Anomalous pressure dependence of the electrical resistance and thermal expansion of UGe₂ in the paramagnetic state

The electrical resistivity of single-crystalline UGe₂ has been measured under high pressure. It is found that the pressure dependence of the electrical resistivity shows an anomaly around 1 GPa even in the paramagnetic temperature range above T_C = 52 K. But the anomaly disappears above 200 K. The thermal expansion of UGe₂ was also measured at high pressure to clarify the lattice properties. The thermal expansion coefficients show a peak near 1 GPa below T_C but a similar peak is also found near 1 GPa at 80 K, i.e., in the paramagnetic region. The compressibility shows an anomalous increase with decreasing temperature even in the paramagnetic region. These facts suggest that the paramagnetic state of UGe₂ is not only in the anomalous electronic state but also in the anomalous lattice state.