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Phononic Casimir corrections for Graphene resonator
摘要： By calculating a Casimir energy for the acoustic phonons of Graphene, we find some temperature-dependent corrections for the pretension of a Graphene sheet suspended on a trench. We obtain values of the order of few mN/m for these corrections in fully as well as doubly clamped Graphene on a narrow trench with one nanometer width, at room temperature. These values are considerable compared to the experimental values, and can increase the fundamental resonance frequency of the Graphene. The values of these corrections increase by increasing the temperature, and so they can be utilized for tuning the Graphene pretension.
关键词： Resonance frequency,Graphene sheet,Casimir energy,Acoustic phonons,Pretension,Nanoelectromechanical systems
更新于2025-09-23 15:23:52
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Giant-Shell CdSe/CdS Nanocrystals: Exciton Coupling to Shell Phonons Investigated by Resonant Raman Spectroscopy
摘要： The interaction between excitons and phonons in semiconductor nanocrystals plays a crucial role in the exciton energy spectrum and dynamics, and thus in their optical properties. We investigate the exciton-phonon coupling in giant-shell CdSe/CdS core-shell nanocrystals via resonant Raman spectroscopy. The Huang-Rhys parameter is evaluated by the intensity ratio of the longitudinal-optical (LO) phonon of CdS with its first multiscattering (2LO) replica. We used four different excitation wavelengths in the range from the onset of the CdS shell absorption to well above the CdS shell band edge to get insight into resonance effects of the CdS LO phonon with high energy excitonic transitions. The isotropic spherical giant-shell nanocrystals show consistently stronger exciton-phonon coupling as compared to the anisotropic rod-shaped dot-in-rod (DiR) architecture, and the 2LO/LO intensity ratio decreases for excitation wavelengths approaching the CdS band edge. The strong exciton-phonon coupling in the spherical giant-shell nanocrystals can be related to the delocalization of the electronic wave functions. Furthermore, we observe the radial breathing modes of the GS nanocrystals and their overtones by ultra-low frequency Raman spectroscopy with nonresonant excitation, using laser energies well below the band gap of the heteronanocrystals, and highlight the differences between higher order optical and acoustic phonon modes.
关键词： Giant-shell nanocrystals,acoustic phonons,Dot-in-rods,Raman spectroscopy,Core-shell heterostructures,exciton-phonon coupling
更新于2025-09-23 15:23:52
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Charge qubit under optical control in a thin semiconductor slab
摘要： The dynamics of a single-electron double quantum dot (charge qubit) in an optical microcavity has been theoretically analysed taking into account the influence of optical and acoustic phonons. The Lamb modes of a two-dimensional mechanical resonator (thin slab) are considered as an example of an acoustic phonon subsystem. It is found that an optical phonon mode can be used as a qubit control tool, similar to the microcavity photon one. The probability of the quantum operation ‘NOT’ has been calculated for two qubit control scenarios: in the microcavity photon field and in the combined photon – phonon field of a microcavity and slab. It is shown that the coherent energy exchange between a qubit and a set of acoustic phonon modes reduces this probability, which depends on the number of modes, the initial state of the phonon field, and the decay rate of modes.
关键词： acoustic phonons,quantum dot,microcavity,quantum computer,qubit
更新于2025-09-23 15:21:21
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Quantum Chip with the Optimized Tunnel Structure for Measuring a Charge Qubit Based on a Double Quantum Dot
摘要： A circuit of a measuring chip for determining an arbitrary pure state of a charge qubit is proposed. The strength of the current flowing through a single-electron transistor in the steady-state mode depends on the state of the qubit. To enhance the sensitivity of the transistor, its working part is built from three quantum dots (QDs) with the energy levels forming a symmetric configuration. The parameters of the system are calculated using a microscopic model of two-dimensional QDs. The time dependences of the population of the structure’s states are obtained and the current strength, sensitivity, and measuring contrast as functions of the geometric parameters of the system are determined. The effect of dissipative processes related to the acoustic phonons on the measurements is investigated and the rates of electron relaxation and dephasing in a two-level system are calculated.
关键词： quantum dot,charge qubit,acoustic phonons,single-electron transistor,quantum detector,electron tunneling
更新于2025-09-23 15:21:01
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Theoretical Investigation of the Shubnikov-de Haas Magnetoresistance Oscillations in a Quantum well under the Influence of Confined Acoustic Phonons
摘要： The Shubnikov – de Haas magnetoresistance oscillations in the Quantum well (QW) under the influence of confined acoustic phonons, The theoretical results show that the conductivity tensor, the complex magnetic impedance of the magnetic field, the frequency, the amplitude of the laser radiation, the QW width, the temperature of the system and especially the quantum index m characterizes the confinement of the phonon. The amplitude of the oscillations of the Shubnikov-de Haas impedance decreases with the increase of the influence of the confined acoustic phonons. The results for bulk phonons in a QW could be achieved, when m goes to zero. We has been compared with other studies when perform the numerical calculations are also achieved for the GaAs/AlGaAs in the QW. Results show that The Shubnikov – de Haas magnetoresistance oscillations amplitude decrease when phonon confinement effect increasing and when width L of the QW increases to a certain value, The Shubnikov – de Haas magnetoresistance oscillations amplitude completely disappears can not be observed.
关键词： Quantum well and width L of quantum well,Confined acoustic phonons,Quantum kinetic equation,Laser radiation,Shubnikov–de Haas magnetoresistance oscillations
更新于2025-09-10 09:29:36
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Coherent optical and acoustic phonons generated at lattice-matched GaP/Si(001) heterointerfaces
摘要： Thin GaP films can be grown on an exact Si(001) substrate with nearly perfect lattice match. We perform all-optical pump-probe measurements to investigate the ultrafast electron-phonon coupling at the buried interface of GaP/Si. Above-bandgap excitation with a femtosecond laser pulse can induce coherent longitudinal optical (LO) phonons both in the GaP overlayer and in the Si substrate. The coupling of the GaP LO phonons with photoexcited plasma is reduced significantly with decreasing the GaP layer thickness from 56 to 16 nm due to the quasi-two-dimensional confinement of the plasma. The same laser pulse can also generate coherent longitudinal acoustic (LA) phonons in the form of a strain pulse. The strain pulses induce not only a periodic modulation in the optical reflectivity as they propagate in the semiconductors, but also a sharp spike when it arrives at the GaP layer boundaries. The acoustic pulse induced at the GaP/Si interface is remarkably stronger than that at the Si surface, suggesting a possible application of the GaP/Si heterostructure as an opto-acoustic transducer. The amplitude and the phase of the reflectivity modulation varies with the GaP layer thickness, which can be understood in terms of the interference caused by the multiple acoustic pulses generated at the top surface and at the buried interface.
关键词： opto-acoustic transducer,GaP/Si heterointerfaces,coherent acoustic phonons,ultrafast electron-phonon coupling,coherent optical phonons
更新于2025-09-09 09:28:46
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Investigation of gold/GaN nanorod arrays for hypersonic detection: The effect of periodicity
摘要： Gold nanodisk arrays on the upper surface of GaN nanorods were developed with the aim of achieving hypersonic imaging with a detection frequency above 10 GHz. In this paper, we report the interesting phenomenon that the hypersonic signal detected by a single gold nanodisk in this structure might be dependent on the array periodicity and rod length. When the array periodicity is of the same order of or longer than the surface hypersonic wavelength, the detected signal would be enhanced by the period-dependent resonance of the surface hypersonic waves scattered by the nanorod/substrate interface. When the array periodicity is smaller than the surface hypersonic wavelength, the coupling of extensional modes between neighboring nanorods, as the detection frequency approaches the coupled-extensional-mode frequency, would enhance the detected signals. Although these enhancements are beneficial to heat transport at nanorod/substrate interfaces, they will cause cross-talk between the neighboring detection rod unit and should be avoided by choosing the correct period for imaging array applications. Our result further indicates that the extensional mode coupling could be avoided by increasing the rod-length to shift the extensional mode frequency away from the detection frequency. This work not only investigates the transport behavior of hypersonic-frequency acoustic phonons at the interface between a bulk material and a nanostructure, but also suggests that the effects of the periodicity and nanorod length need to be taken into consideration for the design of future hypersonic imaging arrays.
关键词： acoustic phonons,periodicity,gold/GaN nanorod arrays,imaging arrays,hypersonic detection
更新于2025-09-09 09:28:46