Temperature-dependent anisotropy of the penetration depth and coherence length of MgB2 -: art. no. 097005

We report measurements of the temperature-dependent anisotropies (gamma(lambda) and gamma(xi)) of both the London penetration depth lambda and the upper critical field of MgB2. Data for gamma(lambda)=lambda(c)/lambda(a) was obtained from measurements of lambda(a) and lambda(c) on a single crystal sample using a tunnel diode oscillator technique. gamma(xi)=H-c2(perpendicular to c)/H-c2(parallel to c) was deduced from field-dependent specific heat measurements on the same sample. gamma(lambda) and gamma(xi) have opposite temperature dependencies, but close to T-c tend to a common value (gamma(lambda)similar or equal to gamma(xi)=1.75 +/- 0.05). These results are in good agreement with theories accounting for the two-gap nature of MgB2.