 《JETP Letters》2015,102(10):662-667
The magnetization M(H) in the superconducting state, dc magnetic susceptibility χ(T) in the normal state, and specific heat C(T) near the superconducting transition temperature T c have been measured for a series of fine-crystalline YBa2Cu3O y samples having nearly optimum values of y = 6.93 ± 0.3 and T c = (91.5 ± 0.5) K. The samples differ only in the degree of nanoscale structural inhomogeneity. The characteristic parameters of superconductors (the London penetration depth and the Ginzburg–Landau parameter) and the thermodynamic critical field H c are determined by the analysis of the magnetization curves M(H). It is found that the increase in the degree of nanoscale structural inhomogeneity leads to an increase in the characteristic parameters of superconductors and a decrease in H c(T) and the jump of the specific heat ΔC/T c. It is shown that the changes in the physical characteristics are caused by the suppression of the density of states near the Fermi level. The pseudogap is estimated by analyzing χ(T). It is found that the nanoscale structural inhomogeneity significantly enhances and probably even creates the pseudogap regime in the optimally doped high-T c superconductors. 相似文献
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P. Entel 《Solid State Communications》1976,19(12):1233-1235
The upper critical field Hc2(T) and the specific heat jump ΔC(Tc) are calculated for Cs0.1WO2.9F0.1 using a two-band model. The model parameters are obtained by adjusting the theoretical Hc2(T) values to experimental results. The model calculation predicts an anomalous specific heat jump ΔC as a function of the inverse relation Tc(H). 相似文献
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Mohamed El-Genk 《实验传热》2013,26(4):281-301
The effects of orientation and subcooling on pool boiling of the HFE-7100 dielectric liquid near atmospheric pressure (0.085 MPa) from a 10 × 10 mm smooth copper surface are investigated experimentally. Results are obtained for inclination angles θ = 0° (upward-facing), 30°, 60°, 90°, 120°, 150°, and 180° (downward-facing) and liquid subcoolings ΔTsub = 0, 10, 20, and 30 K. Increasing θ decreases the saturation nucleate boiling heat flux at high surface superheats (ΔTsat > 20 K), but increases it only slightly at lower surface superheats. The critical heat flux (CHF) decreases slowly with increasing θ from 0° to 90°, and then deceases faster with increasing θ to 180°. CHF increases linearly with increased subcooling, but the rate increases from 0.016 K?1 at 0° to 0.048 K?1 at 180°. At θ = 0° and ΔTsub = 30 K, CHF is ~ 36 W/cm2 and 24.45 W/cm2 for saturation boiling, while at θ = 180° CHF = 10.85 W/cm2 at ΔTsub = 30 K and only 4.30 W/cm2 at saturation. The developed correlation for CHF of HFE-7100, as a function of θ and ΔTsub, is within ±10% of the present data. The recorded still photographs of the boiling surface in the experiments illustrate the effects of liquid subcooling and surface orientation at different nucleate boiling heat fluxes and surface superheats on vapor bubble accumulation and/or induced mixing at the surface. 相似文献
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Giuseppina Ceccorulli Maria Pizzoli Giovanni Pezzin 《Journal of Macromolecular Science: Physics》2013,52(4):499-510
Samples of poly(vinyl chloride) polymerized at temperatures from ?60°C to +90°C, and therefore of different degrees of syndiotacticity and crystallinity, have been thermally treated in an attempt to reduce their content of ordered structures. Changes in order have been monitored by measuring Tg and the corresponding specific heat increment Δcp. Partially syndiotactic samples have higher Tg and lower Δcp than samples that are nearly atactic. After thermal treatment the differences decrease but do not vanish, even for samples heat-treated to about 250°C. This seems to indicate that some ordered structures are very stable even at relatively high temperatures. A quantitative estimate of the ordered structure content, based on Δcp data, is proposed. 相似文献
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Specific heat measurements between 0.5 and 4.2°K are reported for the system (, Gd) Al2 in both the superconducting and normal state. The observed specific heat jump at the superconducting transition temperature Tc is in excellent agreement with the Abrikosov-Gor'kov (AG) theory. This is in accordance with the previously reported close correspondence of the Tc vs. Gd concentration curve with the AG theory. Two very interesting features occur in the normal state specific heat. First, the Gd impurities cause a surprisingly strong enhancement of the electronic specific heat coefficient. Second, there is a large magnetic field dependent Schottky-like anomaly at low temperatures. This anomaly persists even in the superconducting state. 相似文献
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In this article, we studied the specific heat data of iron-based superconductors LaO1? x F x FeAs (x?=?0.1) and SmO1? x F x FeAs (x?=?0.13,?0.12, and 0.1). (i) The contribution of phonons in specific heat above Tc depends exponentially on temperature. (ii) The specific heat has different contributions, and they change differently at Tc . This change must be the effect of a physical function on heat capacity. Therefore, transition temperature is defined by thermal parameters. For LaO0.9F0.1FeAs and SmO0.87F0.13FeAs, a transition point was evaluated at 22.11 and 26.32?K, respectively. This is in close agreement with the midpoint transition temperatures obtained from dc resistivity and magnetization experiments, where the modified electronic heat capacity led to the approximate value of the transition point in two samples. The jump, ΔC/γT c, and the electronic and lattice heat capacity coefficients, γ and β, respectively, were evaluated. 相似文献