Dr. Mengxing Ye, UC, Santa Barbara

"New ideas to probe exotic phases in quantum materials"

Abstract: With the advancements in quantum materials research, the emergent quantum many-body phases that exhibit competing orders, topological order and/or fractionalization, can be realized in much more controllable ways, by e.g. heterostructuring, ultraclean novel materials synthesis and ultrafast laser control. However, resolving them experimentally can be challenging. For example, understanding experiments carried out at finite temperature in systems with disorder requires careful evaluations of the interplay between quantum and thermal fluctuations as well as randomness. As another example, in phases with fractionalized excitations, understanding the signatures through conventional probes requires a careful study on the correlation of the composite of the fractionalized excitations.

In this talk, I will discuss new ideas to probe these exotic phases, with setups both in and out of equilibrium. First, I will discuss our theory of the charge orders in recently extensively studied Vanadium based kagomé metals, which show a cascade of phase transitions as temperature lowers, from charge order, potential time reversal symmetry breaking order to superconductivity. The constraints on the theory space that are consistent with various experiments will be elaborated. Second, I will introduce our theory of metal-insulator-transition with charge fractionalization. Its implications to understand a recent transport experiment on transition metal dichalcogenide moiré heterostructures and other predictions at and near the transition will be discussed. And third, I propose the use of ultrafast pump-probe setup to study the time-domain dynamics of (quasi) long range order in two dimensional magnets, which in the meantime can reveal the interactions between low and high energy states of the system. I will conclude with an outlook on further developing these ideas to probe other exotic quantum many-body phases.