Topic
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: Giant Rabi splitting energies of 91-133 meV can be achieved at ambient conditions, which only involve a small number of excitons, and can pave the way toward active nanophotonic devices operating at room temperature.
Abstract: Strong light-matter coupling manifested by Rabi splitting has attracted tremendous attention due to its fundamental importance in cavity quantum-electrodynamics research and great potentials in quantum information applications. A prerequisite for practical applications of the strong coupling in future optoelectronic devices is an all-solid-state system exhibiting room-temperature Rabi splitting with active control. Here we realized such a system in heterostructure consisted of monolayer WS2 and an individual plasmonic gold nanorod. By taking advantages of the small mode volume of the nanorod and large transition dipole moment of the WS2 exciton, giant Rabi splitting energies of 91-133 meV can be achieved at ambient conditions, which only involve a small number of excitons. The strong light-matter coupling can be dynamically tuned either by electrostatic gating or temperature scanning. These findings can pave the way toward active nanophotonic devices operating at room temperature.
231 citations
TL;DR: Transform-limited linewidths measured on second timescales are reported, primarily on the neutral exciton but also on the charged exciton close to saturation.
Abstract: Developing a quantum photonics network requires a source of very-high-fidelity single photons. An outstanding challenge is to produce a transform-limited single-photon emitter to guarantee that single photons emitted far apart in the time domain are truly indistinguishable. This is particularly difficult in the solid-state as the complex environment is the source of noise over a wide bandwidth. A quantum dot is a robust, fast, bright and narrow-linewidth emitter of single photons; layer-by-layer growth and subsequent nano-fabrication allow the electronic and photonic states to be engineered. This represents a set of features not shared by any other emitter but transform-limited linewidths have been elusive. Here, we report transform-limited linewidths measured on second timescales, primarily on the neutral exciton but also on the charged exciton close to saturation. The key feature is control of the nuclear spins, which dominate the exciton dephasing via the Overhauser field.
230 citations
TL;DR: In this paper, the absorption spectra near a band edge were calculated within the effective mass approximation for the 1D system with a direct allowed or forbidden gap and the Sommerfeld factor was found to be smaller than unity for the direct allowed transition, in contrast to the 3D and 2D cases.
Abstract: We investigate theoretically excitonic effects on the optical properties of one-dimensional (1D) semiconductors. In particular, absorption spectra near a band edge are exactly calculated within the effective-mass approximation for the 1D system with a direct allowed or forbidden gap. We employ two kinds of interaction potentials between an electron and a hole describing a modified Coulomb interaction and a short-range interaction, both of which are free from the well-known divergence problem of the 1D Coulomb system. The Sommerfeld factor, which is the absorption intensity ratio of the unbound (continuum) exciton to the free-electron-hole pair above the band edge, is found to be smaller than unity for the direct allowed transition, in striking contrast to the 3D and 2D cases. This peculiar feature is interpreted in terms of the anomalously strong concentration of the oscillator strength on the lowest discrete exciton state. On the other hand, for the direct forbidden transition, the Sommerfeld factor in the 1D system is larger than unity and shows similar behavior to those in the 3D and 2D cases. These properties hold irrespective of the interaction range of the electron-hole attractive potential. The feasibility of the model potentials is examined, and the Coulomb potential having a cusp-type cutoff is found to be the most effective to describe the potential in an actual semiconductor wire. A dielectric effect in the wire structure is shown to enhance these peculiar features of the 1D system.
230 citations
TL;DR: In this paper, a partially charge-separated electron-hole pair was identified in transition-metal dichalcogenide heteromorphies where the hole resides at the Γ point and the electron is located in a K valley.
Abstract: Monolayers of transition-metal dichalcogenides feature exceptional optical properties that are dominated by tightly bound electron–hole pairs, called excitons. Creating van der Waals heterostructures by deterministically stacking individual monolayers can tune various properties via the choice of materials1 and the relative orientation of the layers2,3. In these structures, a new type of exciton emerges where the electron and hole are spatially separated into different layers. These interlayer excitons4–6 allow exploration of many-body quantum phenomena7,8 and are ideally suited for valleytronic applications9. A basic model of a fully spatially separated electron and hole stemming from the K valleys of the monolayer Brillouin zones is usually applied to describe such excitons. Here, we combine photoluminescence spectroscopy and first-principles calculations to expand the concept of interlayer excitons. We identify a partially charge-separated electron–hole pair in MoS2/WSe2 heterostructures where the hole resides at the Γ point and the electron is located in a K valley. We control the emission energy of this new type of momentum-space indirect, yet strongly bound exciton by variation of the relative orientation of the layers. These findings represent a crucial step towards the understanding and control of excitonic effects in van der Waals heterostructures and devices. A new type of exciton is observed in transition-metal dichalcogenide heterobilayers that is indirect in both real space and momentum space. It consists of a paired electron in MoS2 at the K point and hole spread across MoS2 and WSe2 at the Γ point.
230 citations
TL;DR: In this paper, the phonon energies of the phonons participating in these transitions are 46, 79, 94, and 103 meV, and suggest that the conduction-band minima are at $X$, as predicted by recent calculations.
Abstract: Absorption measurements of cubic SiC at 4.2\ifmmode^\circ\else\textdegree\fi{}K show that the absorption edge is due to indirect, exciton-creating transitions, with an exciton energy gap of 2.390 eV. The energies of the phonons participating in these transitions are 46, 79, 94, and 103 meV, and suggest that the conduction-band minima are at $X$, as predicted by recent calculations. The phonon energies are accurately determined from the 6\ifmmode^\circ\else\textdegree\fi{}K luminescence spectrum of four-particle nitrogen-exciton complexes. Additional lines in the luminescence spectrum at higher temperatures are attributed to thermally excited states of of the complex. Comparisons of cubic SiC with other polytypes are given. There is close agreement in some phonon energies, but energy gaps are very different. An empirical correlation of the energy gaps with percent "hexagonal" is given for seven polytypes.
230 citations