Specific heat in a magnetic field for the extremely low carrier system Yb 4As 3

Abstract

Yb 4As 3 has an extremely low carrier concentration, which is estimated to be 0.1% per Yb ion, from Hall coefficient and optical reflectivity measurements. The γ value for Yb 4As 3 has a value as large as 200 mJ/mole K 2 per Yb 3+ ion. This γ value, the extrapolated magnetic susceptibility at 0 K, and the coefficient of T 2 in the temperature dependence of the resistivity nearly satisfy the universal relations expected for the heavy fermions. It is hard to understand all these physical properties using a simple extension of the impurity Kondo conception. It is widely believed that Kondo or heavy-fermion systems require a lot of carriers to compensate the magnetic moment. The question is whether it is possible to have a heavy-fermion system with such a low carrier concentration. In order to try and answer this question, we measured the specific heat as a function of temperature, lowering it to 1.5 K, for magnetic fields up to 10 T. It was observed that the linear relation between C T and T 2 was broken by the magnetic field, and that a hump in the specific heat appeared at about 3 T. The position of this hump is shifted to higher T when the field is increased. The total entropy seems to be field independent at high temperatures.