Epitaxial Stabilization of an Unconventional Oxide Superconductor

Complex oxides are a fascinating class of quantum materials, displaying almost every physical ground state known. To date, much of the work has focused on the perovskite oxides, including the well-studied cuprate superconductors as well as the more recently discovered nickelate superconductors. In my talk, I will discuss a different class of oxide quantum materials, the geometrically frustrated spinel-based materials. Geometrically frustrated lattices can display a range of correlated phenomena, ranging from spin frustration and charge order to dispersionless flat bands due to quantum interference. One particularly compelling family of such materials is the half-valence spinel LiB2O4 materials. On the B-site frustrated pyrochlore sublattice, the interplay of correlated metallic behavior and charge frustration leads to a superconducting state in LiTi2O4 and heavy fermion behavior in LiV2O4. To date, however, LiTi2O4 has primarily been understood as a conventional BCS superconductor despite a lattice structure that could host more exotic ground states. I will present a multimodal investigation of LiTi2O4, combining ARPES, RIXS, proximate magnetic probes, and ab-initio many-body theoretical calculations. Our data reveals a novel mobile polaronic ground state displaying spectroscopic signatures of co-dominant electron-phonon coupling and electron-electron correlations. I will conclude by putting this material in the context of other unconventional superconductors.