2024/02/19 by Zhengyan Darius Shi, Shi, Zhengyan Darius, Hart Goldman +5
Physics and Astronomy · Engineering · #Strong Light-Matter Interactions #Molecular Junctions and Nanostructures #Quantum and electron transport phenomena
paper · pdf · doi:10.48550/arxiv.2402.12436
We study a family of excitonic quantum phase transitions describing the evolution of a bilayer metallic state to an inter-layer coherent state where excitons condense. We argue that such transitions can be continuous and exhibit a non-Fermi liquid counterflow response ρcounterflow(ω)∼ω2/z that directly encodes the dynamical critical exponent z. Our calculations are performed within a controlled expansion around z = 2. This physics is relevant to any system with spin, valley, or layer degrees of freedom. We consider two contexts for excitonic quantum criticality: (1) a weakly interacting graphene bilayer, and (2) a system of two narrow, half-filled Chern bands at zero external magnetic field, with total Chern number Ctot=0, which may soon be realizable in moiré materials. The latter system hosts a time-reversed pair of composite Fermi liquid states, and the condensation of excitons of the composite fermions leads to an exotic exciton insulator* state with a charge neutral Fermi surface. Our work sheds new light on the physics of inter-layer coherence transitions in 2D materials.