Systematic characterization of upper critical fields for MgB₂thin films by means of the two-band superconducting theory

Abstract

We present experimental results of the upper critical fields Hc2 of various MgB2 thin films prepared by the molecular beam epitaxy, multiple-targets sputtering, and co-evaporation deposition apparatus. Experimental data of the Hc2(T ) are successfully analyzed by applying the Gurevich theory of dirty two-band superconductivity in the case of Dπ/Dσ > 1, where Dπ and Dσ are the intraband electron diffusivities for π and σ bands, respectively. We find that the parameters obtained from the analysis are strongly correlated to the superconducting transition temperature Tc of the films. We also discuss the anormalous narrowing of the transition width at intermediate temperatures confirmed by the magnetoresistance measurements.

Intraband scattering rate and electronic diffusivity study in MgB2bulk samples

“…Since the angular dependence of the diffusivities can be written as (1.9 ± 0.4) × 10 −2 m 2 s −1 , η Bc2 = 88 ± 21 for the SiC-doped sample #B3. The diffusivity values of the two bands as well as their ratios are consistent with the upward curvature near T c of the B c2 versus T curves [38], with the T c values [58] and with previous studies on bulk and single crystals [59,56,60]. Anyway further investigations are planned in order to verify if the B c2 versus T curves keep their positive curvature in the overall temperature range [61].…”

Strong magnetic field dependence of critical current densities and vortex activation energies in an anisotropic clean MgB2 thin film

“…In that case, the films exhibit large values of H c2 as well as changes in γ from 1 to 2 with decreasing temperature. [11,28] , Fig. 2(a) shows superconducting vortices in the MgB 2 film resolved by MFM as bright spots, a result of a repulsive interaction between the tip and the vortices, with magnetization antiparallel to each other.…”

Spontaneous symmetry breaking in vortex systems with two repulsive lengthscales

“…Experimental H c2 (T) data for a number of MgB 2 thin-films have previously been successfully analysed within a theory of dirty two-band superconductivity due to Gurevich, in which impurity scattering is introduced via intraband electron diffusivities, D π , D σ , and the interband scattering parameter, g 23 . Following the approach of Noguchi et al 24 , we choose the fixed intraband ( λ ππ , λ σσ ) and interband coupling constants ( λ πσ , λ σπ ) as 0.285, 0.81, 0.09 and 0.119 respectively, and calculate g ( T c ) for our films to be g 77nm = 0.44 and g 160nm = 0.081, confirming that there are significantly higher levels of scattering in the 77 nm film.…”