Research: High-precision control of crystal-electric field levels by strain tuning in a heavy fermion

Quantum materials are characterized by several competing energy scales, which are responsible for their exotic behaviour. High-precision tuning of these energy scales is a key challenge in quantum materials research in order to control their emergent phenomena.

In the context of correlated magnetism, the energy scales associated with the crystal electric field levels play a crucial role in determining the interactions between the spins. In this paper, we report a novel method to control and probe changes in the crystal electric field scheme by uniaxial pressure tuning. Uniaxial pressure and strain are highly effective control parameters because of their ability to break the underlying lattice symmetries. We explicitly demonstrate this experimentally in a cubic heavy fermion system, YbPtBi, where the Kramers-degenerate quartet is susceptible to splitting by symmetry-breaking uniaxial pressure. By measuring the elastocaloric effect - i.e., the temperature induced by a change in strain - and comparing it with model calculations, we explicitly quantify the change in crystal electric field levels with strain. This new approach will be highly relevant for the study of frustrated magnets and other quantum materials under strain.

E. Gati, B. Schmidt, S. L. Bud'ko, A. P. Mackanzie, P. C. Canfield,
Elastocaloric effect of the heavy-fermion system YbPtBi,
npj Quantum Materials 8, 69 (2023) (arXiv)