Pressure-induced valence transition and characteristic electronic states in EuRh₂Si₂

EuRh₂Si₂ is well known to show a valence transition at a pressure of about 1 GPa from a Eu-divalent (antiferromagnetic) state to a nearly Eu-trivalent (paramagnetic) state, which was clarified using polycrystalline samples. We have succeeded in growing single crystals of EuRh₂Si₂ by the Bridgman method and studied their electronic properties measuring the electrical resistivity under pressure. EuRh₂Si₂ indicates a first-order valence transition in the pressure range from 1 to 2 GPa, distinguished by a sharp transition and a prominent hysteresis in the temperature dependence of the electrical resistivity. A critical end point in the valence transition is estimated as P_CEP ≃ 2.05 GPa and T_CEP ≃ 170 K. In the pressure range from 2 to 3 GPa, the electrical resistivity is found to exhibit a characteristic behavior for a moderately heavy-fermion compound such as EuIr₂Si₂. At pressures higher than 3 GPa, the resistivity reveals a normal metallic behavior in a nearly trivalent electronic state. This is the first report on the pressure evolution of the electronic states from the antiferromagnetically ordered state to the moderate heavy-fermion state and nearly trivalent state, via the first-order valence transition.