DEHAAS-VANALPHEN STUDIES OF YBAS ABOVE AND BELOW NEEL TEMPERATURE

We have studied the Fermi surface and the cyclotron mass of a semimeta llic heavy fermion compound YbAs both in the antiferromagnetic state a nd the paramagnetic state. We have found the Fermi surface of three el lipsoidal electron surfaces and one spherical hole surface, and that t he shape of these Fermi surfaces is the same in both states. In additi on, we have found that the temperature dependence of the dHvA oscillat ory amplitudes change anomalously at the Neel temperature. This anomal y is ascribed to the change of the cyclotron mass and the Dingle tempe rature at the Neel temperature. To explain the large electronic specif ic heat coefficient, the extremely heavy hole surface with about 10(3) m0 should exist.