PRESSURE EFFECTS ON TRANSPORT-PROPERTIES OF YB4AS3

We have investigated the transport properties and their pressure effects on Yb4As3, which shows a heavy Fermion property with extremely low carrier concentration. Temperature dependence of the resistivity and of the Hall coefficient under high pressure up to 1.2 GPa was measured in the temperature range from 4.2 K to 320 K. A remarkable change in both resistivity and the Hall coefficient was revealed under high pressure in the whole temperature range. The inverse Hall mobility was found to show no peak even under high pressure at the temperature where the resistivity and the Hall coefficient have a broad one. These results indicate that the carrier number changes drastically with temperature and pressure. We show that these anomalous behavior can be explained well by a two-band model at least in the low temperature region. This model suggests that a narrow band with high density of states reflecting the large gamma-value plays an important role on the transport properties in Yb4As3.