The effects of planar hole concentration, p, and in-plane disorder, Zn (y), on the DC resistivity, ρ(T), of sintered samples of Y 1-x Ca x Ba 2 (Cu 1-y Zn y ) 3 O 7-δ were investigated over a wide doping range by changing both the oxygen deficiency (δ) and Ca content (x). From the ρ(T,p) data we extracted characteristic crossover temperatures on the underdoped and overdoped sides, T * and T m respectively, above which ρ(T) is linear. We compare our results with a number of other polycrystalline, thin film and single crystal cuprate superconductors and find similar behavior in the p-dependence of T * (p), T m (p), and the resistivity exponent, m(p), in fits to ρ(T) = ρ 0 + aT m on the overdoped side.Our findings points towards the possible existence of a quantum critical point (QCP) at the doping p=0.19 ± 0.01.
Using first‐principles calculations, the structural, elastic, and electronic properties of MoAlB have been investigated. The optimized lattice constants exhibit fair agreement with the experimental results. The computed elastic constants satisfy the mechanical stability conditions for MoAlB. The Mo‐based boride MoAlB is elastically anisotropic and classified as brittle material. This boride is expected to be thermally conductive due to its high Debye temperature of 693 K. The metallic conductivity of this compound is predicted by means of electronic structure calculations. The chemical bonding in MoAlB is basically covalent that is assured with the results of DOS, Mulliken population, and charge density distribution. The hardness value of 11.6 GPa for MoAlB suggests that it is relatively soft compared to many others borides. The Fermi surface is formed due to low dispersive Mo 4d‐like bands, which makes the compound a conductive one.
A universal scaling relation, ρs ∝ σ(Tc) × Tc has been reported by Homes et al. (Nature (London) 430, 539 (2004)) where ρs is the superfluid density and σ(T ) is the DC conductivity. The relation was shown to apply to both c-axis and in-plane dynamics for high-Tc superconductors as well as to the more conventional superconductors Nb and Pb, suggesting common physics in these systems. We show quantitatively that the scaling behavior has several possible origins including, marginal Fermiliquid behavior, Josephson coupling, dirty-limit superconductivity and unitary impurity scattering for a d-wave order parameter. However, the relation breaks down seriously in overdoped cuprates, and possibly even at lower doping.
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