We have measured the low-temperature specific heat C(T) for polycrystalline MgB2 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 MgB2. Together with the small specific heat jump ΔC/γnTc = 1.09, scenarios such as anisotropic s-wave or multicomponent order parameter are called for. The magnetic field dependence of γ(H) is neither linear for a fully gapped s-wave superconductor nor H1/2 for nodal order parameter. It seems that this intriguing behavior of γ(H) is associated with the intrinsic electronic properties other than flux pinning.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)