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Optical vibration modes in multi-layer quantum dots of polar ternary mixed crystals
摘要： Within the framework of the dielectric continuum approach and the modified random-element isodisplacement model, the optical vibration modes as well as the corresponding electron-phonon interactions in spherical multi-layer quantum dots (QDs) consisting of ternary mixed crystals (TMCs) are investigated in detail. The dispersion relation and electron-phonon interaction Hamiltonian are obtained. As applications of the present theory, the numerical calculations for the ZnS/ZnxCd1-xS/ZnS and GaAs/AlxGa1-xAs/GaAs QDs are performed and discussed. Considering the "one-mode" and "two-mode" behaviors of the TMCs, the results show that there are 5 and 7 branches of interface/surface optical (IO/SO) phonon modes in the two systems, respectively. It is found that the effects of TMCs have a remarkable influence on the optical phonon frequencies and the electron-phonon interactions. The results also reveal that the presence of the cap layer introduces significant influence on the TMCs effects of optical phonon in multi-layer QDs. We hope that our theoretical results can stimulate further investigations of related photoelectric properties, as well as device applications in multi-layer QDs consisting of TMCs.
关键词： ternary mixed crystal,electron-phonon interaction,optical vibration mode,multi-layer quantum dot
更新于2025-09-23 15:21:01
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Interaction of Rydberg excitons in cuprous oxide with phonons and photons: optical linewidth and polariton effect
摘要： We demonstrate that the optical linewidth of Rydberg excitons in Cu2O can be completely explained by scattering with acoustical and optical phonons, whereby the dominant contributions stems from the non-polar optical 3G- and 5G- modes. The consequences for the observation of polariton effects are discussed. We find that an anti-crossing of photon and exciton dispersions exists only for states with main quantum numbers n > 28, so polariton effects do not play any role in the experiments reported up to now.
关键词： polaritons,phonon scattering,Rydberg excitons,cuprous oxide
更新于2025-09-23 15:21:01
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Raman spectrum of nanocrystals: Phonon dispersion splitting and anisotropy
摘要： The effects of anisotropy and splitting of the phonon dispersions in the Raman spectrum of nanocrystals are investigated. We describe the different branches of the optical phonon dispersion curves along each high-symmetry direction by fitting a simple empirical model to experimental data. These curves are then used to calculate the Raman spectrum in the framework of the phonon confinement model and the results are compared with a wide range of available experimental data as well as with the spectra predicted by currently available models based on a single isotropic dispersion curve. We show that by considering the anisotropy and splitting of rigorously obtained optical phonon dispersions, the commonly observed deviations between experimental and theoretical data are strongly reduced. Our work enables the extraction of significantly more accurate information about relevant physical properties of nanocrystals from Raman spectroscopy.
关键词： splitting,anisotropy,nanocrystals,phonon dispersion,Raman spectrum
更新于2025-09-23 15:21:01
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-type PbTe from first principles
摘要： We present an ab initio study that identifies the main electron-phonon scattering channels in n-type PbTe. We develop an electronic transport model based on the Boltzmann transport equation within the transport relaxation time approximation, fully parametrized from first-principles calculations that accurately describe the dispersion of the electronic bands near the band gap. Our computed electronic mobility as a function of temperature and carrier concentration is in good agreement with experiments. We show that longitudinal optical phonon scattering dominates electronic transport in n-type PbTe, while acoustic phonon scattering is relatively weak. We find that scattering due to soft transverse optical phonons is by far the weakest scattering mechanism, due to the symmetry-forbidden scattering between the conduction band minima and the zone center soft modes. Soft phonons thus play the key role in the high thermoelectric figure of merit of n-type PbTe: they do not degrade its electronic transport properties although they strongly suppress the lattice thermal conductivity. Our results suggest that materials like PbTe with soft modes that are weakly coupled with the electronic states relevant for transport may be promising candidates for efficient thermoelectric materials.
关键词： electron-phonon scattering,transport relaxation time approximation,thermoelectric materials,Boltzmann transport equation,n-type PbTe
更新于2025-09-23 15:21:01
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Apparent Spectral Shift of Thermally Generated Surface Phonon-Polariton Resonance Mediated by a Nonresonant Film
摘要： The physical origin of the spectral shift of a thermally generated surface phonon-polariton (SPhP) resonance of a silicon carbide (SiC) bulk mediated by a nonresonant film is explained. The local density of electromagnetic states (LDOS) in a nonresonant intrinsic silicon (Si) film due to thermal emission by SiC, derived using fluctuational electrodynamics, exhibits a local maximum near the SPhP-resonant frequency in addition to a lower frequency resonance generated by gap modes emerging in the vacuum gap separating the SiC and Si layers. Multiple reflections within the vacuum gap also induce a LDOS drop around the SPhP-resonant frequency. As a result, depending on the film thickness to vacuum gap ratio and the location where the LDOS is calculated in the film, the low-frequency resonance can dominate the LDOS, such that the SPhP resonance appears to be redshifted. A similar spectral behavior is observed on the monochromatic radiative heat flux absorbed by the Si film. It is shown that apparent spectral (red and blue) shifts of the SPhP resonance mediated by a nonresonant film are bounded by the transverse and longitudinal optical phonon frequencies of SiC. This work is of importance in applications involving dissimilar materials, such as thermophotovoltaics and thermal rectification, where gap modes may significantly disrupt flux resonance. Gap modes may also be at the origin of the resonance redshift systematically observed in near-field thermal spectroscopy.
关键词： local density of electromagnetic states,thermal emission,surface phonon-polariton,spectral shift,near-field thermal spectroscopy
更新于2025-09-23 15:21:01
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Temperature Dependence of Phonon Modes, Optical Constants, and Optical Band Gap in Two-Dimensional ReS2 Films
摘要： Effects of temperature on the optical properties of the large area ReS2 films (ten layers), which is prepared by chemical vapor deposition on SiO2/Si substrates, have been investigated by Raman and reflectance spectra. The phonon frequencies of eighteen Raman modes redshift about 3 cm-1 with increasing the temperature from 140 K to 320 K. The optical constants (n and k) at a photon energy region of 0.46-6.52 eV are obtained, and the values blue-shift with increasing temperature. Four interband transitions (Ep1, Ep2, Ep3, and Ep4) are observed at 1.53 eV, 2.98 eV, 4.25 eV, and 5.37 eV at 303 K, and the values increase with increasing the temperature. The physical origins have been assigned to the different band-to-band direct electronic transitions. The optical band gap of the ReS2 films increases from 1.36 eV at 303 K to 1.38 eV at 383 K. Based on the first-principles calculation results, the band gap increases from 1.32 eV at a normal lattice constant to 1.40 eV at 1.1 times lattice constant. This is because the energy levels present the tendencies of degeneracy, which due to the coupling between Re 5d orbital and S 3p orbital is weaker and the energy level splitting is smaller with increasing temperature.
关键词： optical constants,ReS2 films,2D materials,phonon modes,optical band gap
更新于2025-09-23 15:21:01
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Near-ultraviolet Raman and micro-Raman analysis of electronic materials
摘要： Raman and micro-Raman analysis methods have been extensively investigated for the study of materials used in electronic and photonic devices. Raman studies are used to understand fundamental phonon properties, along with effects related to the crystal structure, disorder, doping, and external factors such as temperature and stress. Micro-Raman extends these investigations to the micron scale. This article reviews diverse benefits of Raman measurements when carried out using laser excitation in the near-ultraviolet wavelength range, nominally 400 to 325 nm. Micro-Raman methods in the near ultraviolet exploit the key advantage of reduced focal spot size, achievable at shorter wavelengths when using diffraction-limited optics, for mapping with high spatial resolution. There are distinct advantages common to Raman and micro-Raman spectroscopy in the near ultraviolet when compared to the widely used visible excitation. One advantage exploits the shallower optical penetration depth in select materials for probing near-surface regions or interfaces. A second advantage is related to tuning of the excitation photon energy relative to the electronic levels of a material for investigating resonance effects. Finally, the application of Raman scattering to materials which exhibit strong fluorescence requires tuning to a wavelength range away from the potentially obscuring emission. This article overviews several examples of these key advantages to study diverse applied physics problems in electronic and photonic materials. Topics covered include stress mapping in silicon and related materials, stress and thermal effects in gallium nitride and other group-III-nitride semiconductors, and carbon materials ranging from graphite and graphene to diamond grown using chemical vapor deposition. The fundamental effects of stress- and temperature-induced shifts in phonon energies and their application to study epitaxy and device-related effects are also briefly reviewed.
关键词： near-ultraviolet,stress mapping,carbon materials,chemical vapor deposition,phonon properties,Raman spectroscopy,electronic materials,micro-Raman,gallium nitride
更新于2025-09-23 15:21:01
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Coherent phonon lasing in a thermal quantum nanomachine
摘要： The notion of nanomachines has recently emerged to engage and use collective action of ensembles of nanoscale components or systems. Here we present a heat-gradient driven nanomachine concept which through appropriate coupling between quantum nanosystems is capable of realizing and maintaining an inversion. Based on a Lindblad form of the quantum master equation with a semiclassical coupling to the lattice displacement phonon field we show that this positive inversion can be harnessed to generate coherent optomechanical oscillations and phonon lasing.
关键词： heat-gradient,nanomachines,quantum nanosystems,quantum master equation,Lindblad form,phonon lasing
更新于2025-09-23 15:21:01
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Quantum correlation and squeezing dynamics of a dissipative nonlinear optomechanical oscillator: Heisenberg-Langevin approach
摘要： In this paper, an optomechanical cavity that is quadratically coupled to the cavity ?eld and formed by a micropillar with Bragg re?ectors and a thin dielectric membrane, is studied. In addition, it is considered that this interaction occurs in the presence of Kerr medium, external laser ?eld and damping e?ects (for cavity ?eld and moving Bragg re?ector). Using the Heisenberg-Langevin approach, the dynamics of quantum correlation functions (for cavity ?eld and moveable re?ector) and squeezing parameters for quadratures of the cavity ?eld are investigated. In each case, the in?uences of optomechanical coupling, detuning parameter, thermal mean number of cavity photons and phonons, damping parameters and Kerr medium on the above nonclassicality features are analyzed in detail. It is illustrated that the amount of the above-mentioned physical phenomena can be controlled by appropriately choosing the evolved parameters. Also, we show that photon and phonon blockades emerge in some special cases.
关键词： squeezing dynamics,quantum correlation,photon blockade,optomechanical cavity,Kerr medium,Heisenberg-Langevin approach,phonon blockade
更新于2025-09-23 15:21:01
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Long coherent dynamics of localized excitons in (In,Ga)N/GaN quantum wells
摘要： We study the coherent dynamics of localized excitons in 100 periods of 2.5-nm-thick (In,Ga)N/GaN quantum wells with 7.5% indium concentration, measured with spectroscopic resolution through two-pulse and three-pulse photon echoes at the temperature of 1.5 K. A long-lived coherent exciton dynamics is observed in the (In,Ga)N quantum wells: When the laser photon energy is tuned across the 43-meV-wide inhomogeneously broadened resonance line, the coherence time T2 varies between 45 and 255 ps, increasing with stronger exciton localization. The corresponding narrow homogeneous linewidths ranging from 5.2 to 29 μeV as well as the relatively weak exciton-phonon interaction (0.7 μeV/K) confirm a strong, quantum-dot-like exciton localization in a static disordered potential inside the (In,Ga)N quantum well layers.
关键词： localized excitons,photon echoes,exciton-phonon interaction,coherent dynamics,(In,Ga)N/GaN quantum wells
更新于2025-09-23 15:21:01