Dresden 2006 – scientific programme
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TT: Tiefe Temperaturen
TT 18: Superconductivity: Borides, Borocarbides, Carbides, ...
TT 18.4: Talk
Tuesday, March 28, 2006, 15:45–16:00, HSZ 02
Specific heat of Mg(B1−xCx)2: Two Superconducting Gaps — •Niels Oeschler1,2, Robert A. Fisher1, Norman E. Phillips1, William E. Mickelson1, and Alex Zettl1 — 1University of California, Berkeley, CA, USA — 2Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
We present specific heat data of polycrystalline Mg(B1−xCx)2 with x=0.1 and 0.2 from 1K to 35K in magnetic fields up to 9T.
Recently, MgB2 was identified as a phonon-mediated two-gap superconductor with remarkably high transition temperature of 39K. The small gap and the large gap open at the same temperature due to interband coupling. Substituting carbon on the boron site has the effect of electron filling and inducing disorder. The superconducting transition temperature decreases monotonically from 39K for MgB2 to 20K for Mg(B0.8C0.2)2. The specific heat of both samples can be accurately fitted with two superconducting energy gaps using the extended α model. The amplitudes of the gaps are found to be larger than the BCS value for the large gap and smaller than the BCS value for the small gap. However, it is observed that the size of both gaps decreases upon increasing the carbon content.
The evolution of the gap sizes, the normal-state Sommerfeld coefficients, the Debye temperatures and the critical fields are compared to those of MgB2.