Very few materials are able to absorb visible light without dissipating some of the resulting energy into phonon modes, and these excited modes have the capability to act back on the electronic excitation that is generated. By the same token, very few probes of photophysical processes in materials are able to directly probe the coexistence of both electronic and thermal departures from equilibrium or directly visualize the impact of the spatiotemporal interaction of electronic and thermal excitations. I will nevertheless, describe such a capability that leverages not only the ps time resolution associated with electronic to thermal energy transduction but that also provides direct spatial maps of localized photoinduced electronic and temperature profiles and their coupled evolution. I will how how this approach allows us to investigate thermoelectric effects in few-layer MoS_2 and that it can be more broadly applied to other emerging semiconductors.
Non-hydrogenic Rydberg series associated with excitons have been identified in ultraclean monolayer TMDCs. Here, we investigated the radiative properties of the excitonic Rydberg series in monolayer MoTe2 based devices and the influence of Fermi level position on the same. Using low temperature (4K) photoluminescence measurements, we observed bright emission from the first three states of the excitonic Rydberg series, namely A1s, 2s and 3s. Upon doping on either electron or hole side, oscillator strengths are rapidly transferred to the corresponding trion (charged exciton/attractive polaron) states associated with the aforementioned neutral excitonic resonances. Energy shifts between different states are observed as a function of gate voltage, indicating strong band-structure renormalization. Our work identifies MoTe2 as a novel platform to realize highly tunable bright light sources or electro-optic modulators in the NIR.
Characterizing the intrinsic properties of low-dimensional transition metal dichalcogenides (TMDCs) is necessary for explaining how their novel properties arise and are modified by their local environment. Excitations in few-layer TMDCs and heterostructures are difficult to probe directly because of their low photoluminescence quantum yield. With time-resolved elastic scattering microscopy, we spatiotemporally resolve both in-plane and out-of-plane nanoscale transport in several TMDC species and architectures as a function of layer thickness and pump-induced carrier density. We directly observe interlayer exciton transport in TMDC heterostructures and find that these species diffuse an order of magnitude farther and faster than excitations do in their isolated counterparts.
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