under pressure*

Antiferromagnetic CeRhIn₅ is a prototypical heavy-fermion compound. With applied pressure, the antiferromagnetic ordering of CeRhIn₅ disappears and an unconventional superconducting state emerges. Crystalline electric field (CEF) effects are known to be important in the determination of the ground state of heavy-fermion materials. However, CEF effects in CeRhIn₅ have not been studied under pressure because of the limiting volume and background of pressure cells. Here we probe the CEF scheme of CeRhIn₅ via thermal expansion measurements under pressure using the strain gauge method at high temperature and optical fiber sensors at low temperature. We report the temperature dependence of the linear thermal-expansion coefficient of CeRhIn₅ under pressure. Our results allow us to determine CEF splitting energies from the ground state to the excited state and observe the evolution of the phase transitions under pressure. We will discuss the pressure dependence of CEF effects in CeRhIn₅ in comparison with other 115 compounds.