title: Specific heat of Mg11B2: evidence for a second energy gap.
abstract: Measurements of the specific heat of Mg11B2 from 1 to 50 K, in magnetic fields to 9 T, give the Debye temperature, Theta = 1050 K, the coefficient of the normal-state electron contribution, gamma(n) = 2.6 mJ mol(-1) K-2, and a discontinuity in the zero-field specific heat of 133 mJ mol(-1) K-1 at T(c) = 38.7 K. The estimated value of the electron-phonon coupling parameter, lambda = 0.62, could account for the observed T(c) only if the important phonon frequencies are unusually high relative to Theta. At low T, there is a strongly field-dependent feature that suggests the existence of a second energy gap, about 4 times smaller than the major gap.
authors.affiliation: Lawrence Berkeley National Laboratory and Department of Chemistry, University of California, Berkeley, California 94720, USA.
authors.forename: F
authors.initials: F
authors.lastname: Bouquet
authors.forename: R A
authors.initials: RA
authors.lastname: Fisher
authors.forename: N E
authors.initials: NE
authors.lastname: Phillips
authors.forename: D G
authors.initials: DG
authors.lastname: Hinks
authors.forename: J D
authors.initials: JD
authors.lastname: Jorgensen