Quantum critical phenomenon of CeS studied by electrical transport measurements under high pressure

Anomalous quantum critical behavior of CeS under high pressure has been studied by electrical resistivity and Hall resistivity measurements up to 7.2 GPa using a Bridgman-type anvil cell. The electrical resistivity increases significantly with decreasing temperature at high pressures, which is interpreted as an enhancement in the Kondo effect. However, the increasing curve does not follow the log T dependence and it is difficult to ascribe only to the normal Kondo effect due to spin fluctuation. The increase of resistivity at low temperatures on approaching the critical pressure of 5 GPa is anomalously large in comparison with those of other inter-metallic compounds such as CeIn₃. In addition, the resistivity increases even below T_N from 4.4 to 5.2 GPa, which is reminiscent of a gap opening. The measurement of Hall resistivity, however, shows no clear indication of such gap opening. We consider that a valence fluctuation, in addition to the normal spin fluctuation, plays an important role in the quantum criticality of CeS. (author)