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Experimental evidence of crystal-field, Zeeman-splitting, and spin-phonon excitations in the quantum supersolid Na2BaCo(PO4)2

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Physical Review B 2025年第15期111卷 155129-155129页

作者： Ghulam Hussain Jianbo Zhang Man Zhang Lalit Yadav Yang Ding Changcheng Zheng Sara Haravifard Xiawa Wang Division of Natural and Applied Sciences Duke Kunshan University Kunshan Jiangsu 215316 China Center for High-Pressure Science and Technology Advanced Research Beijing 100094 China Department of Physics Duke University Durham North Carolina 27708 USA Department of Mechanical Engineering and Materials Science Duke University Durham North Carolina 27708 USA

Drawing inspiration from the recent breakthroughs in the Na2BaCo(PO4)2 quantum magnet, renowned for its spin supersolidity phase and its potential for solid-state cooling applications, our study delves into the interplay among lattice, spin, and orbital degrees of freedom within this compound. Using temperature-, field-, and pressure-dependent Raman scattering techniques, we present experimental evidence revealing crystal-electric-field (CEF) excitations, alongside the interplay of CEF-phonon interactions. We performed density functional theory calculations for the phonon frequencies and compared them with the experimentally observed modes. In addition, our experiments elucidated electronic transitions from j1/2 to j3/2 and from j1/2 to j5/2, with energy levels closely aligned with theoretical predictions based on point-charge models. Moreover, the application of a magnetic field and pressure revealed Zeeman splittings characterized by Landé-g factors as well as the CEF-phonon resonances. The anomalous shift in the coupled peak at low temperatures originated from the hybridization of CEF and phonon excitations due to their close energy proximity and shared symmetry. These findings constitute a significant step towards unraveling the fundamental properties of this exotic quantum material for future research in fundamental physics or engineering application.

关键词： Degrees of freedom (mechanics)

Experimental observation of ballistic to diffusive transition in AlN thin films

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arXiv 2024年

作者： Hoque, Md Shafkat Bin Liao, Michael E. Zare, Saman Liu, Zeyu Koh, Yee Rui Huynh, Kenny Shi, Jingjing Graham, Samuel Luo, Tengfei Ahmad, Habib Doolittle, W. Alan Goorsky, Mark S. Hopkins, Patrick E. Department of Mechanical and Aerospace Engineering University of Virginia CharlottesvilleVA22904 United States Department of Materials Science and Engineering University of California Los AngelesCA90095 United States Department of Applied Physics Hunan University Changsha410300 China George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology AtlantaGA30332 United States School of Materials Science and Engineering Georgia Institute of Technology AtlantaGA30332 United States Department of Aerospace and Mechanical Engineering University of Notre Dame Notre DameIN46556 United States School of Electrical and Computer Engineering Georgia Institute of Technology AtlantaGA30332 United States Department of Materials Science and Engineering University of Virginia CharlottesvilleVA22904 United States Department of Physics University of Virginia CharlottesvilleVA22904 United States

Bulk AlN possesses high thermal conductivity due to long phonon mean-free-paths, high group velocity, and long lifetimes. However, the thermal transport scenario becomes very different in a thin AlN film due to phonon-defect and phonon-boundary scattering. Herein, we report experimental observation of ballistic to diffusive transition in a series of AlN thin films (1.6 - 2440 nm) grown on sapphire substrates. The ballistic transport is characterized by constant thermal resistance as a function of film thickness due to phonon scattering by defects and boundaries. In this transport regime, phonons possess very small group velocities and lifetimes. The lifetime of the optical phonons increases by more than an order of magnitude in the diffusive regime, however, remains nearly constant afterwards. Our study is important for understanding the details of nano and microscale thermal transport in a highly conductive material. Copyright © 2024, The Authors. All rights reserved.

关键词： Sapphire

MCTrans++: A 0-D Model for Centrifugal Mirrors

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arXiv 2023年

作者： Schwartz, Nick R. Abel, Ian G. Hassam, Adil B. Kelly, Myles Romero-Talamás, Carlos A. Department of Materials Science and Engineering University of Maryland College ParkMD20742 United States Institute for Research in Electronics and Applied Physics University of Maryland College ParkMD20742 United States Department of Physics University of Maryland College ParkMD20742 United States Department of Mechanical Engineering University of Maryland College ParkMD20742 United States Department of Mechanical Engineering University of Maryland Baltimore CountyMD21250 United States

The centrifugal mirror confinement scheme incorporates supersonic rotation of a plasma into a magnetic mirror device. This concept has been shown experimentally to drastically decrease parallel losses and increase plasma stability as compared to prior axisymmetric mirrors. MCTrans++ is a 0D scoping tool which rapidly models experimental operating points in the Centrifugal Mirror Fusion Experiment (CMFX) at the University of Maryland. In the low-collisionality regime, parallel losses can be modeled analytically. A confining potential is set up that is partially ambipolar and partially centrifugal. Due to the stabilizing effects of flow-shear, the perpendicular losses can be modeled as classical. Radiation losses such as Bremsstrahlung and cyclotron emission are taken into account. A neutrals model is included, and, in some circumstances, charge-exchange losses are found to exceed all other loss mechanisms. We use the SUNDIALS ARKODE library to solve the underlying equations of this model;the resulting software is suitable for scanning large parameter spaces, and can also be used to model time-dependent phenomena such as a capacitive discharge. MCTrans++ has been used to verify results from prior centrifugal mirrors, create an experimental plan for CMFX, and find configurations for future reactor-scale fusion devices. Copyright © 2023, The Authors. All rights reserved.

关键词： Mirrors

Heat capacity and relaxation dynamics of glassy films: A lattice model study

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Physical Review E 2025年第1期111卷 015406-015406页

作者： Qiang Zhai Xin-Yuan Gao Hai-Yao Deng Chun-Shing Lee Sen Yang Ke Yan Chi-Hang Lam MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter School of Physics Xi'an Jiaotong University Xi'an Shaanxi 710049 China Department of Physics The Chinese University of Hong Kong Shatin New Territories Hong Kong China School of Physics and Astronomy Cardiff University 5 The Parade Cardiff CF24 3AA Wales United Kingdom School of Science Harbin Institute of Technology (Shenzhen) Shenzhen 518055 China School of Mechanical Engineering Xi'an Jiaotong University Xi'an Shaanxi 710049China Department of Applied Physics Hong Kong Polytechnic University Hong Kong China

We study the calorimetric properties and structural relaxation of glassy films using a distinguishable particle lattice model (DPLM). We determine the glass transition temperature versus film thickness from the heat capacity during heating as well as from the local relaxation time. The results based on both approaches are in good agreement with the experimentally observed Keddie-Cory-Jones relation. The thus demonstrated interplay between calorimetric properties and structural relaxation is further corroborated by successfully reconstructing the simulated heat capacity during heat and cooling from the local relaxation times. Our results suggest DPLM as a useful lattice model for studying glassy films.

关键词： Glass transition

Emergent facilitation by random constraints in a facilitated random walk model of glass

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arXiv 2024年

作者： Lam, Leo S.I. Deng, Hai-Yao Zhang, Wei-Bing Nwankwo, Udoka Xiao, Chu Yip, Cho-Tung Lee, Chun-Shing Ruan, Haihui Lam, Chi-Hang Department of Mechanical Engineering Hong Kong Polytechnic University Hong Kong School of Physics and Astronomy Cardiff University 5 The Parade Wales CardiffCF24 3AA United Kingdom School of Physics and Electronic Sciences Changsha University of Science and Technology Changsha410004 China Department of Physics Harbin Institute of Technology Shenzhen518055 China Department of Applied Physics Hong Kong Polytechnic University Hong Kong

The physics of glass has been a significant topic of interest for decades. Dynamical facilitation is widely believed to be an important characteristic of glassy dynamics, but the precise mechanism is still under debate. We propose a lattice model of glass called the facilitated random walk (FRW). Each particle performs continuous time random walk in the presence of its own random local kinetic constraints. The particles do not interact energetically. Instead, they interact kinetically with a hopping rate resampling rule under which motions of a particle can randomly perturb the local kinetic constraints of other particles. This dynamic interaction is reversible, following a rate restoration rule. A step-by-step reversal of the particle motions exactly restore the previous constraints, modeling randomness quenched in the configuration space of glass. The model exhibits stretched exponential relaxation and dynamical heterogeneity typical of glasses. Despite the lack of explicit facilitation rule, the FRW shows facilitation behaviors closely analogous to those of the kinetically constrained models (KCM). The FRW is a coarse-grained version of the distinguishable particle lattice model (DPLM) and this exemplifies that compatible defect and atomistic models can complement each other on the study of glass. © 2024, CC0.

关键词： Queueing theory

Time-Domain Topology Optimization of Power Dissipation in Dispersive Dielectric and Plasmonic Nanostructures

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arXiv 2024年

作者： Gedeon, Johannes Allayarov, Izzatjon Lesina, Antonio Calà Hassan, Emadeldeen The Hannover Centre for Optical Technologies The Institute for Transport and Automation Technology Faculty of Mechanical Engineering The Cluster of Excellence PhoenixD Leibniz University Hannover Hannover30167 Germany The Department of Applied Physics and Electronics Umeå University UmeåSE-901 87 Sweden

We present a density-based topology optimization scheme for locally optimizing the electric power dissipation in nanostructures made of lossy dispersive materials. By using the complex-conjugate pole-residue (CCPR) model, we can accurately model any linear materials’ dispersion without limiting to specific material classes. We incorporate the CCPR model via auxiliary differential equations (ADE) into Maxwell’s equations in the time domain, and formulate a gradient-based topology optimization problem to optimize the dissipation over a broad spectrum of frequencies. To estimate the objective function gradient, we use the adjoint field method, and explain the discretization and integration of the adjoint system into the finite-difference time-domain (FDTD) framework. Our method is demonstrated using the example of topology optimized spherical nanoparticles made of Gold and Silicon with an enhanced absorption efficiency in the visible-ultraviolet spectral range. In this context, a detailed analysis of the challenges of topology optimization of plasmonic materials associated with a density-based approach is given. © 2024, CC BY.

关键词： Silicon

Integrable Fractional Modified Korteweg-de Vries, Sine-Gordon, and Sinh-Gordon Equations

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arXiv 2022年

作者： Ablowitz, Mark J. Been, Joel B. Carr, Lincoln D. Department of Applied Mathematics University of Colorado BoulderCO United States Department of Applied Mathematics and Statistics Department of Physics Colorado School of Mines GoldenCO United States Quantum Engineering Program Department of Applied Mathematics and Statistics Department of Physics Colorado School of Mines GoldenCO United States

The inverse scattering transform allows explicit construction of solutions to many physically significant nonlinear wave equations. Notably, this method can be extended to fractional nonlinear evolution equations characterized by anomalous dispersion using completeness of suitable eigenfunctions of the associated linear scattering problem. In anomalous diffusion, the mean squared displacement is proportional to tα, α > 0, while in anomalous dispersion, the speed of localized waves is proportional to Aα, where A is the amplitude of the wave. Fractional extensions of the modified Korteweg-deVries (mKdV), sine-Gordon (sineG) and sinh-Gordon (sinhG) and associated hierarchies are obtained. Using symmetries present in the linear scattering problem, these equations can be connected with a scalar family of nonlinear evolution equations of which fractional mKdV (fmKdV), fractional sineG (fsineG), and fractional sinhG (fsinhG) are special cases. Completeness of solutions to the scalar problem is obtained and, from this, the nonlinear evolution equation is characterized in terms of a spectral expansion. In particular, fmKdV, fsineG, and fsinhG are explicitly written. One-soliton solutions are derived for fmKdV and fsineG using the inverse scattering transform and these solitons are shown to exhibit anomalous dispersion. © 2022, CC BY.

关键词： Dispersion (waves)

Characteristic nanoscale deformation on a large-area coherent graphite moiré pattern

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Physical Review B 2023年第16期107卷 L161402-L161402页

作者： N. Sarkar P. R. Bandaru R. C. Dynes Department of Mechanical Engineering University of California San Diego La Jolla California 92093-0411 USA Program in Materials Science University of California San Diego La Jolla California 92093-0411 USA Department of Physics University of California San Diego La Jolla California 92093-0411 USA

Highly oriented pyrolytic graphite may be the only known monatomic crystal with the ability to host naturally formed moiré patterns on its cleaved surfaces, which are coherent over micrometer scales and with discrete sets of twist angles of fixed periodicity. Such an aspect is in marked contrast to twisted bilayer graphene and other multilayered systems, where the long-range coherence of the moiré is not easily maintained due to twist angle disorder. We investigate the electronic and mechanical response of coherent graphite moiré patterns through inducing external strain from scanning tunneling microscopy tip-induced deformation. Consequently, unique anisotropic mechanical characteristics are revealed. For example, a lateral widening of one-dimensional domain walls (DWs) bridging Bernal (ABA) and rhombohedral (ABC) stacking domains (A, B, and C refer to the atomic layer positioning), was indicated. Further, in situ tunneling spectroscopy as a function of the deformation indicated a tendency towards increased electrical conductance, which may be associated with a higher density of electronic states, and the consequent flattening of the electronic energy band dispersion. Such features were probed across the DWs, with implications for strain-induced electronic modulation of the moiré characteristics.

关键词： Twisted bilayer graphene Scanning tunneling spectroscopy Strain engineering

Coddora: CO2-Based Occupancy Detection Model Trained via Domain Randomization

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Coddora: CO2-Based Occupancy Detection Model Trained via Dom...

International Joint Conference on Neural Networks (IJCNN)

作者： Manuel Weber Farzan Banihashemi Davor Stjelja Peter Mandl Ruben Mayer Hans-Arno Jacobsen Department of Computer Science and Mathematics Munich University of Applied Sciences (HM) Munich Germany Chair of Energy Efficient and Sustainable Design and Building Technical University of Munich Germany Department of Mechanical Engineering Aalto University Espoo Finland Faculty of Mathematics Physics and Computer Science University of Bayreuth Germany Department of Electrical and Computer Engineering University of Toronto Canada

ISBN: (数字)9798350359312

ISBN: (纸本)9798350359329

Information about human presence in indoor spaces is crucial for building energy optimization. While there has been a considerable amount of research on using neural networks to automatically detect occupancy from CO2 sensors, their application in practice is limited due to the scarcity of labeled training data. In this paper, we propose Coddora, an off-the-shelf deep learning model pretrained on data from randomized room simulations. Coddora enables quick adaptation to real-world rooms, requiring only minimal data collection. Our contribution includes two model variants for application via fine-tuning or zero-shot classifying, as well as the synthetic dataset providing data from simulations with 100,000 room models.

关键词： Training Adaptation models Accuracy Buildings Neural networks Transfer learning Training data