EQuAL Student Seminar: Sarah Schwarz
3D Charge Density Wave in Superconducting Laves Phase Metal
Quantum materials with electronic flat-bands created by geometric hop ping interference (kinetic frustration) are an exciting field of research to explore materials with unusual and potentially useful electronic behavior. Examples include predictions of high temperature quantum anomalous Hall effects and numerous other nonperturbative states born from the interplay between correlation effects and nontrivial topology. Flat band states of this nature are guaranteed to form within crystal lattice structures which are line graphs of another lattice type. One lattice geometry known to produce these flat bands is the two-dimensional kagome network (network of corner sharing triangles), which is a line-graph lattice of the honeycomb structure. However, a complication for this network arises in real materials - there are inevitably interplane hopping terms operative which impart dispersion to the naively flat band states. An alternative is to instead explore three-dimensional flat band states that predicted in pyrochlore networks, which are line graphs of the diamond lattice. The pyrochlore lattice can alternatively be visualized as three intersecting kagome planes, and recent experiments have demonstrated that three-dimensional flat bands indeed form within pyrochlore metals. One exciting variant within this class of metals is the compound ZrV2. ZrV2 is a C15 Laves phase compound with a superconducting ground state (Tc≈8K). We have succeeded in growing high purity, bulk single crystals of this system for the first time using traveling solvent, floating zone techniques. Curiously, our recent x-ray scattering measurements of optimized crystals have discovered an unusual charge density wave (CDW) state that seemingly competes with a low temperature order parameter or exhibits reentrance at low-T. This is a highly unusual example of a three-dimensional CDW superconductor, and the connection of this behavior to potential flat band effects is a topic of ongoing study.
