In single-layer semiconducting transition metal dichalcogenides (TMDs), strong quantum confinement and reduced dielectric screening, due to their two-dimensional structure, leads to tightly bound excitons, trions and higher-order bound states. Understanding the temporal evolution of such complexes after optical excitation and their response to external stimuli is essential for unlocking their potential in optoelectronic applications. First, we investigate the influence of electrostatic doping via the field-eƯect on the ultrafast dynamics of trions in single layer TMDs using broadband femtosecond pump-probe microscopy. We study the temporal dynamics of excitons and trions as the primary photoexcited species, disentangle the formation of trions from photogenerated vs electrostatically injected charge carriers and discuss the formation of neutral and charged biexcitons.
As a second control parameter, we investigate the role of strain, which influences the whose resonant energy, eƯective mass, and mobility of excitons and carriers. We report the modulation of the exciton recombination in monolayer WS2 via the application of uniaxial tensile strain. For 1 % applied strain the dominant (few-ps-1) recombination rate increases over the unstrained case by a factor of two. We ascribe these fast dynamics to the exciton migration towards ultrafast recombination centers and the strain-induced enhancement of this process to an increased exciton diƯusion. Coherent excitation of phonons with suƯiciently short laser pulses leads to a periodic strain modulation of optical spectra. In monolayer MoTe2 we observe a dramatic rearrangement of the optical absorption induced by an out-of-plane stretching and compression of the crystal lattice, consistent with displacive excitation of an A1g -type oscillation.
In single-layer semiconducting transition metal dichalcogenides (TMDs), strong quantum confinement and reduced dielectric screening, due to their two-dimensional structure, leads to tightly bound excitons, trions and higher-order bound states. Understanding the temporal evolution of such complexes after optical excitation and their response to external stimuli is essential for unlocking their potential in optoelectronic applications. First, we investigate the influence of electrostatic doping via the field-eƯect on the ultrafast dynamics of trions in single layer TMDs using broadband femtosecond pump-probe microscopy. We study the temporal dynamics of excitons and trions as the primary photoexcited species, disentangle the formation of trions from photogenerated vs electrostatically injected charge carriers and discuss the formation of neutral and charged biexcitons.
As a second control parameter, we investigate the role of strain, which influences the whose resonant energy, eƯective mass, and mobility of excitons and carriers. We report the modulation of the exciton recombination in monolayer WS2 via the application of uniaxial tensile strain. For 1 % applied strain the dominant (few-ps-1) recombination rate increases over the unstrained case by a factor of two. We ascribe these fast dynamics to the exciton migration towards ultrafast recombination centers and the strain-induced enhancement of this process to an increased exciton diƯusion. Coherent excitation of phonons with suƯiciently short laser pulses leads to a periodic strain modulation of optical spectra. In monolayer MoTe2 we observe a dramatic rearrangement of the optical absorption induced by an out-of-plane stretching and compression of the crystal lattice, consistent with displacive excitation of an A1g -type oscillation.
