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Exciton
About: Exciton is a research topic. Over the lifetime, 31603 publications have been published within this topic receiving 810642 citations.
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TL;DR: In this article, the authors reported the observation of intervalley biexcitons in the monolayer transition metal dichalcogenides (TMD) using ultrafast pump-probe spectroscopy.
Abstract: Interactions between two excitons can result in the formation of bound quasiparticles, known as biexcitons. Their properties are determined by the constituent excitons, with orbital and spin states resembling those of atoms. Monolayer transition metal dichalcogenides (TMDs) present a unique system where excitons acquire a new degree of freedom, the valley pseudospin, from which a novel intervalley biexciton can be created. These biexcitons comprise two excitons from different valleys, which are distinct from biexcitons in conventional semiconductors and have no direct analog in atomic and molecular systems. However, their valley properties are not accessible to traditional transport and optical measurements. Here, we report the observation of intervalley biexcitons in the monolayer TMD ${\mathrm{MoS}}_{2}$ using ultrafast pump-probe spectroscopy. By applying broadband probe pulses with different helicities, we identify two species of intervalley biexcitons with large binding energies of 60 and 40 meV. In addition, we also reveal effects beyond biexcitonic pairwise interactions in which the exciton energy redshifts at increasing exciton densities, indicating the presence of many-body interactions among them.
172 citations
Journal Article•
TL;DR: In this article, the properties of excitons in monolayer MoS$_2$ from a theoretical point of view were investigated, and it was shown that low energy excitonic states occur both at the Brillouin zone center and at the corners of the two-dimensional hydrogenic model, and that the valley-degenerate exciton doublet splits at finite momentum into an upper mode with nonanalytic linear dispersion and a lower mode with quadratic dispersion.
Abstract: We address the properties of excitons in monolayer MoS$_2$ from a theoretical point of view, showing that low-energy excitonic states occur both at the Brillouin zone center and at the Brillouin-zone corners, that binding energies at the Brillouin-zone center deviate strongly from the $(n-1/2)^{-2}$ pattern of the two-dimensional hydrogenic model, and that the valley-degenerate exciton doublet at the Brillouin-zone center splits at finite momentum into an upper mode with non-analytic linear dispersion and a lower mode with quadratic dispersion. Although monolayer MoS$_2$ is a direct-gap semiconductor when classified by its quasiparticle band structure, it may well be an indirect gap material when classified by its excitation spectra.
172 citations
TL;DR: In this paper, the photoluminescence spectra of ZnO films grown by low pressure metalorganic vapor phase epitaxy (MOPE) were analyzed at 10 K and at room temperature.
Abstract: We report on photoluminescence (PL) spectra of ZnO films grown by low pressure metalorganic vapor phase epitaxy. For PL measurements, high quality ZnO thin films were epitaxially grown on Al2O3(0001) substrates. Time-integrated PL spectra of the films at 10 K clearly exhibited free A and B excitons at 3.376 and 3.382 eV and bound exciton peaks at 3.360, 3.364, and 3.367 eV. With increasing temperature, intensities of the bound exciton peaks drastically decreased and a free exciton peak was dominant above 40 K. Furthermore, time-resolved PL measurements at the free exciton peak were carried out at room temperature. The decay profiles were of double-exponential form, and the decay time constants of 180 ps and 1.0 ns were obtained using a least-square fit of the data.
172 citations
TL;DR: The luminescence spectrum of SrTiO from 1.6 to 3.2 eV has been studied as a function of time elapsed after excitation and it is shown that those values are consistent with what is required for exciton self-trapping.
Abstract: The luminescence spectrum of ${\mathrm{SrTiO}}_{3}$ from 1.6 to 3.2 eV has been studied as a function of time elapsed after excitation. A broad emission band with maximum intensity at 2.44 eV can be observed. The shape of this band, including some fine structure, can be reproduced by the Huang-Rhys model for excitation-lattice interaction. A vibron energy \ensuremath{\Elzxh}\ensuremath{\Omega}=88 meV and a Huang-Rhys factor ${S}_{0}$\ensuremath{\simeq}6 are deduced. It is shown that those values are consistent with what is required for exciton self-trapping. The luminescence intensity has been followed for times between 100 ns and 10 ms. The decay curves indicate that two recombination processes are involved. We associate the first one with self-trapped excitons interacting with acoustic phonons and the second with the retarded formation of self-trapped excitons from localized electrons and holes. The emission appears to be quenched by a nonradiative recombination channel whose activation energy is 0.07 eV.
172 citations
TL;DR: The study demonstrates that the key optoelectronic properties of composite heterostructures comprising electrically coupled metal and semiconductor domains are substantially different from those observed in systems with weak interdomain coupling.
Abstract: The nature of exciton-plasmon interactions in Au-tipped CdS nanorods has been investigated using femtosecond transient absorption spectroscopy. The study demonstrates that the key optoelectronic properties of composite heterostructures comprising electrically coupled metal and semiconductor domains are substantially different from those observed in systems with weak interdomain coupling. In particular, strongly coupled nanocomposites promote mixing of electronic states at semiconductor-metal domain interfaces, which causes a significant suppression of both plasmon and exciton excitations of carriers.
172 citations