Enhancement in optically induced ultrafast THz response of MoSe2MoS2 heterobilayer

TL;DR

This study investigates the enhanced ultrafast THz response of MoSe2/MoS2 heterobilayers, revealing significant reflectivity increases upon optical excitation, with insights into the underlying mechanisms.

Contribution

It presents the first detailed measurement of THz conductivity in MoSe2/MoS2 heterobilayers and uncovers unexpected enhancements below the bandgap energies.

Findings

Ultrafast THz reflectivity is significantly enhanced in heterobilayers.

Enhancement occurs even when excited below the monolayers' bandgaps.

A proposed mechanism explains these observations.

Abstract

THz conductivity of large area MoS2 and MoSe2 monolayers as well as their vertical heterostructure, MoSe2MoS2 is measured in the 0.3-5 THz frequency range. Compared to the monolayers, the ultrafast THz reflectivity of the MoSe2MoS2 heterobilayer is enhanced many folds when optically excited above the direct band gap energies of the constituting monolayers. The free carriers generated in the heterobilayer evolve with the characteristic times found in each of the two monolayers. Surprisingly, the same enhancement is recorded in the ultrafst THz reflectivity of the heterobilayer when excited below the MoS2 bandgap energy. A mechanism accounting for these observations is proposed.