Ultrafast Optical Probing of Correlated Polar Metals
There is considerable interest today in quantum materials. While all materials obey quantum mechanics, there is specific interest in phenomena that go beyond the independent single electron approximation, and arise in strongly correlated electron systems, strong spin-orbit coupled systems, and topologically protected systems. In this talk, I will present an interesting state of matter called polar metals in a correlated electron system, Ca3Ru2O7. The talk will present the origin of the counterintuitive polar displacements in a bulk metal, and show that it has domains and domain walls, much like an insulating ferroelectric. The walls have built in electrical potential of tens of meV, on the order of switching voltages for a modern-day transistor of 60 meV/decade. By using low fluence ultrafast optics, one can gently perturb the Fermi surface and study ultrafast dynamics of quasiparticles. Of the two metal insulator transitions, seen in this system, the 30K transition is still a mystery; we reveal that it is not a true transition, but a crossover related to the evolution of a pseudogap competing with a drop in the carrier scattering rate upon cooling. A rich range of electron structure, transport properties and thermodynamic parameters are extracted from such an optical study.