Carrier Transport in Nano-Inclusioned Magnesium Diboride
Despite multiband systems' complexities, the sheer absence of any expected or novel anomaly at the superconducting transition in thermal transport data of MgB2 has been a matter of sustained investigations spanning last decade. Double-band and anisotropic-gap effects ironed out the Tc-signature in predominantly electronic thermal conductivity, of somewhat low-resistivity specimens studied, leaving little scope for the negligible phononic anomaly-contribution to be manifested. We report thermal transport studies on scarcely explored nano-inclusioned MgB2 alloy, exhibiting clear superconducting transition; combining subdued-mobility-band charge transport with significant heat-conduction by phonons, dominantly scattered around Tc by the electrons. The self-formed MgO as extended defects here impart enhanced elastic scattering to the charge carriers, with milder effect on the phonon having longer mean free path near Tc. At higher temperatures however, due to their reduced dominant wavelength, phonons are strongly scattered by the nanoparticles; lattice heat transport undergoes ballistic to diffusive crossover, culminating in Ioffe-Regel mobility threshold.