HEAVY-ELECTRON BEHAVIOR IN A LOW-CARRIER-CONCENTRATION COMPOUND YBAS

Low-temperature specific heat of YbAs has been measured down to about 50 mK. In the antiferromagnetic ordered state (T(N) approximately 0.5 K), the nuclear contribution is observed below about 150 mK. By subtraction of this contribution from the measured specific heat, the linear coefficient of the electronic specific heat is estimated to be about 270 mJ/K2 mole. This value is extraordinarily large because the carrier concentration in YbAs is of the order of 0.01 per formula unit. This large mass enhancement may be ascribed to a mutual 4f-spin compensation mechanism instead of the usual Kondo spin fluctuation. We also show that the magnetic field effect on the specific heat is rather small.