Probing giant elastic coupling in exotic magnets and superconductors
What holds a solid together? Obviously it is bonding between electrons, but which ones? There is plenty of evidence that electrons in energy bands below the Fermi level play a key role – for example, the lattice stiffnesses of most insulators and most metals are similar. From a physicist’s perspective, these so-called valence electrons determine the characteristics of the lattice through which the conduction electrons at the Fermi level flow. However, that is not the whole truth. Remarkably, in some special situations, the conduction electrons can be tuned to make the lattice much softer, resulting in states in which the elastic and electronic degrees of freedom are strongly entangled [1, 2]. Many magnetic systems, both conducting and insulating, also feature strong magneto-elastic coupling with the potential to generate new physics.
![Giant elastic coupling between conduction electrons and the lattice in Sr2RuO4 (left panel, from [1]) and in an organic conductor (right panel, from [2]). In both materials, the regime of strong entanglement between elastic and electronic degrees of freedom is accessed by applying pressure to the sample. In Sr2RuO4, uniaxial pressure tunes the Fermi level to a Van Hove singularity; in the organic conductor, hydrostatic pressure tunes the material through a Mott insulator-metal transition.](/190866/original-1695638380.jpg?t=eyJ3aWR0aCI6ODQ4LCJmaWxlX2V4dGVuc2lvbiI6ImpwZyIsIm9ial9pZCI6MTkwODY2fQ%3D%3D--14d13c3c8c8eb3a4ca6cd944608f7246da8dd463 "Giant elastic coupling between conduction electrons and the lattice in Sr2RuO4 (left panel, from [1]) and in an organic conductor (right panel, from [2]). In both materials, the regime of strong entanglement between elastic and electronic degrees of freedom is accessed by applying pressure to the sample. In Sr2RuO4, uniaxial pressure tunes the Fermi level to a Van Hove singularity; in the organic conductor, hydrostatic pressure tunes the material through a Mott insulator-metal transition.")
![Giant elastic coupling between conduction electrons and the lattice in Sr2RuO4 (left panel, from [1]) and in an organic conductor (right panel, from [2]). In both materials, the regime of strong entanglement between elastic and electronic degrees of freedom is accessed by applying pressure to the sample. In Sr2RuO4, uniaxial pressure tunes the Fermi level to a Van Hove singularity; in the organic conductor, hydrostatic pressure tunes the material through a Mott insulator-metal transition.](/190866/original-1695638380.jpg?t=eyJ3aWR0aCI6MjQ2LCJvYmpfaWQiOjE5MDg2Nn0%3D--759bbc46ae0c7163bb3f47d42c4f54815d830313)
Thanks to some of the unique apparatus developed over the last decade in our department, we have the capability of making precise measurements of the lattice stiffness while we use uniaxial pressure to tune the lattice parameters. It is possible to tune the position of the Fermi level in metals and the magnetic exchange in magnetic systems. This exciting new capability will give us access to a wealth of new many-body states. Unconventional superconductivity and exotic magnetic states such as spin liquids are obvious targets for the research; the techniques we will employ are sufficiently novel that careful experiments may also lead to discovery of things we have not yet imagined!
We are able to offer more than one project in this general field of research.
