Anisotropic upper critical field in single crystal MgB2
Recent experiments on MgB2 single crystals appear to indicate that superconductivity in this material is described not only by two superconducting order parameters attached to the sigma band and the pi band, respectively, but also these two order parameters have different anisotropy. More explicitly the anisotropy of H-c2(t) requires an oblate order parameter in momentum space attached to the sigma band while H-c1 (t) is described by a prolate order parameter, attached to the pi band. Therefore the vortex state in MgB2 should be described by an interplay of these two superconducting order parameters.
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1199-1204
Springer-Verlag