Rich Harmonic Generation from Exciton Bloch Oscillations

Collective modes of electron systems can support novel quantum geometric and topological properties due to their internal structure. Among these, interlayer excitons in two-dimensional systems support an unusual "quantum geometric dipole" (QGD) that is determined by its momentum [1]. In this work we discuss the evolution of the QGD as it moves through the Brillouin zone of a periodic potential. As a concrete example, we consider interlayer magneto-excitons in a one-dimensional potential, driven by an antisymmetric in-plane electric field. The resulting Bloch oscillations yield an oscillating electric dipole moment which, in a single-band approximation, hosts a remarkably rich harmonic spectrum. We discuss the radiative power generated by such excitons, as well as the degrading effects of interband tunneling and scattering, and consider the potential of this system to produce radiation with very high harmonics of the Bloch oscillation frequency.