Anisotropy of the superconducting state properties and phase diagram of MgB2 by torque magnetometry on single crystals

Abstract

The angular and temperature dependence of the upper critical field Hc2 in MgB2 was determined from torque magnetometry measurements on single crystals. The Hc2 anisotropy gamma_H was found to decrease with increasing temperature, in disagreement with the anisotropic Ginzburg-Landau theory, which predicts that the gamma_H is temperature independent. This behaviour can be explained by the two band nature of superconductivity in MgB2. An analysis of measurements of the reversible torque in the mixed state yields a field dependent effective anisotropy gamma_eff, which can be at least partially explained by different anisotropies of the penetration depth and the upper critical field. It is shown that a peak effect in fields of about 0.85 Hc2 is a manifestation of an order-disorder phase transition of vortex matter. The H-T phase diagram of MgB2 for H//c correlates with the intermediate strength of thermal fluctuations in MgB2, as compared to those in high and low Tc superconductors.

arXiv comment12 pages, 8 figures, Physica C in print (invited paper for a special issue on MgB2)

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Cited by in corpus (9)

• Carbon substitution in MgB2 single crystals: structural and superconducting properties
• The different development of the anisotropic upper critical field in MgB2 by aluminum and carbon doping
• Two-band Effects in the Angular Dependence of Hc2 of MgB2 Single Crystals
• Anisotropy and internal field distribution of MgB2 in the mixed state at low temperatures
• Damping of the de Haas-van Alphen oscillations in the superconducting state of MgB_2
• High-pressure high-temperature solution growth, structural, and superconducting properties of Fe-substituted MgB2 single crystals
• Abrikosov flux-lines in two-band superconductors with mixed dimensionality
• Comment on "Superconducting anisotropy and evidence for intrinsic pinning in single crystalline MgB2"
• Anisotropic properties of MgB2 by torque magnetometry