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Two-level system damping in a quasi-one-dimensional optomechanical resonator
摘要： Nanomechanical resonators have demonstrated great potential for use as versatile tools in a number of emerging quantum technologies. For such applications, the performance of these systems is restricted by the decoherence of their fragile quantum states, necessitating a thorough understanding of their dissipative coupling to the surrounding environment. In bulk amorphous solids, these dissipation channels are dominated at low temperatures by parasitic coupling to intrinsic two-level system (TLS) defects; however, there remains a disconnect between theory and experiment on how this damping manifests in dimensionally reduced nanomechanical resonators. Here, we present an optomechanically mediated thermal ringdown technique, which we use to perform simultaneous measurements of the dissipation in four mechanical modes of a cryogenically cooled silicon nanoresonator, with resonant frequencies ranging from 3–19 MHz. Analyzing the device’s mechanical damping rate at fridge temperatures between 10 mK and 10 K, we demonstrate quantitative agreement with the standard tunneling model for TLS ensembles con?ned to one dimension. From these ?ts, we extract the defect density of states (P0 ～ 1?4 × 1044 J?1 m?3) and deformation potentials (γ ～ 1–2 eV), showing that each mechanical mode couples on average to less than a single thermally active defect at 10 mK.
关键词： Quantum technologies,Nanomechanical resonators,Optomechanical,Mechanical damping rate,Deformation potentials,Tunneling model,Defect density of states,Two-level system (TLS) defects,Silicon nanoresonator
更新于2025-09-09 09:28:46
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High-Temperature Cycle Durability of Superplastic Al-Zn Eutectoid Solder Joints with Stress Relaxation Characteristics for SiC Power Semiconductor Devices
摘要： We have developed a new high-temperature Al-Zn lead-free soldering process that utilizes superplasticity to realize SiC power devices with high-temperature cycle durability. The joining process consists of an Al-78wt.%Zn preparation being sandwiched by a SiC die and insulation substrate, an interfacial cleaning process at approximately 250-270oC, a heating stage to reach the solid-liquid coexisting temperature of 420-430oC, the ejection of low-melting-temperature β(Zn) from the joining area by press stress, and the transformation to a superplastic composition, i.e., Al-70 wt.% Zn at 270-310oC. Many lamellar phases that enable superplasticity can be formed in this microstructure. This solder joint composition was proven to have a better stress-relaxation effect than eutectic Al-95wt.%Zn, and the composition shows a much higher damping capability at the maximum operating temperature of SiC devices (200oC) than that of other joining candidates. The outstanding temperature cycle durability was verified in temperature cycle tests from -40oC to 300oC for 5000 cycles. This durability is due to the high-stress-relaxation effect from the superplasticity transformation realized by the lamellar structures in the Al-Zn alloy solder.
关键词： lamellar structure,damping capability,power semiconductor,SiC,superplasticity,temperature cycle test,Al-Zn eutectoid solder,lead-free solder,stress relaxation
更新于2025-09-09 09:28:46
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Calculation of the frequency shifts and damping constant for the Raman modes (A$_{1g}$, B$_{1})$ near the tetragonal-cubic transition in SrTiO$_{3}$
摘要： Raman shifts of the soft mode A 1g and the B 1 mode are calculated at various pressures at room temperature for the cubic-tetragonal transition (P C = 9.5 GPa) in SrTiO 3 . This calculation is performed using the observed volume data through the mode Gr(cid:127)uneisen parameters of A 1g and B 1 , which vary with pressure, by (cid:12)tting to the experimental wavenumbers in this crystalline system. Calculated Raman shifts are then used as order parameters to predict the pressure dependence of the damping constant and the inverse relaxation time for the cubic-tetragonal transition in SrTiO 3 . Our predictions from the pseudospin-phonon coupling and the energy (cid:13)uctuation models can be compared with the experimental measurements when available in the literature.
关键词： SrTiO 3,inverse relaxation time,Raman wavenumber,mode Gr(cid:127)uneisen parameter,damping constant
更新于2025-09-04 15:30:14
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Structural Characterization and Room Temperature Low Frequency Raman Scattering from MAPbI3 Halide Perovskite Films Rigidized by Cesium Incorporation
摘要： The structural instability of organometal halide perovskites (OHP) is one of the major issues concerning commercialization of perovskite solar cells. Probing this intrinsic instability is one of the major milestones and challenging tasks towards enhancing the lifespan of the material. Here we have incorporated Cs ions into methylammonium lead iodide (MAPbI3) films and studied the thin film structural and optical properties. Incorporation of Cs into MAPbI3 leads to formation of both α-CsPbI3 and ?-CsPbI3 phases, black and yellow respectively, as indicated by the evolution of the optical band edge and X-Ray diffraction (XRD) spectrum. At a concentration of 20% Cs ions, we observe existence of a stable α-CsPbI3 phase. Incorporating 59% or more Cs ions yields the yellow phase of CsPbI3, due to alloying of Cs with the MAPbI3 matrix. The structural transformations observed in absorption spectra and XRD are confirmed by Low Frequency Raman Spectroscopy. The thermally induced structural fluctuations in pure MAPbI3 films are damped upon Cs incorporation, thus bringing long range stabilized order to the perovskite structure and enabling for the first time observation of Low Frequency Raman Scattering at room temperature for OHPs. In addition to this, Cs incorporation rigidizes the perovskite film and sharpens all low frequency vibrational peaks.
关键词： Cesium incorporation,Low Frequency Raman,Perovskite Stability,Phonon Damping,Hybrid Perovskite
更新于2025-09-04 15:30:14
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trilayers
摘要： Chiral domain walls in ultrathin perpendicularly magnetized layers have a Néel structure stabilized by a Dzyaloshinskii-Moriya interaction (DMI) that is generated at the interface between the ferromagnet and a heavy metal. Different interface materials or properties are required above and below a ferromagnetic film in order to generate the structural inversion asymmetry needed to ensure that the DMI arising at the two interfaces does not cancel. Here we report on the magnetic properties of epitaxial Pt/Co/AuxPt1?x trilayers grown by sputtering onto sapphire substrates with 0.6 nm thick Co. As x rises from 0 to 1, a structural inversion asymmetry is progressively generated. We characterize the epilayer structure with x-ray diffraction and cross-sectional transmission electron microscopy, revealing (111) stacking. The saturation magnetization falls as the proximity magnetization in Pt is reduced, whilst the perpendicular magnetic anisotropy Ku rises. The micromagnetic DMI strength D was determined using the bubble expansion technique and also rises from a negligible value when x = 0 to ～1 mJ/m2 for x = 1. The depinning field at which field-driven domain wall motion crosses from the creep to the depinning regime rises from ～40 to ～70 mT, attributed to greater spatial fluctuations of the domain wall energy with increasing Au concentration. Meanwhile, the increase in DMI causes the Walker field to rise from ～10 to ～280 mT, meaning that only in the x = 1 sample is the steady flow regime accessible. The full dependence of domain wall velocity on driving field bears little resemblance to the prediction of a simple one-dimensional model, but can be described very well using micromagnetic simulations with a realistic model of disorder. These reveal a rise in Gilbert damping as x increases.
关键词： perpendicular magnetic anisotropy,Gilbert damping,Chiral domain walls,domain wall dynamics,Dzyaloshinskii-Moriya interaction
更新于2025-09-04 15:30:14
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AIP Conference Proceedings [Author(s) SolarPACES 2017: International Conference on Concentrating Solar Power and Chemical Energy Systems - Santiago, Chile (26–29 September 2017)] - The SPS and an alternative ring design as pre-booster of FCC e+e? injector
摘要： The FCC-e+e? injector complex needs to produce and to transport a high-intensity e+/e? beam at a fast repetition rate for topping up the collider at its collision energy. Two di?erent options are under consideration as pre-accelerator before the bunches are transferred to the high-energy booster: using the existing SPS and a completely new ring. The purpose of this paper is to present the necessary modi?cations of the existing SPS which is mainly adding damping and Robinson wigglers to reach the required emittance for SPS and the updates on conceptual design of an alternative accelerator ring with injection and extraction energies of 6 and 20 GeV, respectively. In this study, the main parameters of both choices are established, including the optics design and layout updates.
关键词： SPS,Robinson wiggler,FCC-e+e? injector,pre-booster ring,alternative ring design,damping wiggler
更新于2025-09-04 15:30:14