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Optomechanical Cooling in a Continuous System
摘要： Radiation-pressure-induced optomechanical coupling permits exquisite control of micro- and mesoscopic mechanical oscillators. This ability to manipulate and even damp mechanical motion with light—a process known as dynamical backaction cooling—has become the basis for a range of novel phenomena within the burgeoning field of cavity optomechanics, spanning from dissipation engineering to quantum-state preparation. As this field moves toward more complex systems and dynamics, there has been growing interest in the prospect of cooling traveling-wave phonons in continuous optomechanical waveguides. Here, we demonstrate optomechanical cooling in a continuous system for the first time. By leveraging the dispersive symmetry breaking produced by intermodal Brillouin scattering, we achieve continuous-mode optomechanical cooling in an extended 2.3-cm silicon waveguide, reducing the temperature of a band of traveling-wave phonons by more than 30 K from room temperature. This work reveals that optomechanical cooling is possible in macroscopic linear waveguide systems without an optical cavity or discrete acoustic modes. Moreover, through an intriguing type of wave-vector-resolved phonon spectroscopy, we show that this system permits optomechanical control over continuously accessible groups of phonons and produces a new form of nonreciprocal reservoir engineering. Beyond this study, this work represents a first step toward a range of classical and quantum traveling-wave operations in continuous optomechanical systems.
关键词： Waveguide,Brillouin scattering,Optomechanics,Phonon cooling,Silicon
更新于2025-09-09 09:28:46
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Fine structure in high resolution 4f7?4f65d excitation and emission spectra of X-ray induced Eu2+ centers in LuPO4:Eu sintered ceramics
摘要： X-ray induced effects in LuPO4:Eu3+ sintered thermoluminescent material were investigated by absorption and photoluminescence measurements between 20-300 K. Evidence for Eu3+→Eu2+ conversion upon exposure to X-rays was obtained as narrow band blue Eu2+ photoluminescence was observed. The low temperature luminescence of Eu2+ ions in X-rayed LuPO4:Eu ceramics showed a unique fine structure with a sharp zero-phonon line at 425.8 nm and well-resolved vibronic structure. Excitation spectra of the Eu2+ luminescence revealed a rich structure in which individual 4f7→ 4f6(7FJ)5d1 zero-phonon lines accompanied by vibronic transitions were identified. A detailed analysis allowed an accurate calculation of the Eu3+-like 4f6(7FJ) core levels in the 4f65d1 excited configuration. The 4f6 core splitting is different from that of the 7FJ states for Eu3+ in LuPO4, providing evidence for the role of 4f6-5d interaction on the splitting of the 4f6 configuration. The unique luminescence of Eu2+ with a small Stokes shift and well-determined energies of 4f6(7FJ)5d1 excited states make LuPO4:Eu a model system for testing theoretical models which are presently developed to calculate and predict the energy level structure and Stokes shift of 4fn-4fn-15d1 transitions of lanthanides.
关键词： Eu2+ luminescence,LuPO4,zero-phonon line,high resolution spectroscopy,4f65d excited state
更新于2025-09-09 09:28:46
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Broadband Terahertz Spectroscopy of Phonon-Polariton Dispersion in Ferroelectrics
摘要： Electromagnetic waves at frequencies below the X-ray region strongly couple to the optical vibrational modes in a solid. These coupled excitations have been called phonon polaritons. The relationship of the polariton frequency versus the polariton wavevector shows a remarkable dispersion, especially in the vicinity of the transverse and longitudinal optical mode frequencies. The signi?cant frequency dependence enables valuable applications such as a tunable terahertz radiation source. The polariton dispersion relations of technologically important dielectric and ferroelectric crystals were reviewed in the broad terahertz range using terahertz time-domain spectroscopy, far-infrared spectroscopy, and Raman scattering spectroscopy.
关键词： terahertz,phonon polariton,ferroelectrics,spectroscopy
更新于2025-09-09 09:28:46
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Thermopower of a Two-Dimensional Semimetal in a HgTe Quantum Well
摘要： The thermopower in a two-dimensional semimetal existing in HgTe quantum wells 18–21 nm thick has been studied experimentally and theoretically for the first time. It has been found theoretically and experimentally that the thermopower has two components—diffusion and phonon-drag—and that the second component is several times larger than the first. It has been concluded that the electron–hole scattering plays an important role in both mechanisms of the thermopower.
关键词： diffusion,thermopower,HgTe quantum wells,two-dimensional semimetal,phonon-drag,electron–hole scattering
更新于2025-09-09 09:28:46
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Gallium Oxide || Low-field and high-field transport in β-Ga2O3
摘要： β-Ga2O3 has recently emerged as a novel wide-bandgap semiconductor with immense potential for applications in power electronics and optoelectronics. Experimental advancements in the past 5 years have been significant toward realizing commercial β-Ga2O3 devices in the near future [1–7]. Matured crystal growth and processing techniques make the material further promising [8–10]. In terms of power electronic applications, MOSFETs based on this material have been demonstrated that could withstand record high voltages [11, 12]. The accuracy of n-type doping and the difficulty of p-type doping make electrons the primary charge carriers in β-Ga2O3. Although β-Ga2O3 has lower electron mobility compared to other wide-bandgap semiconductors, it is found to have a superior Baliga’s figure of merit that jointly accounts for on-state resistance and breakdown voltage [4]. So it is important to investigate in rigor the fundamentals behind β-Ga2O3 material properties that could be beneficial to gain an understanding on the causes that control mobility and breakdown voltage. There are theoretical reports on fundamental materials aspects including electronic structure [13] and optical properties [14], lattice dynamical and dielectric properties [15], and thermal properties [16, 17] as well. The primary physics behind both mobility (and hence the device on resistance) and breakdown voltage lies in the electron transport phenomenon. There have been a few experimental reports that try to characterize the electron transport and scattering mechanisms in β-Ga2O3 with Hall measurements being reported a few times to predict temperature dependence and also crystal orientation dependence of the electron mobility [18, 19]. On the other hand, we are making a systemic study on the theoretical understanding of electron transport in β-Ga2O3 starting from the first principles [20–22]. The main idea is to follow a bottom-up approach in order to develop an understanding of the near-equilibrium and far-from-equilibrium electron dynamics in β-Ga2O3. This is unique compared to conventional semiconductors in a way that β-Ga2O3 has a low-symmetry crystal structure and a fairly large primitive unit cell that gives rise to many phonon modes. On several occasions, the traditional notions of electron transport that are applicable to Si and GaAs actually do not quite hold well in the case of β-Ga2O3. In this chapter, we attempt to provide a comprehensive picture of electron transport in β-Ga2O3 under low and moderately high electric fields based on our work in the recent years.
关键词： electron-phonon interaction,β-Ga2O3,electron mobility,power electronics,optoelectronics,electron transport,velocity-field curves,wide-bandgap semiconductor
更新于2025-09-09 09:28:46
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Oriented Asymmetric Wave Propagation and Refraction Bending in Hyperbolic Media
摘要： Crystal quartz is a well-known anisotropic medium with optically active phonons in the THz region where hyperbolic phonon-polaritons can be excited. Here, we use this material to illustrate how the behavior of bulk and surface hyperbolic polaritons can be drastically modified by changing the orientation of the crystal’s anisotropy axis with respect to its surface. We demonstrate, both theoretically and experimentally, phenomena associated with the orientation of hyperbolic media. We show the consequences of changes in the crystal’s orientation in various ways, such as the modification of the effective reststrahl regions and associated surface phonon polariton dispersion. Of particular significance, however, is the transmission behavior of radiation passing through a rotated hyperbolic crystal. Here, even a small rotation of the optical axes with respect to the crystal surface can lead to a very large degree of asymmetry in the transmitted intensity. In addition, the refracting angle (which in a hyperbolic medium may correspond to negative refraction and slab lensing behavior) itself becomes asymmetric, so that a slab lens with a laterally displaced image becomes possible. We discuss some of the possible consequences of these types of effects.
关键词： Surface Polaritons,Hyperbolic Media,Attenuated Total Reflection,Negative Refraction,Phonon-Polaritons
更新于2025-09-09 09:28:46
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Floquet scattering of light and sound in Dirac optomechanics
摘要： The inelastic scattering and conversion process between photons and phonons by laser-driven quantum dots is analyzed for a honeycomb array of optomechanical cells. Using Floquet theory for an effective two-level system, we solve the related time-dependent scattering problem, beyond the standard rotating-wave approximation approach, for a plane Dirac-photon wave hitting a cylindrical oscillating barrier that couples the radiation field to the vibrational degrees of freedom. We demonstrate different scattering regimes and discuss the formation of polaritonic quasiparticles. We show that sideband-scattering becomes important when the energies of the sidebands are located in the vicinity of avoided crossings of the quasienergy bands. The interference of Floquet states belonging to different sidebands causes a mixing of long-wavelength (quantum) and short-wavelength (quasiclassical) behavior, making it possible to use the oscillating quantum dot as a kind of transistor for light and sound. We comment under which conditions the setup can be utilized to observe zitterbewegung.
关键词： Dirac optomechanics,photon-phonon conversion,Floquet scattering,polaritonic quasiparticles,quantum dots
更新于2025-09-09 09:28:46
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Decoupling Carrier Concentration and Electron-Phonon Coupling in Oxide Heterostructures Observed with Resonant Inelastic X-Ray Scattering
摘要： We report the observation of multiple phonon satellite features in ultrathin superlattices of the form nSrIrO3=mSrTiO3 using resonant inelastic x-ray scattering (RIXS). As the values of n and m vary, the energy loss spectra show a systematic evolution in the relative intensity of the phonon satellites. Using a closed-form solution for the RIXS cross section, we extract the variation in the electron-phonon coupling strength as a function of n and m. Combined with the negligible carrier doping into the SrTiO3 layers, these results indicate that the tuning of the electron-phonon coupling can be effectively decoupled from doping. This work both showcases a feasible method to extract the electron-phonon coupling in superlattices and unveils a potential route for tuning this coupling, which is often associated with superconductivity in SrTiO3-based systems.
关键词： superlattices,electron-phonon coupling,SrTiO3,SrIrO3,resonant inelastic x-ray scattering
更新于2025-09-09 09:28:46
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Detection of oxygen sub-lattice ordering in A-site deficient perovskites through monochromated core-loss EELS mapping
摘要： Perovskite oxides are widely studied for a variety of applications, from thermoelectrics to fuel cells. Part of the attraction lies in the fact that perovskite ceramics are relatively easy to dope chemically over a wide range of compositions, resulting in various degrees of structural ordering. As a consequence, the properties and functionalities of such materials can be readily tailored. For instance in systems proposed for thermoelectric applications, the presence of superlattices, or domain boundaries vacancies can suppress the thermal conductivity due to increased phonon scattering. Understanding therefore the mechanisms behind the formation of such types of ordering in ceramic systems is crucial for their implementation in engineering applications. Here, we report on an A-site deficient perovskite system based on the Nd2/3xTiO3 double perovskite. This system, a candidate for thermoelectric applications, has attracted significant attention due to the presence of a peculiar superstructure originating in part in A-site cation vacancy ordering. Using aberration corrected Scanning Transmission Electron Microscopy we investigate a series of Nd2/3xTiO3 ceramics engineered to possess different degrees of A-site cation-vacancy ordering and as a result vastly different thermoelectric properties. Annular Bright Field Imaging of the [110] orientation, preformed in the Nion UltraSTEM 100TM reveals the presence of tilting domains in the TiO6 sub lattice, dependent on the A-site occupancy. Furthermore, advanced image analysis of the electron micrographs was used to measure local distortions in the TiO6 lattice. The presence of these octahedral distortions was further investigated by employing atomically resolved monochromated core loss Electron Energy Loss measurements, acquired with an energy resolution better than 0.100eV, using the Nion UltraSTEM 100MC TM instrument. With this approach it is not only possible to map individual components of the Ti L2,3 near edge fine structure, but also fine local changes in the ELNES; subtle changes Ti L2,3 pre-peak intensity – usually not discernible in conventional EELS measurements as well as changes in the Ti L3 eg/tg and tg L3/L2 intensity ratios all indicative of local TiO6 distortions.
关键词： Annular Bright Field Imaging,aberration corrected Scanning Transmission Electron Microscopy,Nd2/3xTiO3,structural ordering,Electron Energy Loss measurements,thermoelectrics,fuel cells,A-site deficient perovskite,phonon scattering,perovskite oxides
更新于2025-09-09 09:28:46
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Anomalous K-Point Phonons in Noble Metal/Graphene Heterostructure Activated by Localized Surface Plasmon Resonance
摘要： Metal/graphene interface has been one of the most important research topics with regard to charge screening, charge transfer, contact resistance, and solar cells. Chemical bond formation of metal/graphene can be deduced from the defect induced D-band and its second-order mode, 2D band, measured by Raman spectroscopy, as a simple and non-destructive method. However, a phonon mode located at ~ 1350 cm-1, which is normally known as the defect-induced D-band, is intriguing for graphene deposited with noble metals (Ag, Au, and Cu). We observe anomalous K-point phonons in non-reactive noble metal/graphene heterostructure. The intensity ratio of the mid-frequency mode at ~ 1350 cm-1 over G-band (~1590 cm-1) exhibits non-linear but resonant behavior with the excitation laser wavelength and more importantly, the phonon frequency–laser energy dispersion is ~ 10-17 cm-1/eV, which is much less than the conventional range. These phonon modes of graphene at non-zero phonon wave vector (q ≠ 0) around K points are activated by localized surface plasmon resonance, and not by the defects due to chemical bond formation of metal/graphene. This hypothesis is supported by density function theory (DFT) calculations for noble metals and Cr along with the measured contact resistances.
关键词： K-point phonon,Raman,graphene,localized surface plasmon,noble metal
更新于2025-09-09 09:28:46