Measurements were made of the temperature-dependent anisotropies, γλ and γχ, of both the London penetration depth, λ, and the upper critical field of MgB2. Data for γλ = λC/λa was obtained from measurements of λa and λC on a single crystal sample using a tunnel diode oscillator technique. Here, γχ = HC2c/HC2||c was deduced from field-dependent specific heat measurements on the same sample. The γλ and γχ had opposite temperature dependences but, close to TC, tended to a common value, γλ, which was similar or equal to γχ = 1.75. These results were in good agreement with theories accounting for the 2-gap nature of MgB2.

Temperature-Dependent Anisotropy of the Penetration Depth and Coherence Length of MgB2. J.D.Fletcher, A.Carrington, O.J.Taylor, S.M.Kazakov, J.Karpinski: Physical Review Letters, 2005, 95[9], 097005 (3pp)