Electrons in quantum materials reside on a crystal lattice, making the application of lattice strains a very powerful tuning parameter to induce and control a range of exciting quantum phenomena. Recent experimental advances have allowed the application of very large strains with different symmetry properties, such as symmetry-breaking uniaxial pressures and symmetry-preserving hydrostatic pressures. In this talk, I will show specific studies on correlated and topological magnets, highlighting how the different types of strains provide unique insights into the underlying physics.

First, I will discuss how the symmetry-breaking nature of uniaxial pressure can critically modify heavy-fermion materials and frustrated magnets. I will show that the novel method of elastocaloric effect measurements is highly suited to map out their phase diagrams as a function of strain. Importantly, I will show how these experiments can reveal the location of entropy extrema, such as those associated with maximum frustration, in the temperature-strain phase diagram.

Second, I will discuss the tuning of the magnetic state in a proposed Weyl semimetal EuCd 2 As 2 . By applying hydrostatic pressures, i.e. volumetric, symmetry-conserving strains, we induce a phase transition to a ferromagnetic phase, which is predicted to host the Weyl fermions. I will emphasize that preserving the lattice symmetry is fundamental to the stabilization of the putative Weyl phase.

References
1. E. Gati et al., Annalen der Physik, 2000248 (2020); N.H. Jo et al., submitted (2024) (invited review articles)
2. E. Gati et al., npj Quant. Mat. 8, 69 (2023).
3. E. Gati et al., Phys. Rev. B 104, 155124 (2021).