Order parameter of MgB_2: a fully gapped superconductor

Abstract

We have measured the low-temperature specific heat C(T) for polycrystalline MgB_2 prepared by high pressure synthesis. C(T) below 10 K vanishes exponentially, which unambiguously indicates a fully opened superconducting energy gap. However, this gap is found to be too small to account for Tc of MgB_2. Together with the small specific heat jump DeltaC/gamma_nTc=1.13, scenarios like anisotropic s-wave or multi-component order parameter are called for. The magnetic field dependence of gamma(H) is neither linear for a fully gapped s-wave superconductor nor H^1/2 for nodal order parameter. It seems that this intriguing behavior of gamma(H) is associated with the intrinsic electronic properties other than flux pinning.

7 pages, 5 figures; revised text and figures; references updated, Phys. Rev. Lett., in press

References in corpus (2)

• Boron Isotope Effect in Superconducting MgB${}_2$
• Thermodynamic and Transport Properties of Superconducting $M{g}^{10}{B}_2$

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