Low-energy excitations, symmetry breaking and specific heat in YbBiPt

The heavy fermion compound YbBiPt has a very large linear coefficient of sp ecific heat gamma = 8 J mol(-1) K-2 and this is understood, to first order, in terms of the observed low-energy neutron scattering response. However? at low temperatures, symmetry forbidden splittings at 1 and 2 meV, respecti vely are observed. These levels give good qualitative agreement with the me asured specific heat, but poor quantitative agreement. Indeed, the specific heat drops more rapidly with temperature than can be accounted for assumin g a temperature-independent density of states. We also present new low-temp erature crystallographic data, which rule out any significant structural di stortions. (C) 1999 Elsevier Science B.V. All rights reserved.