Quantum Geometric Dipole in Collective Excitations

In recent years it has become increasingly appreciated that electrons in solids possess quantum geometric structure that impact the electronic properties of the system.  Typically, this takes the form of a Berry curvature which contributes to the electron velocity in its response to external fields.  In this talk we discuss quantum geometric properties of collective modes of electronic materials, focusing on those that can be described as two-body excitations.  We show that generally such excitations possess their own type of geometric measure, closely related to an electric dipole moment, which we call the quantum geometric dipole (QGD).  We will focus on two examples of this: excitons in semiconducting systems, and plasmons in two-dimensional metals.  We show that for excitons, a non-zero QGD appears when there is no effective Lorentz invariance in the system, even at long wavelengths, and that its presence leads to a perpendicular exciton drift in an electric field.  For the case of plasmons, we consider the impact of the QGD on scattering from a circularly symmetric potential, showing that the QGD necessarily gives rise to non-reciprocal behavior.  In general the presence of a non-vanishing QGD impacts the dynamics of these collective modes, and we discuss some implications for experiment.

Hosts: Fernando de Juan

Auditorium, Centro de Fisica de Materiales


Herbert Abraham Fertig, Indiana University

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