Nonlinear exciton drift in piezoelectric two-dimensional materials

TL;DR

This paper models nonlinear exciton transport in 2D transition metal dichalcogenides, revealing a piezoelectric effect-induced dipole interaction that leads to unique exciton droplet formations, tunable by nano-bubble geometry.

Contribution

It introduces a microscopic model of nonlinear exciton transport driven by giant piezoelectric fields in 2D materials, highlighting a novel dipole-dipole interaction mechanism.

Findings

Giant piezoelectric fields induce significant internal electric fields.

Nonlinear exciton transport leads to hexagon-shaped exciton droplets.

The effect is tunable via nano-bubble size parameters.

Abstract

Noncentrosymmetric nature of single-layer transition metal dichalcogenides manifest itself in the finite piezoelectricity and valley-Zeeman coupling. We microscopically model nonlinear exciton transport in nano-bubble of single-layers of transition metal dichalcogenide. Thanks to the giant piezoelectric effect, we obtain an enormous internal electric field, $E_{\rm piezo}\sim 10^7$V/m, resulting in a built-in dipole moment of excitons. We demonstrate that the piezo-induced dipole-dipole interaction provides a novel channel for the nonlinear exciton transport distinct from the conventional isotropic funneling of excitons and leading to the formation of hexagon-shaped exciton droplet on top of a circularly symmetric nano-bubble. The effect is tunable via the bubble size dependence of the piezo-electric field $E_{\rm piezo} \sim h^2_{\rm max}/R^3$ with $h_{\rm max}$ and $R$ being the bubble height and radius, respectively.