Elastocaloric investigation of the response of the heavy fermion CePd₂Si₂ to anisotropic strain

Utilizing the adiabatic elastocaloric effect we study the response of the heavy fermion material CePd₂Si₂ to anisotropic strain. We focus on two specific aspects: first the effect of anisotropic strains on the antiferromagnetic phase transition, and second on obtaining direct measurements of the anisotropic Gruneisen ratios associated separately with in-plane and c-axis strains. We note that elastocaloric effect measurements offer a direct probe of various Gruneissen ratios, providing a much higher fidelity measurement than obtained by taking the ratio of thermal expansion and heat capacity. We apply uniaxial stress in three distinct, high-symmetry orientations (along [001], [100], and [110]) to obtain symmetry-resolved information. The AC strain is applied at a given frequency and temperature oscillations are measured using a RuOx sensor. We find that antisymmetric strains have negligible effect relative to the symmetry-conserving in-plane and c-axis strains on both the antiferromagnetic phase transition and the Gruneissen ratio. Notably, we find that in-plane compression suppresses the antiferromagnetic phase two orders of magnitude more effectively than c-axis compression; meanwhile, the Gruneisen ratio in the paramagnetic phase differs by less than a factor of two between in-plane and out-of-plane channels. These results provide experimental support for a possible quasi-two dimensionality of the antiferromagnetic order and the isotropic nature of the Kondo interactions in CePd₂Si₂ and highlight the elastocaloric effect as a powerful symmetry-resolving probe for heavy fermion metals.