Nonsaturating linear resistivity up to 900 K inMgB2

Abstract

In this work, we report resistivity measurements on MgB 2 polycrystalline samples with increasing degree of doping ͑disorder͒ up to temperatures higher than 900 K. In all cases the normal state curves are linear with increasing temperatures, with no sign of flattening or downward bending ͑saturation͒ at high temperature. This behavior, in sharp contrast to what is observed in superconducting compounds such as A15 and Chevrel phases, can be explained considering the dominant contribution to the electric conduction, together with the smaller electron-phonon coupling of carriers in MgB 2 , as compared to characteristic coupling strength of those compounds. This indicates that in MgB 2 the disorder introduced in the lattice by thermal oscillations even at 900 K can still be considered as a perturbation within the Boltzmann description of transport.

Anisotropic phase diagram and superconducting fluctuations of single-crystalline SmFeAsO0.85F0.15

“…From magneto-transport data on polycrystalline samples [21] good -possibly fortuitous -agreement with that obtained from the fit in Fig. 3.…”

Magnetic-superconducting phase boundary ofSmFeAsO1−xFxstudied via muon spin rotation: Unified behavior in a pnictide family

“…This dictates a superconducting mean domain size of a few nanometers, compatible with an average coherence length of order = 2 nm. 29 The nanoscopic coexistence and the suppression of the ordering temperatures, a typical finite-size effect, are both indicative of a phase separation with extremely small domains, which suggests a strong competition between the two order parameters.…”

LargeD−2Theory of Superconducting Fluctuations in a Magnetic Field and its Application to Iron Pnictides

“…Recent experiments on SmFeAsO 1−x F x [26] suggest that the fluctuation conductivity follows an approximate 2D scaling behavior of the form predicted by Ref. [14] (see also Ref.…”

“…3 shows K(g) and the data for the optimally doped (x = 0.15, T c (0) = 51.5 K) sample at H = 28 T. The coherence length is ξ ab(c) (0) = 24 (3)Å [26]; the penetration depth λ ab(c) (0) = 2000 (16000)Å [28]; the upper critical field H c2 (0)/T c (0) = 7.8 T/K [29] fits snugly between |dH 10% c2 /dT | and |dH 90% c2 /dT | reported in Ref. [26]; and the interlayer separation s = 8.45Å [30]. One can see that the interlayer coupling leads to a strong enhancement of conductivity over its 2D form, even for modest values ofη/α 0 .…”

“…with g0 = 3, h = 0.3, and tc2(h) = 1 − h. The three curves have interlayer coupling values ofη/α0 = 0 (solid), 0.002 (dashed), and 0.004 (dotted). Fluctuation conductivity data from Ref [26],. along with a theoretical fit, with scaling variable g from (16), g0 = 6.37, andη/α0 = 0.022 (solid line).…”