Dynamic theory of nanophotonic control of two-dimensional semiconductor nonlinearities

Abstract

We introduce a Maxwell-Bloch simulation approach which self-consistently combines a microscopic description of the carrier and polarisation dynamics of a transition-metal-dichalcogenide (TMDC) monolayer with a spatio-temporal full-wave time-domain simulation of Maxwell's equations on the basis of a finite-difference time-domain (FDTD) method beyond the slowly-varying amplitude or paraxial approximations. This offers a platform to realistically model, in particular, the typical ultrafast optical excitation experiments in micro-and nanocavities. Our simulations confirm that the weak screening of the Coulomb interaction in TMDC monolayers yields pronounced exciton lines in the linear spectrum and we uncover the second order nonlinearity represented in the semiconductor Maxwell-Bloch equations by an intraband dipole moment. This allows us to calculate the spectral shape of the exceptionally strong second harmonic generation around the exciton lines of TMDC monolayers. We demonstrate that the second harmonic signal can remarkably be further enhanced by several orders of magnitude through a suitably designed (one-dimensional) photonic microcavity. Due to its self-consistency, flexibility, explicit spatio-temporal resolution on the nanoscale and the ready access to light field and electron dynamics, our theory and computational approach is an ideal platform to design and explore spatio-temporal nonlinear and quantum dynamics in complex photonic or plasmonic micro-and nano-structures for opto-electronic, nanophotonic and quantum applications of TMDC monolayers.

Preserving the Emission Lifetime and Efficiency of a Monolayer Semiconductor upon Transfer

“…We plot the normalized time‐resolved PL decay measurements of monolayer WS 2 , obtained via FLIM, before and after soft‐transfer encapsulation in these dielectric substrates in Figure S3 (Supporting Information). In Table 1 , we summarize the static dielectric constants (ε 0 ) and the dielectric constant at optical frequencies (ε ∞ ) of each substrate, as well as the emission decay parameters of the monolayers before and after transfer, considering that both ε 0 and ε ∞ can affect the electric (i.e., dielectric screening) and optical properties of the excitons, respectively.…”

“…In structures such as microcavities or metal nanoantennas, dielectric layers are frequently placed on top of the TMD monolayer to tune optical resonances, to protect the samples from degradation, or as spacers to avoid charge transfer. In this way, TMD monolayers may be surrounded by a dielectric environment that could modify their absorption and emission, which if controllable, is desirable for engineering properties such as the optical density of states or dielectric screening . Furthermore, variations in fabrication methods and processing techniques of these configurations can also lead to the uncontrolled modification in emission efficiency and photoluminescence (PL) lifetime of the monolayers .…”

Effective detection of spatio-temporal carrier dynamics by carrier capture

“…As a testbed, we will consider the diffraction of an electronic wave packet moving in a monolayer of a transition metal dichalcogenide (TMDC) at an obstacle. TMDCs represent a class of 2D semiconducting materials which has recently attracted lots of attention [32][33][34][35][36][37][38], mostly due to their excitonic properties, although a mixture of bound and unbound electron-hole pairs could be present [39,40]. In these materials QDs can be created efficiently, e.g.…”