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Register a new userTemperature dependences of the upper critical field and the Ginzburg-Landau parameter of Li2Pd3B from magnetization measurements
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We present temperature dependences of the upper critical magnetic field and the Ginzburg-Landau parameter for a ternary boride superconductor Li_2Pd_3B obtained from magnetization measurements. A specially developed scaling approach was used for the data analysis. The resulting H_c2(T) curve turns out to be surprisingly close to predictions of the BCS theory. The magnetic field penetration depth, evaluated in this work, is in excellent agreement with recent muon-spin-rotation experiments. We consider this agreement as an important proof of the validity of our approach.
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We present a short review of our studies of disorder influence upon Ginzburg - Landau expansion coefficients in Anderson - Hubbard model with attraction in the framework of the generalized DMFT+$Sigma$ approximation. A wide range of attractive potentials $U$ is considered - from weak coupling limit, where superconductivity is described by BCS model, to the limit of very strong coupling, where superconducting transition is related to Bose - Einstein condensation (BEC) of compact Cooper pairs, which are formed at temperatures significantly higher than the temperature of superconducting transition, as well as the wide range of disorders - from weak to strong, when the system is in the vicinity of Anderson transition. For the same range of parameters we study in detail the temperature behavior of orbital and paramagnetic upper critical field $H_{c2}(T)$, which demonstrates the anomalies both due to the growth of attractive potential and the effects of strong disordering.
Long-standing discrepancies within determinations of the Ginzburg-Landau parameter $kappa$ from supercritical field measurements on superconducting microspheres are reexamined. The discrepancy in tin is shown to result from differing methods of analyses, whereas the discrepancy in indium is a consequence of significantly differing experimental results. The reanalyses however confirms the lower $kappa$ determinations to within experimental uncertainties.
We apply Landau-Ott scaling to the reversible magnetization data of Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$ published by Y. Wang et al. [emph{Phys. Rev. Lett. textbf{95} 247002 (2005)}] and find that the extrapolation of the Landau-Ott upper critical field line vanishes at a critical temperature parameter, T^*_c, a few degrees above the zero resistivity critical temperature, T_c. Only isothermal curves below and near to T_c were used to determine this transition temperature. This temperature is associated to the disappearance of the mixed state instead of a complete suppression of superconductivity in the sample.
By comparison of recent direct measurements of the temperature dependence of the upper critical field $H_{c2}$ in an Y-123 high temperature superconductor with the scaling analysis of magnetization data, collected in fields H << H_c2, we demonstrate that that the temperature dependence of the Ginzburg-Landau parameter kappa is negligible. Another conclusion is that the normalized temperature dependence of H_c2 is independent of the orientation of the magnetic field in respect to crystallographic axes of the sample. We also discuss that isotropy of the temperature dependence of H_c2 straightforwardly follows from the Ginzburg-Landau theory if kappa does not depend on temperature.
We present measurements of the superconducting critical temperature Tc and upper critical field Hc2 as a function of pressure in the transition metal dichalcogenide 2H-NbS2 up to 20 GPa. We observe that Tc increases smoothly from 6K at ambient pressure to about 8.9K at 20GPa. This range of increase is comparable to the one found previously in 2H-NbSe2. The temperature dependence of the upper critical field Hc2(T) of 2H-NbS2 varies considerably when increasing the pressure. At low pressures, Hc2(0) decreases, and at higher pressures both Tc and Hc2(0) increase simultaneously. This points out that there are pressure induced changes of the Fermi surface, which we analyze in terms of a simplified two band approach.
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