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.
@article{arxiv.cond-mat/0104574,
title = {Order parameter of MgB_2: a fully gapped superconductor},
author = {H. D. Yang and J. -Y. Lin and H. H. Li and F. H. Hsu and C. J. Liu and S. -C. Li and R. -C. Yu and C. -Q. Jin},
journal= {arXiv preprint arXiv:cond-mat/0104574},
year = {2009}
}
Comments
7 pages, 5 figures; revised text and figures; references updated, Phys. Rev. Lett., in press