The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
B Urbaszek - One of the best experts on this subject based on the ideXlab platform.
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exciton radiative lifetime in transition metal dichalcogenide monolayers
Physical Review B, 2016Co-Authors: Cedric Robert, Gang Wang, D Lagarde, F Cadiz, Benjamin Lassagne, T Amand, Andrea Balocchi, P Renucci, Sefaattin Tongay, B UrbaszekAbstract:©2016 American Physical Society. We have investigated the exciton dynamics in transition metal dichalcogenide monolayers using time-resolved photoluminescence experiments performed with optimized time resolution. For MoSe2 monolayer, we measure τrad0=1.8±0.2ps at T=7K that we interpret as the intrinsic radiative recombination time. Similar values are found for WSe2 monolayers. Our detailed analysis suggests the following scenario: at low temperature (T<50K), the exciton oscillator strength is so large that the entire light can be emitted before the time required for the establishment of a thermalized exciton distribution. For higher lattice temperatures, the photoluminescence dynamics is characterized by two regimes with very different characteristic times. First the photoluminescence intensity drops drastically with a decay time in the range of the picosecond driven by the escape of excitons from the radiative window due to exciton-phonon interactions. Following this first nonthermal regime, a thermalized exciton population is established gradually yielding longer photoluminescence decay times in the nanosecond range. Both the exciton effective radiative recombination and nonradiative recombination channels including exciton-exciton annihilation control the latter. Finally the temperature dependence of the measured exciton and trion dynamics indicates that the two populations are not in thermodynamical equilibrium.
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exciton radiative lifetime in transition metal dichalcogenide monolayers
Physical Review B, 2016Co-Authors: Cedric Robert, Gang Wang, D Lagarde, F Cadiz, Benjamin Lassagne, T Amand, Andrea Balocchi, P Renucci, Sefaattin Tongay, B UrbaszekAbstract:We have investigated the exciton dynamics in transition metal dichalcogenide monolayers using time-resolved photoluminescence experiments performed with optimized time resolution. For $\mathrm{MoS}{\mathrm{e}}_{2}$ monolayer, we measure ${\ensuremath{\tau}}_{\mathrm{rad}}^{0}=1.8\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{0.16em}{0ex}}\mathrm{ps}$ at $T=7\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ that we interpret as the intrinsic radiative recombination time. Similar values are found for $\mathrm{WS}{\mathrm{e}}_{2}$ monolayers. Our detailed analysis suggests the following scenario: at low temperature $(T\ensuremath{\lesssim}50\phantom{\rule{0.16em}{0ex}}\mathrm{K})$, the exciton oscillator strength is so large that the entire light can be emitted before the time required for the establishment of a thermalized exciton distribution. For higher lattice temperatures, the photoluminescence dynamics is characterized by two regimes with very different characteristic times. First the photoluminescence intensity drops drastically with a decay time in the range of the picosecond driven by the escape of excitons from the radiative window due to exciton-phonon interactions. Following this first nonthermal regime, a thermalized exciton population is established gradually yielding longer photoluminescence decay times in the nanosecond range. Both the exciton effective radiative recombination and nonradiative recombination channels including exciton-exciton annihilation control the latter. Finally the temperature dependence of the measured exciton and trion dynamics indicates that the two populations are not in thermodynamical equilibrium.
Libai Huang - One of the best experts on this subject based on the ideXlab platform.
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twist angle dependent interlayer exciton diffusion in ws 2 wse 2 heterobilayers
Nature Materials, 2020Co-Authors: Long Yuan, Biyuan Zheng, Jens Kunstmann, Thomas Brumme, Agnieszka Kuc, Shibin Deng, Daria D. Blach, Anlian Pan, Libai HuangAbstract:The nanoscale periodic potentials introduced by moire patterns in semiconducting van der Waals heterostructures have emerged as a platform for designing exciton superlattices. However, our understanding of the motion of excitons in moire potentials is still limited. Here we investigated interlayer exciton dynamics and transport in WS2–WSe2 heterobilayers in time, space and momentum domains using transient absorption microscopy combined with first-principles calculations. We found that the exciton motion is modulated by twist-angle-dependent moire potentials around 100 meV and deviates from normal diffusion due to the interplay between the moire potentials and strong exciton–exciton interactions. Our experimental results verified the theoretical prediction of energetically favourable K–Q interlayer excitons and showed exciton-population dynamics that are controlled by the twist-angle-dependent energy difference between the K–Q and K–K excitons. These results form a basis to investigate exciton and spin transport in van der Waals heterostructures, with implications for the design of quantum communication devices. Interlayer exciton dynamics in a van der Waals heterostructure is found to be modulated by the twist angle between the atomically thin layers, elucidating the effect of moire potentials on exciton motion and providing guidelines to design quantum photonics devices based on 2D materials.
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long range exciton transport and slow annihilation in two dimensional hybrid perovskites
Nature Communications, 2020Co-Authors: Shibin Deng, Long Yuan, Enzheng Shi, Linrui Jin, Letian Dou, Libai HuangAbstract:Two-dimensional hybrid organic-inorganic perovskites with strongly bound excitons and tunable structures are desirable for optoelectronic applications. Exciton transport and annihilation are two key processes in determining device efficiencies; however, a thorough understanding of these processes is hindered by that annihilation rates are often convoluted with exciton diffusion constants. Here we employ transient absorption microscopy to disentangle quantum-well-thickness-dependent exciton diffusion and annihilation in two-dimensional perovskites, unraveling the key role of electron-hole interactions and dielectric screening. The exciton diffusion constant is found to increase with quantum-well thickness, ranging from 0.06 ± 0.03 to 0.34 ± 0.03 cm2 s−1, which leads to long-range exciton diffusion over hundreds of nanometers. The exciton annihilation rates are more than one order of magnitude lower than those found in the monolayers of transition metal dichalcogenides. The combination of long-range exciton transport and slow annihilation highlights the unique attributes of two-dimensional perovskites as an exciting class of optoelectronic materials. Two-dimensional hybrid perovskites are promising excitonic materials; however, there currently lacks understanding on exciton diffusion and annihilation. Here Deng et al. employ transient absorption microscopy to disentangle quantum-well-thickness-dependent exciton transport and annihilation in these materials.
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anomalous interlayer exciton diffusion in twist angle dependent moir e potentials of ws _2 wse _2 heterobilayers
arXiv: Materials Science, 2019Co-Authors: Long Yuan, Biyuan Zheng, Jens Kunstmann, Thomas Brumme, Agnieszka Kuc, Shibin Deng, Daria D. Blach, Anlian Pan, Libai HuangAbstract:The nanoscale periodic potentials introduced by moire patterns in semiconducting van der Waals (vdW) heterostructures provide a new platform for designing exciton superlattices. To realize these applications, a thorough understanding of the localization and delocalization of interlayer excitons in the moire potentials is necessary. Here, we investigated interlayer exciton dynamics and transport modulated by the moire potentials in WS$_2$-WSe$_2$ heterobilayers in time, space, and momentum domains using transient absorption microscopy combined with first-principles calculations. Experimental results verified the theoretical prediction of energetically favorable K-Q interlayer excitons and unraveled exciton-population dynamics that was controlled by the twist-angle-dependent energy difference between the K-Q and K-K excitons. Spatially- and temporally-resolved exciton-population imaging directly visualizes exciton localization by twist-angle-dependent moire potentials of ~100 meV. Exciton transport deviates significantly from normal diffusion due to the interplay between the moire potentials and strong many-body interactions, leading to exciton-density- and twist-angle-dependent diffusion length. These results have important implications for designing vdW heterostructures for exciton and spin transport as well as for quantum communication applications.
Wen-feng Hsieh - One of the best experts on this subject based on the ideXlab platform.
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ultrafast relaxation and absorption saturation at near exciton resonance in a thin zno epilayer
Journal of Applied Physics, 2011Co-Authors: Po-chi Ou, Ja-hon Lin, Wei-rein Liu, Ho-jei Ton, Wen-feng HsiehAbstract:We observed ultrafast free exciton thermalization time of 700–900 fs and obtained the magnitude of maximal differential absorption to be 1.8×104 cm−1 with the pumping fluence of 10 μJ/cm2 by measuring transient differential transmission in a thin ZnO epitaxial layer at room temperature. The largest induced transparency occurs near exciton resonance associated with absorption saturation by comparing the excitation from the above band-gap to band-tail states. The pumping dependent transient absorption reveals transition of excitonic relaxation from exciton-phonon scattering to exciton-exciton scattering or to an electron-hole plasma.
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reducing exciton longitudinal optical phonon coupling with increasing mg incorporation in mgzno powders
Journal of Applied Physics, 2007Co-Authors: Wen-feng HsiehAbstract:The coupling between exciton and longitudinal optical (LO) phonon was investigated in the use of temperature-dependent photoluminescence from MgxZn1−xO powders prepared by a sol-gel method in the range of 0≤x≤0.05. The exciton binding energy increases to 73 meV for 5 at. % Mg incorporated powders. The strength of exciton–LO phonon coupling was deduced from the energy shift of exciton emission with temperature variation. The increase of the exciton binding energy results from a decrease of the exciton Bohr radius that is responsible for reducing the coupling strength of exciton–LO phonon as increasing Mg content.
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reducing exciton longitudinal optical phonon interaction with shrinking zno quantum dots
Applied Physics Letters, 2007Co-Authors: Wen-feng HsiehAbstract:The exciton-longitudinal-optical-phonon (LO-phonon) interaction was observed to decrease with reducing ZnO particle size to its exciton Bohr radius (aB). The unapparent LO-phonon replicas of free exciton (FX) emission and the smaller FX energy difference between 13 and 300K reveal decreasing weighting of exciton-LO phonon coupling strength. The diminished Frohlich interaction mainly results from the reducing aB with size due to the quantum confinement effect that makes the exciton less polar.
Cedric Robert - One of the best experts on this subject based on the ideXlab platform.
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exciton radiative lifetime in transition metal dichalcogenide monolayers
Physical Review B, 2016Co-Authors: Cedric Robert, Gang Wang, D Lagarde, F Cadiz, Benjamin Lassagne, T Amand, Andrea Balocchi, P Renucci, Sefaattin Tongay, B UrbaszekAbstract:©2016 American Physical Society. We have investigated the exciton dynamics in transition metal dichalcogenide monolayers using time-resolved photoluminescence experiments performed with optimized time resolution. For MoSe2 monolayer, we measure τrad0=1.8±0.2ps at T=7K that we interpret as the intrinsic radiative recombination time. Similar values are found for WSe2 monolayers. Our detailed analysis suggests the following scenario: at low temperature (T<50K), the exciton oscillator strength is so large that the entire light can be emitted before the time required for the establishment of a thermalized exciton distribution. For higher lattice temperatures, the photoluminescence dynamics is characterized by two regimes with very different characteristic times. First the photoluminescence intensity drops drastically with a decay time in the range of the picosecond driven by the escape of excitons from the radiative window due to exciton-phonon interactions. Following this first nonthermal regime, a thermalized exciton population is established gradually yielding longer photoluminescence decay times in the nanosecond range. Both the exciton effective radiative recombination and nonradiative recombination channels including exciton-exciton annihilation control the latter. Finally the temperature dependence of the measured exciton and trion dynamics indicates that the two populations are not in thermodynamical equilibrium.
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exciton radiative lifetime in transition metal dichalcogenide monolayers
Physical Review B, 2016Co-Authors: Cedric Robert, Gang Wang, D Lagarde, F Cadiz, Benjamin Lassagne, T Amand, Andrea Balocchi, P Renucci, Sefaattin Tongay, B UrbaszekAbstract:We have investigated the exciton dynamics in transition metal dichalcogenide monolayers using time-resolved photoluminescence experiments performed with optimized time resolution. For $\mathrm{MoS}{\mathrm{e}}_{2}$ monolayer, we measure ${\ensuremath{\tau}}_{\mathrm{rad}}^{0}=1.8\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{0.16em}{0ex}}\mathrm{ps}$ at $T=7\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ that we interpret as the intrinsic radiative recombination time. Similar values are found for $\mathrm{WS}{\mathrm{e}}_{2}$ monolayers. Our detailed analysis suggests the following scenario: at low temperature $(T\ensuremath{\lesssim}50\phantom{\rule{0.16em}{0ex}}\mathrm{K})$, the exciton oscillator strength is so large that the entire light can be emitted before the time required for the establishment of a thermalized exciton distribution. For higher lattice temperatures, the photoluminescence dynamics is characterized by two regimes with very different characteristic times. First the photoluminescence intensity drops drastically with a decay time in the range of the picosecond driven by the escape of excitons from the radiative window due to exciton-phonon interactions. Following this first nonthermal regime, a thermalized exciton population is established gradually yielding longer photoluminescence decay times in the nanosecond range. Both the exciton effective radiative recombination and nonradiative recombination channels including exciton-exciton annihilation control the latter. Finally the temperature dependence of the measured exciton and trion dynamics indicates that the two populations are not in thermodynamical equilibrium.
Junfeng Dai - One of the best experts on this subject based on the ideXlab platform.
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Bound exciton and free exciton states in GaSe thin slab
Scientific Reports, 2016Co-Authors: Chengrong Wei, Xi Chen, Junfeng DaiAbstract:The photoluminescence (PL) and absorption experiments have been performed in GaSe slab with incident light polarized perpendicular to c-axis of sample at 10 K. An obvious energy difference of about 34 meV between exciton absorption peak and PL peak (the highest energy peak) is observed. By studying the temperature dependence of PL and absorption spectra, we attribute it to energy difference between free exciton and bound exciton states, where main exciton absorption peak comes from free exciton absorption, and PL peak is attributed to recombination of bound exciton at 10 K. This strong bound exciton effect is stable up to 50 K. Moreover, the temperature dependence of integrated PL intensity and PL lifetime reveals that a non-radiative process, with activation energy extracted as 0.5 meV, dominates PL emission.
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Bound exciton and free exciton states in GaSe thin slab
arXiv: Mesoscale and Nanoscale Physics, 2016Co-Authors: Chengrong Wei, Xi Chen, Junfeng DaiAbstract:The photoluminescence (PL) and absorption experiments have been performed in GaSe slab with incident light polarized perpendicular to c-axis of sample at 10K. An obvious energy difference of about 34meV between exciton absorption peak and PL peak (the highest energy peak) is observed. By studying the temperature dependence of PL spectra, we attribute it to energy difference between free exciton and bound exciton states, where main exciton absorption peak comes from free exciton absorption, and PL peak are attributed to recombination of bound exciton at 10K. This strong bound exciton effect is stable up to 50K. Moreover, the temperature dependence of integrated PL intensity and PL lifetime reveals that a non-radiative process, with active energy extracted as 0.5meV, dominates PL emission.
