Anisotropy parameters of superconducting MgB${}_2$

Abstract

Data on macroscopic superconducting anisotropy of MgB${}_2$ are reviewed. The data are described within a weak coupling two-gaps anisotropic s-wave model of superconductivity. The calculated ratio of the upper critical fields ${\gamma }_H=H_{c2,ab}/H_{c2,c}$ increases with decreasing temperature in agreement with available data, whereas the calculated ratio of London penetration depths ${\gamma }_{\lambda }={\lambda }_c/{\lambda }_{ab}$ decreases to reach $\approx 1.1$ at T=0. Possible macroscopic consequences of ${\gamma }_{\lambda }\ne {\gamma }_H$ are discussed.

accepted to Physica C, special MgB2 issue