Electrical Resistivity and Thermal Expansion Measurements of URu2Si2 under Pressure

TL;DR

This study investigates how electrical resistivity and thermal expansion in URu2Si2 change under pressure, revealing distinct phase transition anomalies and pressure-dependent excitation gaps between hidden and antiferromagnetic states.

Contribution

It provides new insights into the pressure dependence of phase transitions and excitation gaps in URu2Si2 using simultaneous resistivity and thermal expansion measurements.

Findings

Distinct anomalies at phase transition temperatures T0 and TM.

Different pressure dependences of excitation gaps Delta_HO and Delta_AFM.

No critical end point; phase boundaries meet at a critical point.

Abstract

We carried out simultaneous measurements of electrical resistivity and thermal expansion of the heavy-fermion compound URu2Si2 under pressure using a single crystal. We observed a phase transition anomaly between hidden (HO) and antiferromagnetic (AFM) ordered states at TM in the temperature dependence of both measurements. For the electrical resistivity, the anomaly at TM was very small compared with the distinct hump anomaly at the phase transition temperature T0 between the paramagnetic state (PM) and HO, and exhibited only a slight increase and decrease for the I // a-axis and c-axis, respectively. We estimated each excitation gap of HO, Delta_HO, and AFM, Delta_AFM, from the temperature dependence of electrical resistivity; Delta_HO and Delta_AFM have different pressure dependences from each other. On the other hand, the temperature dependence of thermal expansion exhibited a small anomaly at T0 and a large anomaly at TM. The pressure dependence of the phase boundaries of T0 and TM indicates that there is no critical end point and the two phase boundaries meet at the critical point.