Anisotropic critical fields of MgB2 single crystals

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The recently discovered superconductivity in MgB2 has created the world sensation. In spite of the relatively high superconducting transition temperature Tc=39K, the superconductivity is understood in terms of rare two gap superconductor with energy gaps attached to the sigma- and pi-band. However, this simple model cannot describe the temperature dependent anisotropy in Hc2 or the temperature dependence of the anisotropic magnetic penetration depth. Here we propose a model with two anisotropic energy gaps with different shapes. Indeed the present model describes a number of pecularities of MgB2 which have been revealed only recently through single crystal MgB2.