Probing Electron-Hole Coherence in Strongly-Driven Solids

TL;DR

This paper demonstrates a novel method to measure electron-hole coherence in strongly driven solids by analyzing high-harmonic generation suppression, revealing ultrafast dephasing effects and many-body interactions in monolayer molybdenum disulfide.

Contribution

It introduces a new approach to probe electron-hole coherence using HHG suppression in photo-doped monolayer MoS2, highlighting many-body dephasing effects.

Findings

HHG intensity suppression increases with harmonic order

Ultrafast electron-hole dephasing causes exponential decay of inter-band polarization

Many-body effects influence HHG efficiency in strongly driven systems

Abstract

High-harmonic generation (HHG) is a coherent optical process in which the incident photon energy is up-converted to the multiples of its initial energy. In solids, under the influence of a strong laser field, electron-hole (e-h) pairs are generated and subsequently driven to high energy and momentum within a fraction of the optical cycle. These dynamics encode the band structure, including non-trivial topological properties of the source material, through both intraband current and interband polarization, into the high harmonic spectrum. In the course of this process, dephasing between the driven electron and the hole can significantly reduce the HHG efficiency. Here, we exploit this feature and turn it into a measurement of e-h coherence in strongly driven solids. Utilizing a pre-pump pulse, we first photodope monolayer molybdenum disulfide and then examine the HHG induced by an intense infrared pulse. We observe clear suppression of the HH intensity, which becomes more pronounced with increasing order. Based on quantum simulations, we attribute this monotonic order dependence as a signature of ultrafast electron-hole dephasing, which leads to an exponential decay of the inter-band polarization, proportional to the sub-cycle excursion time of the e-h pair. Our results demonstrate the importance of many-body effects, such as density-dependent decoherence in HHG and provide a novel platform to probe electron-hole coherence in strongly driven systems.