Professor Herb Fertig

Department of Physics

Indiana University

Host: Kaul

Title:

Exciton Drift from Quantum Geometry

Abstract:

In some situations, excitons – bound particle-hole pairs above an insulating ground state – carry an electric dipole moment, allowing them to be manipulated via coupling to an electric field. Excitons in two-dimensional systems turn out to be fully determined by the quantum geometry of its eigenstates, through a quantity which we call the dipole curvature.  The dipole curvature arises naturally in the semiclassical equations of motion of an exciton in an electric field, yielding a drift velocity akin to that expected for excitons in crossed electric and magnetic fields, even in the absence of a real magnetic field.  In real magnetic fields it yields corrections to the drift velocity expected based on Lorentz invariance.  The effect arises naturally in systems where the environments of the electron and hole are sufficiently different, and is particularly relevant for interlayer excitons in heterostructures -- bilayers of different materials.  We discuss estimates of these effects for simple heterostructure models, including graphene and transition-metal dichalcogenide layers, both with and without magnetic fields.  The last of these turn out to be particularly promising platforms for observing these effects.   We discuss how this quantum geometric drift velocity might be observed in experiment, and possible further consequences that follow from the semiclassical dynamics.