Exciton migration in two-dimensional materials

TL;DR

This paper demonstrates how ultrashort UV pulses can induce and control exciton migration in two-dimensional materials like hBN, using real-time simulations and ultrafast spectroscopy to explore electron coherence and valley dynamics.

Contribution

It introduces a novel method to induce and measure exciton migration in 2D materials using ultrafast pulses and spectroscopy, advancing ultrafast electronics and valleytronics.

Findings

Ultrashort UV pulses create coherent superpositions of excitonic states.

Exciton migration can be observed as oscillatory electron-hole motion.

Ultrafast spectroscopy can measure the characteristic time of exciton migration.

Abstract

Excitons play an essential role in the optical response of two-dimensional materials. These are bound states showing up in the band gaps of many-body systems and are conceived as quasiparticles formed by an electron and a hole. By performing real-time simulations in hBN, we show that an ultrashort (few-fs) UV pulse can produce a coherent superposition of excitonic states that induces an oscillatory motion of electrons and holes between different valleys in reciprocal space, leading to a sizeable exciton migration in real space. We also show that an ultrafast spectroscopy scheme based on the absorption of an attosecond pulse in combination with the UV pulse can be used to read out the laser-induced coherences, hence to extract the characteristic time for exciton migration. This work opens the door towards ultrafast electronics and valleytronics adding time as a control knob and exploiting electron coherence at the early times of excitation.