title: 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 T(c) of MgB(2). Together with the small specific heat jump Delta C/gamma(n)T(c) = 1.09, scenarios such as anisotropic s-wave or multicomponent 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.
authors.affiliation: Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan, Republic of China.
authors.forename: H D
authors.initials: HD
authors.lastname: Yang
authors.forename: J Y
authors.initials: JY
authors.lastname: Lin
authors.forename: H H
authors.initials: HH
authors.lastname: Li
authors.forename: F H
authors.initials: FH
authors.lastname: Hsu
authors.forename: C J
authors.initials: CJ
authors.lastname: Liu
authors.forename: S C
authors.initials: SC
authors.lastname: Li
authors.forename: R C
authors.initials: RC
authors.lastname: Yu
authors.forename: C Q
authors.initials: CQ
authors.lastname: Jin