Anisotropic Elastic Properties of CeRhIn₅

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The structure of the quasi two dimensional heavy fermion antiferromagnet CeRhIn₅ has been investigated as a function of pressure up to 13 GPa using a diamond anvil cell under both hydrostatic and quasihydrostatic conditions at room (T=295 K) and low (T=10 K) temperatures. Complementary resonant ultrasound measurements were performed to obtain the complete elastic moduli. The bulk modulus (B≈ 78 GPa) and uniaxial compressibilities (κₐ =3.96× 10⁻³ GPa⁻¹ and % κc =4.22× 10⁻³ GPa⁻¹) found from pressure-dependent x-ray diffraction are in good agreement with the ultrasound measurements. Unlike doping on the Rh site where Tc increases linearly with the ratio of the tetragonal lattice parameters c/a, no such correlation is observed under pressure; instead, a double peaked structure with a local minimum around 4-5 GPa is observed at both room and low temperatures.