Impact of domain disorder on optoelectronic properties of layered semimetal MoTe2

We address the impact of crystal phase disorder on the generation of helicity-dependent photocurrents in layered MoTe2, which is one of the van der Waals materials to realize the topological type-II Weyl semimetal phase. Using scanning photocurrent microscopy, we spatially probe the phase transition and its hysteresis between the centrosymmetric, monoclinic 1T’ phase to the symmetry-broken, orthorhombic Td phase as a function of temperature. We find a highly disordered photocurrent response in the intermediate temperature regime. Moreover, we demonstrate that helicity-dependent and ultrafast photocurrents in MoTe2 arise most likely from a local breaking of the electronic symmetries. Our results highlight the prospects of local domain morphologies and ultrafast relaxation dynamics on the optoelectronic properties of low-dimensional van der Waals circuits.

Phonon scattering and exciton localization: molding exciton flux in two dimensional disorder energy landscape

Two dimensional excitonic devices are of great potential to overcome the dilemma of response time and integration in current generation of electron or/and photon based systems. The ultrashort diffusion length of exciton arising from ultrafast relaxation and low carrier mobility greatly discounts the performance of excitonic devices. Phonon scattering and exciton localization are crucial to understand the modulation of exciton flux in two dimensional disorder energy landscape, which still remain elusive. Here, we report an optimized scheme for exciton diffusion and relaxation dominated by phonon scattering and disorder potentials in WSe2 monolayers. The effective diffusion coefficient is enhanced by > 200% at 280 K. The excitons tend to be localized by disorder potentials accompanied by the steadily weakening of phonon scattering when temperature drops to 260 K, and the onset of exciton localization brings forward as decreasing temperature. These findings identify that phonon scattering and disorder potentials are of great importance for long-range exciton diffusion and thermal management in exciton based systems, and lay a firm foundation for the development of functional excitonic devices.

Photo-Induced Coupled Nuclear and Electron Dynamics in the Nucleobase Uracil

Photo-initiated processes in molecules often involve complex situations where the induced dynamics is characterized by the interplay of nuclear and electronic degrees of freedom. The interaction of the molecule with an ultrashort laser pulse or the coupling at a conical intersection (CoIn) induces coherent electron dynamics which is subsequently modified by the nuclear motion. The nuclear dynamics typically leads to a fast electronic decoherence but also, depending on the system, enables the reappearance of the coherent electron dynamics. We study this situation for the photo-induced nuclear and electron dynamics in the nucleobase uracil. The simulations are performed with our ansatz for the coupled description of the nuclear and electron dynamics in molecular systems (NEMol). After photo-excitation uracil exhibits an ultrafast relaxation mechanism mediated by CoIn's. Both processes, the excitation by a laser pulse and the non-adiabatic relaxation, are explicitly simulated and the coherent electron dynamics is monitored using our quantum mechanical NEMol approach. The electronic coherence induced by the CoIn is observable for a long time scale due to the delocalized nature of the nuclear wavepacket.

Internal Conversion of the Anionic GFP Chromophore: In and Out of the I-twisted S1/S0 Conical Intersection Seam

<p>The functional diversity of the green fluorescent protein (GFP) family is intimately connected to the interplay between competing photo-induced transformations of the chromophore motif, anionic <i>p</i>-hydroxybenzylidene-2,3-dimethylimidazolinone (HBDI^–). Its propensity to undergo <i>Z/E</i> photoisomerization following excitation to the S₁(pp^*) state is of particular importance for super-resolution microscopy and emerging opportunities in optogenetics. However, key dynamical aspects of this process and its range of tunability still remain elusive. Here, we investigate the internal conversion behavior intrinsic to HBDI^– with focus on competing deactivation pathways, rate and yield of photoisomerization. Based on non-adiabatic dynamics simulations, we confirm that non-selective progress along the two bridge-torsional (i.e., phenolate, P, or imidazolinone, I) pathways can account for the three decay constants reported experimentally, leading to competing ultrafast relaxation along the I-twisted pathway and S₁trapping along the P-torsion. The majority of the population (~70%) is transferred to S₀ in the vicinity of two near-symmetry-related minima on the I-twisted intersection seam (MECI-Is). Despite their reactant-biased topographies, our account of inertial effects suggests that isomerization not only occurs as a thermal process on the vibrationally hot ground state but also as a direct photoreaction with a total quantum yield of ~40%.</p><p>By comparing the non-adiabatic dynamics to a photoisomerization committor analysis, we provide a detailed mapping of the intrinsic photoreactivity and dynamical behavior of the two MECI-Is. Our work offers new insight into the internal conversion process of HBDI^– that enlightens principles for the design of chromophore derivatives and protein variants with improved photoswitching properties.</p>

Internal Conversion of the Anionic GFP Chromophore: In and Out of the I-twisted S1/S0 Conical Intersection Seam

<p>The functional diversity of the green fluorescent protein (GFP) family is intimately connected to the interplay between competing photo-induced transformations of the chromophore motif, anionic <i>p</i>-hydroxybenzylidene-2,3-dimethylimidazolinone (HBDI^–). Its propensity to undergo <i>Z/E</i> photoisomerization following excitation to the S₁(pp^*) state is of particular importance for super-resolution microscopy and emerging opportunities in optogenetics. However, key dynamical aspects of this process and its range of tunability still remain elusive. Here, we investigate the internal conversion behavior intrinsic to HBDI^– with focus on competing deactivation pathways, rate and yield of photoisomerization. Based on non-adiabatic dynamics simulations, we confirm that non-selective progress along the two bridge-torsional (i.e., phenolate, P, or imidazolinone, I) pathways can account for the three decay constants reported experimentally, leading to competing ultrafast relaxation along the I-twisted pathway and S₁trapping along the P-torsion. The majority of the population (~70%) is transferred to S₀ in the vicinity of two near-symmetry-related minima on the I-twisted intersection seam (MECI-Is). Despite their reactant-biased topographies, our account of inertial effects suggests that isomerization not only occurs as a thermal process on the vibrationally hot ground state but also as a direct photoreaction with a total quantum yield of ~40%.</p><p>By comparing the non-adiabatic dynamics to a photoisomerization committor analysis, we provide a detailed mapping of the intrinsic photoreactivity and dynamical behavior of the two MECI-Is. Our work offers new insight into the internal conversion process of HBDI^– that enlightens principles for the design of chromophore derivatives and protein variants with improved photoswitching properties.</p>