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Register a new userDo organic and other exotic superconductors fail universal scaling relations?
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Universal scaling relations are of tremendous importance in science, as they reveal fundamental laws of nature. Several such scaling relations have recently been proposed for superconductors; however, they are not really universal in the sense that some important families of superconductors appear to fail the scaling relations, or obey the scaling with different scaling pre-factors. In particular, a large group of materials called organic (or molecular) superconductors are a notable example. Here, we show that such apparent violations are largely due to the fact that the required experimental parameters were collected on different samples, with different experimental techniques. When experimental data is taken on the same sample, using a single experimental technique, organic superconductors, as well as all other studied superconductors, do in fact follow universal scaling relations.
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We propose and show that the c-axis transport in high-temperature superconductors is controlled by the pseudogap energy and the c-axis resistivity satisfies a universal scaling law in the pseudogap phase. We derived approximately a scaling function for the c-axis resistivity and found that it fits well with the experimental data of Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$, Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+delta}$, and YBa$_2$Cu$_3$O$_{7-delta}$. Our works reveals the physical origin of the semiconductor-like behavior of the c-axis resistivity and suggests that the c-axis hopping is predominantly coherent.
The Aharonov-Casher effect is the analogue of the Aharonov-Bohm effect that applies to neutral particles carrying a magnetic moment. This can be manifested by vortices or fluxons flowing in trajectories that encompass an electric charge. These have been predicted to result in a persistent voltage which fluctuates for different sample realizations. Here we show that disordered superconductors exhibit reproducible voltage fluctuation, antisymmetrical with respect to magnetic field, as a function of various parameters such as magnetic field amplitude, field orientations and gate voltage. These results are interpreted as the vortex equivalent of the universal conductance fluctuations typical of mesoscopic disordered metallic systems. We analyze the data in the framework of random matrix theory and show that the fluctuation correlation functions and curvature distributions exhibit behavior which is the fingerprint of Aronov-Casher physics. The results demonstrate the quantum nature of the vortices in highly disordered superconductors both above and below $T_c$.
The electrical resistivity of the quasi-1D organic superconductor (TMTSF)2PF6 was recently measured at low temperature from the critical pressure needed to suppress the spin-density-wave state up to a pressure where superconductivity has almost disappeared. This data revealed a direct correlation between the onset of superconductivity at Tc and the strength of a non-Fermi-liquid linear term in the normal-state resistivity, going as r(T) = r0 + AT + BT2 at low temperature, so that A goes to 0 as Tc goes to 0. Here we show that the contribution of low-frequency antiferromagnetic fluctuations to the spin-lattice relaxation rate is also correlated with this non-Fermi-liquid term AT in the resistivity. These correlations suggest that anomalous scattering and pairing have a common origin, both rooted in the low-frequency antiferromagnetic fluctuations measured by NMR. A similar situation may also prevail in the recently-discovered iron-pnictide superconductors.
Scaling laws express a systematic and universal simplicity among complex systems in nature. For example, such laws are of enormous significance in biology. Scaling relations are also important in the physical sciences. The seminal 1986 discovery of high transition-temperature (high-T_c) superconductivity in cuprate materials has sparked an intensive investigation of these and related complex oxides, yet the mechanism for superconductivity is still not agreed upon. In addition, no universal scaling law involving such fundamental properties as T_c and the superfluid density rho_s, a quantity indicative of the number of charge carriers in the superconducting state, has been discovered. Here we demonstrate that the scaling relation rho_s propto sigma_{dc} T_c, where the conductivity sigma_{dc} characterizes the unidirectional, constant flow of electric charge carriers just above T_c, universally holds for a wide variety of materials and doping levels. This surprising unifying observation is likely to have important consequences for theories of high-T_c superconductivity.
We report an easy route single step synthesis of BiOCuS with and without Cu deficiency. The title compound is synthesized via solid state reaction route by encapsulation in an evacuated (10-3 Torr) quartz tube. Mixed components of the ingredients in stoichiometric ratio (1/3Bi2O3 +0.34Bi +Cu1-x + S) are pelletized, sealed in evacuated quartz tube and heat treated for 30 hours at 500 0C. Finally the sample is allowed to cool down to room temperature. The resultant compound is black is color and could not hold in pellet form, but is powdered. X-ray diffraction Reitveld analysis is carried out on all three samples of series BiOCu1-xS with x = 0.0, 0.10 and 0.15. These samples crystallize in single phase with space group P4/nmm and with cell parameters as a = 3.868 A and c = 8.557 A for stoichiometric BiOCuS. The volume of the cell slightly increases with an increase in Cu deficiency. The co-ordinate positions are determined by fitting the observed XRD patterns of the studied samples.
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