Intraband scattering rate and electronic diffusivity study in MgB₂bulk samples

Abstract

In this paper we present a combined analysis of the electron transport properties of polycrystalline MgB2 samples, both in the normal and in the superconducting state. This study is aimed at checking the applicability of multiband models to the evaluation of band conduction parameters as well as at addressing the role of some disorder typologies (Mg inclusions, low-level SiC doping) in affecting them. Normal-state resistivities, suitably rescaled to take into account the grain connectivity, were first analysed in the framework of the model formulated by Mazin et al (2002 Phys. Rev. Lett. 89 107002), where we introduced transport spectral functions calculated from the standard Eliashberg functions. The band scattering rates were obtained: the impurity σ band scattering rate was found to be weakly dependent on magnetic field in all the analysed samples and to increase with SiC doping. Accordingly, intraband diffusivities obtained by analysing the upper critical field in the framework of Gurevich’s model (2003 Phys. Rev. B 67 184515) show a decrease of the σ band diffusivity in the SiC-doped sample, whereas no remarkable doping effect was found in the π band.

Influence of nanoparticle doping on electronic properties of MgB2bulk samples

“…X-ray diffraction pattern reveals a small shift of the (hk0)-type MgB 2 peaks indicating a contraction of the a axis of the crystal lattice of about 0.10 %, as expected in presence of small C substitution on boron site [40]. No new phases, such as Mg 2 Si, BC or MgB 2 C 2 were detected [41]. This means that only a small fraction of carbon entered the MgB 2 cell whereas the remnant part of the dopant stayed located at the grain boundaries.…”

Normal and superconducting properties of LiFeAs explained in the framework of four-band Eliashberg theory

“…Phenomenological model [22] proposed to explain saturation at high temperature generally assume the presence of parallel conductivity channels where one of them has a strong temperature dependence and another one is characterized by a temperature-independent contribution. In the wake of the model proposed for the superconducting state, we propose a multiband model [23,24] for analyzing the resistivity data. We will examine two possible mechanism responsible of resistivity: Phonons and antiferromagnetic spin fluctuations.…”

“…We will examine two possible mechanism responsible of resistivity: Phonons and antiferromagnetic spin fluctuations. The theoretical expression of the resistivity as function of temperature [23,24] is given by the equation:…”

Effects influencing the grain connectivity in ex-situ MgB2 wires

“…One can see apparent differences in the values of normal state resistivities (q MgB2 ). Room temperature q MgB2 of presented cores is ranging from 75 to 300 lX cm, which is considerably higher than for MgB 2 films $10 lX cm [11] and for in situ bulk samples 20-50 lX cm [12]. The highest q MgB2 corresponds to sample A1 reflecting the lowest core purity.…”