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Tuning Spontaneous Emission through Waveguide Cavity Effects in Semiconductor Nanowires
摘要： The ability to tailor waveguide cavities and couple them with quantum emitters has developed a realm of nano-photonics encompassing, for example, highly efficient single photon generation or the control of giant photon nonlinearities. Opening new grounds by pushing the interaction of the waveguide cavity and integrated emitters further into the deep subwavelength regime, however, has been complicated by nonradiative losses due to the increasing importance of surface defects when decreasing cavity dimensions. Here, we show efficient suppression of nonradiative recombination for thin waveguide cavities using core?shell semiconductor nanowires. We experimentally reveal the advantages of such nanowires, which host mobile emitters, that is, free excitons, in a one-dimensional (1D) waveguide, highlighting the resulting potential for tunable, active, nanophotonic devices. In our experiment, controlling the nanowire waveguide diameter tunes the luminescence lifetime of excitons in the nanowires across 2 orders of magnitude up to 80 ns. At the smallest wire diameters, we show that this luminescence lifetime can be manipulated by engineering the dielectric environment of the nanowires. Exploiting this unique handle on the spontaneous emission of mobile emitters, we demonstrate an all-dielectric spatial control of the mobile emitters along the axis of the 1D nanowire waveguide.
关键词： Semiconductor nanowire,free excitons,photonic waveguide cavity,subwavelength nanophotonics,luminescence lifetime,tunable spontaneous emission
更新于2025-09-11 14:15:04
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Dynamics of Frenkel Excitons in Pentacene
摘要： The dispersion relation for noninteracting excitons and the in?uence of perturbative corrections are examined in the case of pentacene structure. The values of exchange integrals are determined by nonlinear ?ts to the experimental dispersion data, obtained by the inelastic electron scattering reported in recent experiments. We obtain theoretical dispersion curves along four different directions in the Brillouin zone which possess the same periodicity as the experimental data. We also show that perturbative corrections are negligible since the exciton gap in the dispersion relation is huge in comparison to the exchange integrals.
关键词： exciton-exciton interactions,effective ?eld theory,Heisenberg model,Frenkel excitons
更新于2025-09-10 09:29:36
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Induced Transparency in Plasmon-Exciton Nanostructures for Sensing Applications
摘要： The effect of induced transparency, which is related to photoinduced bleaching of photoabsorbers, is being intensely studied and has many applications in the field of sensing. Along with this classical effect, numerous studies on induced transparency in coupled plasmon–exciton systems, which is accompanied by the formation of hybrid states, have been recently published. The formation of a new coupled system results in various spectral modifications. For example, induced transparency manifests itself as a narrow dip in the absorption spectrum of a coupled system. This effect can be used in sensing, the feasibility of which is the main objective here, where a variety of materials and methods for obtaining the induced transparency are considered. Various morphologies and geometries of plasmonic nanoparticles are discussed as well as types of molecular absorbers to assess the most favorable combinations for the evolvement of induced transparency. The potential applications of the induced transparency effect in sensing and molecular diagnostics are summarized.
关键词： excitons,induced transparency,electromagnetic coupling,plasmons,sensing
更新于2025-09-10 09:29:36
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Multidimensional Coherent Spectroscopy of Semiconductors
摘要： Optical multidimensional coherent spectroscopy (MDCS) is a nonlinear spectroscopy technique where a material is excited by a series of laser pulses to produce a spectrum as a function of multiple frequencies. The technique’s ability to elucidate excited-state structure and interactions has made MDCS a valuable tool in the study of excitons in semiconductors. This review introduces the method and describes progress it has fostered establishing a better understanding of dephasing rates, coherent coupling mechanisms, and many-body interactions pertaining to optically generated electronic excitations in a variety of semiconductor material systems. Emphasis is placed on nanostructured gallium arsenide quantum wells and quantum dots, on quantum dots in other III–V and II–VI semiconductors, and on atomically thin transition metal dichalcogenides. Recent technical advances and potential future directions in the ?eld are also discussed.
关键词： quantum dots,excitons,quantum wells,Fourier-transform spectroscopy,transition metal dichalcogenides
更新于2025-09-10 09:29:36
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Photoluminescence properties of the entire excitonic series in
摘要： We investigated the photoluminescence spectra of Cu2O under photoexcitation at 3.05 eV across the violet band gap. The following three features were found: photoluminescence from blue and violet excitons; photoluminescence from yellow excitons of s, d, and f states in addition to p states with a quantum number up to ten; and emissions associated with the inelastic collision of the 1s yellow excitons. The first process is relevant for the separation of radiative and nonradiative decay rates. The second process likely indicates radiative enhancement of high Rydberg yellow excitons. The last process verifies up-conversion of 1s yellow paraexcitons into higher Rydberg states, which is a critical factor impeding the realization of a high-density paraexciton gas towards transition to the Bose-Einstein condensation.
关键词： photoluminescence,Rydberg states,excitons,Bose-Einstein condensation,Cu2O
更新于2025-09-10 09:29:36
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High-mobility indirect excitons in wide single quantum well
摘要： Indirect excitons (IXs) are bound pairs of electrons and holes confined in spatially separated layers. We present wide single quantum well (WSQW) heterostructures with high IX mobility, spectrally narrow IX emission, voltage-controllable IX energy, and long and voltage-controllable IX lifetime. This set of properties shows that WSQW heterostructures provide an advanced platform both for studying basic properties of IXs in low-disorder environments and for the development of high-mobility excitonic devices.
关键词： spectrally narrow emission,indirect excitons,voltage-controllable energy,wide single quantum well,long lifetime,high mobility
更新于2025-09-10 09:29:36
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Room Temperature Valley Polarization and Coherence in Transition Metal Dichalcogenide-Graphene van der Waals Heterostructures
摘要： Van der Waals heterostructures made of graphene and transition metal dichalcogenides (TMD) are an emerging platform for opto-electronic, -spintronic and -valleytronic devices that could benefit from (i) strong light-matter interactions and spin-valley locking in TMDs and (ii) exceptional electron and spin transport in graphene. The operation of such devices requires significant valley polarization and valley coherence, ideally up to room temperature. Here, using a comprehensive Mueller polarimetry analysis, we report artifact-free room temperature degrees of valley polarization up to 40 % and, remarkably, of valley coherence up to 20 % in monolayer tungsten disulfide (WS2)/graphene heterostructures. At a temperature of 20 K, we measure a record degree of valley coherence of 60 %, a value that exceeds the degree of valley polarization (50 %) and indicates that our samples are minimally affected by pure dephasing processes. Valley contrasts have been particularly elusive in molybdenum diselenide (MoSe2), even at cryogenic temperatures. Upon interfacing monolayer MoSe2 with graphene, the room temperature degrees of valley polarization and coherence are as high as 14 % and 20 %, respectively. Our results are discussed in light of recent reports of highly efficient interlayer exciton and carrier transfer in TMD/graphene heterostructures and hold promise for room temperature chiral light-matter interactions and opto-valleytronic devices.
关键词： Mueller polarimetry,spin-valley locking,Transition metal dichalcogenides,graphene,chiral optics,opto-valleytronics,excitons
更新于2025-09-10 09:29:36
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Bose Condensation of Long-Living Direct Excitons in an Off-Resonant Cavity
摘要： We propose a way to increase the lifetime of two-dimensional direct excitons and show the possibility to observe their macroscopically coherent state at temperatures much higher than that of indirect exciton condensation. For a single GaAs quantum well embedded in photonic layered heterostructures with subwavelength period, we predict the exciton radiative decay to be strongly suppressed. Quantum hydrodynamics joined with the Bogoliubov approach are used to study the Berezinskii-Kosterlitz-Thouless crossover in a finite exciton system with intermediate densities. Below the estimated critical temperatures, drastic growth of the correlation length is shown to be accompanied by a manyfold increase of the photoluminescence intensity.
关键词： Bogoliubov approach,Berezinskii-Kosterlitz-Thouless crossover,Bose condensation,direct excitons,quantum hydrodynamics,off-resonant cavity
更新于2025-09-09 09:28:46
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Can freestanding Xene monolayers behave as excitonic insulators?
摘要： We predict a phase transition in freestanding monolayer Xenes from the semiconducting phase to the excitonic insulating (EI) phase can be induced by reducing an external electric field below some critical value which is unique to each material. The splitting of the conduction and valence bands due to spin–orbit coupling at non-zero electric fields leads to the formation of A and B excitons in the larger or smaller band gap, with correspondingly larger or smaller binding energies. Our calculations show the coexistence of the semiconducting phase of A excitons with the EI phase of B excitons for a particular range of electric field. The dielectric environment precludes the existence of the EI phase in supported or encapsulated monolayer Xenes.
关键词： Monolayer Xenes,Excitonic insulator phase,Excitons
更新于2025-09-09 09:28:46
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Radiative lifetime of localized excitons in transition-metal dichalcogenides
摘要： Disorder derived from defects or local strain in monolayer transition-metal dichalcogenides (TMDs) can lead to a dramatic change in the physical behavior of the interband excitations, producing inhomogeneous spectral broadening and localization leading to radiative lifetime increase. In this study, we have modeled the surface disorder of a monolayer TMD sample through a randomized potential in the layer plane. We show that this model, applied to a monolayer of WSe2, allows us to simulate the spectra of localized exciton states as well as their radiative lifetime. In this context, we give an in depth study of the in?uence of the disorder potential parameters on the optical properties of these defects through energies, density of states, oscillator strengths, photoluminescence (PL) spectroscopy, and radiative lifetime at low temperature (4 K). We demonstrate that localized excitons have a longer emission time than free excitons, in the range of tens of picoseconds or more, the radiative decay time depending strongly on the disorder parameter and dielectric environment. Finally, in order to prove the validity of our model, we compare it to available experimental results of the literature.
关键词： disorder potential,localized excitons,radiative lifetime,transition-metal dichalcogenides,photoluminescence spectroscopy
更新于2025-09-09 09:28:46