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Tunable Mode Coupling in Nanocontact Spin-Torque Oscillators

Physical Review Applied 2017年第1期8卷 014034-014034页

作者： Steven S.-L. Zhang Ezio Iacocca Olle Heinonen Department of Physics and Astronomy University of Missouri Columbia Missouri 65211 USA Material Science Division Argonne National Laboratory Lemont Illinois 60439 USA Department of Applied Mathematics University of Colorado Boulder Colorado 80309-0526 USA Department of Physics Division for Theoretical Physics Chalmers University of Technology 412 96 Gothenburg Sweden Northwestern-Argonne Institute of Science and Technology 2145 Sheridan Road Evanston Illinois 60208 USA Computation Institute The University of Chicago 5735 South Ellis Avenue Chicago Illinois 60637 USA

Recent experiments on spin-torque oscillators have revealed interactions between multiple magnetodynamic modes, including mode coexistence, mode hopping, and temperature-driven crossover between modes. The initial multimode theory indicates that a linear coupling between several dominant modes, arising from the interaction of the subdynamic system with a magnon bath, plays an essential role in the generation of various multimode behaviors, such as mode hopping and mode coexistence. In this work, we derive a set of rate equations to describe the dynamics of coupled magnetodynamic modes in a nanocontact spin-torque oscillator. Expressions for both linear and nonlinear coupling terms are obtained, which allow us to analyze the dependence of the coupled dynamic behaviors of modes on external experimental conditions as well as intrinsic magnetic properties. For a minimal two-mode system, we further map the energy and phase difference of the two modes onto a two-dimensional phase space and demonstrate in the phase portraits how the manifolds of periodic orbits and fixed points vary with an external magnetic field as well as with the temperature.

关键词： Spin transfer torque Spin waves Spintronics Spin valves Landau-Lifschitz-Gilbert equation

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Kπ scattering and the K∗(892) resonance in 2+1 flavor QCD

arXiv

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arXiv 2018年

作者： Rendon, Gumaro Leskovec, Luka Meinel, Stefan Negele, John W. Paul, Srijit Petschlies, Marcus Pochinsky, Andrew Silvi, Giorgio Syritsyn, Sergey Department of Physics University of Arizona TucsonAZ85721 United States Theory Center Jefferson Lab Newport NewsVA23606 United States Computation-based Science and Technology Research Center Cyprus Institute Nicosia2121 Cyprus RIKEN BNL Research Center Brookhaven National Laboratory UptonNY11973 United States Center for Theoretical Physics Massachusetts Institute of Technology CambridgeMA02139 United States Department of Mathematics and Natural Sciences University of Wuppertal WuppertalD-42119 Germany Helmholtz-Institut für Strahlen- und Kernphysik University of Bonn BonnD-53115 Germany Department of Physics and Astronomy Stony Brook University Stony BrookNY11794 United States Forschungszentrum Jülich GmbH Jülich Supercomputing Centre Jülich52425 Germany

In this project, we will compute the form factors relevant for B → K∗(→ Kπ)`+`− decays. To map the finite-volume matrix elements computed on the lattice to the infinite-volume B → Kπ matrix elements, the Kπ scattering amplitude needs to be determined using Lüscher’s method. Here we present preliminary results from our calculations with 2 + 1 flavors of dynamical clover fermions. We extract the P-wave scattering phase shifts and determine the K∗ resonance mass and the K∗Kπ coupling for two different ensembles with pion masses of 317(2) and 178(2) MeV. Copyright © 2018, The Authors. All rights reserved.

关键词： Seismic waves

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Front Cover: The Synthesis and Optoelectronic Applications for Tellurophene-Based Small Molecules and Polymers (ChemPhysChem 20/2019)

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ChemPhysChem 2019年第20期20卷 2577-2577页

作者： Xiaoxi Wu Lei Lv Lifang Hu Prof. Qinqin Shi Prof. Aidong Peng Prof. Hui Huang College of Materials Science and Opto-Electronic Technology & Center of Materials Science and Optoelectronics Engineering & CAS Center for Excellence in Topological Quantum Computation & CAS Key Laboratory of Vacuum Physics University of Chinese Academy of Sciences Beijing 100049 P. R. China Department of Chemical and Biochemical Engineering Technical University of Denmark Building 229 2800 Kgs. Lyngby. Sino-Danish College University of Chinese Academy of Sciences Beijing 100049 China.Sino-Danish center for Education and Research University of Chinese Academy of Sciences Beijing 100049 China

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Superconductivity: Pressure-Induced Metallization and Robust Superconductivity in Pristine 1T-SnSe2(Adv. Electron. Mater. 8/2018)

引用

Advanced Electronic Materials 2018年第8期4卷

作者： Yonghui Zhou Bowen Zhang Xuliang Chen Chuanchuan Gu Chao An Ying Zhou Kaiming Cai Yifang Yuan Chunhua Chen Hao Wu Ranran Zhang Changyong Park Yimin Xiong Xiuwen Zhang Kaiyou Wang Zhaorong Yang Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions High Magnetic Field Laboratory Chinese Academy of Sciences Hefei 230031 China University of Science and Technology of China Hefei 230026 China SKLSM Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 China Department of Physics and Laboratory of Material Physics Zhengzhou University Zhengzhou 450052 China HPCAT Geophysical Laboratory Carnegie Institution of Washington Argonne IL 60439 USA Collaborative Innovation Center of Advanced Microstructures Nanjing University Nanjing 210093 China College of Electronic Science and Technology Shenzhen University Shenzhen 518060 China College of Materials science & Opto-Electronic Technology and Center for Excellence in Topological Quantum Computation University of Chinese Academy of Science Beijing 100049 China Institute of Physical Science and Information Technology Anhui University Hefei 230601 China

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P-wave ππ scattering and the ρ resonance from lattice QCD

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Physical Review D 2017年第3期96卷 034525-034525页

作者： Constantia Alexandrou Luka Leskovec Stefan Meinel John Negele Srijit Paul Marcus Petschlies Andrew Pochinsky Gumaro Rendon Sergey Syritsyn Department of Physics University of Cyprus P.O. Box 20537 1678 Nicosia Cyprus Computation-based Science and Technology Research Center Cyprus Institute 20 Kavafi Str. 2121 Nicosia Cyprus Department of Physics University of Arizona Tucson Arizona 85721 USA RIKEN BNL Research Center Brookhaven National Laboratory Upton New York 11973 USA Center for Theoretical Physics Laboratory for Nuclear Science and Department of Physics Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA Helmholtz-Institut für Strahlen- und Kernphysik Rheinische Friedrich-Wilhelms-Universität Bonn Nußallee 14-16 D-53115 Bonn Germany Department of Physics and Astronomy Stony Brook University Stony Brook New York 11794 USA

We calculate the parameters describing elastic I=1, P-wave ππ scattering using lattice QCD with 2+1 flavors of clover fermions. Our calculation is performed with a pion mass of mπ≈320 MeV and a lattice size of L≈3.6 fm. We construct the two-point correlation matrices with both quark-antiquark and two-hadron interpolating fields using a combination of smeared forward, sequential and stochastic propagators. The spectra in all relevant irreducible representations for total momenta |P→|≤32πL are extracted with two alternative methods: a variational analysis as well as multiexponential matrix fits. We perform an analysis using Lüscher’s formalism for the energies below the inelastic thresholds, and investigate several phase shift models, including possible nonresonant contributions. We find that our data are well described by the minimal Breit-Wigner form, with no statistically significant nonresonant component. In determining the ρ resonance mass and coupling we compare two different approaches: fitting the individually extracted phase shifts versus fitting the t-matrix model directly to the energy spectrum. We find that both methods give consistent results, and at a pion mass of amπ=0.18295(36)stat obtain gρππ=5.69(13)stat(16)sys, amρ=0.4609(16)stat(14)sys, and amρ/amN=0.7476(38)stat(23)sys, where the first uncertainty is statistical and the second is the systematic uncertainty due to the choice of fit ranges.

关键词： Hadron-hadron interactions Hadronic decays Lattice QCD Lattice gauge theory Hadrons Light mesons Mesons Vector mesons Lattice field theory

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Self-sustained activity in balanced networks with low firing-rate

arXiv

引用

arXiv 2018年

作者： Borges, F.S. Protachevicz, P.R. Pena, R.F.O. Lameu, E.L. Matias, F.S. Higa, G.S.V. Kihara, A.H. Antonopoulos, C.G. Iarosz, K.C. de Pasquale, R. Roque, A.C. Batista, A.M. Ji, P. Center for Mathematics Computation and Cognition Federal University of ABC São Bernardo do Campo SP Brazil Institute of Physics University of São Paulo São Paulo SP Brazil Graduate in Science Program - Physics State University of Ponta Grossa PR Brazil Laboratory of Neural Systems Department of Physics University of São Paulo Ribeirão Preto SP Brazil National Institute for Space Research São José dos Campos SP Brazil Department of Physics Humboldt University Berlin Germany Cognitive Neuroimaging Unit CEA DRF/I2BM INSERM Université Paris-Sud Université Paris-Saclay Gif/YvetteF-91191 France Institute of Physics Federal University of Alagoas Maceió AL Brazil Department of Mathematical Sciences University of Essex Wivenhoe Park United Kingdom Potsdam Institute for Climate Impact Research Potsdam Germany Department of Physiology and Biophysics ICB University of São Paulo São Paulo SP Brazil Department of Mathematics and Statistics State University of Ponta Grossa Ponta Grossa PR Brazil Institute of Science and Technology for Brain-Inspired Intelligence Fudan University Shanghai China

The brain can display self-sustained activity (SSA), which is persistent firing of neurons in the absence of external stimuli. This spontaneous activity shows low neuronal firing rates and is observed in diverse in vitro and in vivo situations. In this work, we study the influence of excitatory/inhibitory balance, connection density, and network size on the self-sustained activity of a neuronal network model. We build a random network of adaptive exponential integrate-and-fire (AdEx) neuron models connected through inhibitory and excitatory chemical synapses. The AdEx model mimics several behaviours of biological neurons, such as spike initiation, adaptation, and bursting patterns. In an excitation/inhibition balanced state, if the mean connection degree (K) is fixed, the firing rate does not depend on the network size (N), whereas for fixed N, the firing rate decreases when K increases. However, for large K, SSA states can appear only for large N. We show the existence of SSA states with similar behaviours to those observed in experimental recordings, such as very low and irregular neuronal firing rates, and spike-train power spectra with slow fluctuations, only for balanced networks of large size. Copyright © 2018, The Authors. All rights reserved.

关键词： Neural networks

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Dynamics of topological excitations in a model quantum spin ice

arXiv

引用

arXiv 2017年

作者： Huang, Chun-Jiong Deng, Youjin Wan, Yuan Meng, Zi Yang Shanghai Branch National Laboratory for Physical Sciences at Microscale Department of Modern Physics University of Science and Technology of China Shanghai201315 China CAS Center for Excellence Synergetic Innovation Center in Quantum Information and Quantum Physics University of Science and Technology of China Hefei Anhui230026 China CAS-Alibaba Quantum Computing Laboratory Shanghai201315 China Perimeter Institute for Theoretical Physics WaterlooONN2L 2Y5 Canada Institute of Physics Chinese Academy of Sciences Beijing100190 China CAS Center of Excellence in Topological Quantum Computation School of Physical Sciences University of Chinese Academy of Sciences Beijing100190 China

We study the quantum spin dynamics of a frustrated XXZ model on a pyrochlore lattice by using large-scale quantum Monte Carlo simulation and stochastic analytic continuation. In the low-temperature quantum spin ice regime, we observe signatures of coherent photon and spinon excitations in the dynamic spin structure factor. As the temperature rises to the classical spin ice regime, the photon disappears from the dynamic spin structure factor, whereas the dynamics of the spinon remain coherent in a broad temperature window. Our results provide experimentally relevant, quantitative information for the ongoing pursuit of quantum spin ice materials. Copyright © 2017, The Authors. All rights reserved.

关键词： Monte Carlo methods

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Quantum state and process tomography via adaptive measurements

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science China(physics,Mechanics & Astronomy) 2016年第10期59卷 25-32页

作者： HengYan Wang WenQiang Zheng NengKun Yu KeRen Li DaWei Lu Tao Xin Carson Li ZhengFeng Ji David Kribs Bei Zeng XinHua Peng JiangFeng Du Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics University of Science and Technology of ChinaHefei 230026China Department of Applied Physics Zhejiang University of TechnologyHangzhou 310023China Institute for Quantum Computing University of WaterlooWaterloo N2L 3G1Canada 4Department of Mathematics&Statistics University of GuelphGuelph N1G 2W1Canada Centre for Quantum Computation&Intelligent Systems Faculty of Engineering and Information TechnologyUniversity of Technology SydneySydney NSW 2007Australia State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics Tsinghua UniversityBeijing 100084China Department of Physics University of GuelphGuelph N1G 2W1Canada State Key Laboratory of Computer Science Institute of SoftwareChinese Academy of SciencesBeijing 100190China Canadian Institute for Advanced Research Toronto M5G 1Z8Canada

We investigate quantum state tomography(QST) for pure states and quantum process tomography(QPT) for unitary channels via adaptive measurements. For a quantum system with a d-dimensional Hilbert space, we first propose an adaptive protocol where only 2d. 1 measurement outcomes are used to accomplish the QST for all pure states. This idea is then extended to study QPT for unitary channels, where an adaptive unitary process tomography(AUPT) protocol of d2+d.1measurement outcomes is constructed for any unitary channel. We experimentally implement the AUPT protocol in a 2-qubit nuclear magnetic resonance system. We examine the performance of the AUPT protocol when applied to Hadamard gate, T gate(/8 phase gate), and controlled-NOT gate,respectively, as these gates form the universal gate set for quantum information processing purpose. As a comparison, standard QPT is also implemented for each gate. Our experimental results show that the AUPT protocol that reconstructing unitary channels via adaptive measurements significantly reduce the number of experiments required by standard QPT without considerable loss of fidelity.

关键词： quantum tomography state reconstruction nuclear magnetic resonance

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Tunable mode coupling in nano-contact spin torque oscillators

arXiv

引用

arXiv 2017年

作者： Zhang, Steven S.-L. Iacocca, Ezio Heinonen, Olle Department of Physics and Astronomy University of Missouri ColumbiaMO65211 United States Material Science Division Argonne National Laboratory LemontIL60439 United States Department of Applied Mathematics University of Colorado BoulderCO80309-0526 United States Department of Physics Division for Theoretical Physics Chalmers University of Technology Gothenburg412 96 Sweden Northwestern-Argonne Institute of Science and Technology 2145 Sheridan Road EvanstonIL60208 United States Computation Institute University of Chicago 5735 S Ellis Ave ChicagoIL60637 United States

Recent experiments on spin torque oscillators have revealed interactions between multiple magnetodynamic modes, including mode-coexistence, mode-hopping, and temperature-driven cross-over between modes. Initial multimode theory has indicated that a linear coupling between several dominant modes, arising from the interaction of the subdynamic system with a magnon bath, plays an essential role in the generation of various multimode behaviors, such as mode hopping and mode coexistence. In this work, we derive a set of rate equations to describe the dynamics of coupled magnetodynamic modes in a nano-contact spin torque oscillator. Expressions for both linear and nonlinear coupling terms are obtained, which allow us to analyze the dependence of the coupled dynamic behaviors of modes on external experimental conditions as well as intrinsic magnetic properties. For a minimal two-mode system, we further map the energy and phase difference of the two modes onto a two-dimensional phase space, and demonstrate in the phase portraits, how the manifolds of periodic orbits and fixed points vary with external magnetic field as well as with temperature. Copyright © 2017, The Authors. All rights reserved.

关键词： Spin dynamics

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Evidence for majorana bound state in an iron-based superconductor

arXiv

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arXiv 2017年

作者： Wang, Dongfei Kong, Lingyuan Fan, Peng Chen, Hui Zhu, Shiyu Liu, Wenyao Cao, Lu Sun, Yujie Du, Shixuan Schneeloch, John Zhong, Ruidan Gu, Genda Fu, Liang Ding, Hong Gao, Hong-Jun Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing100190 China School of Physical Sciences University of Chinese Academy of Sciences Beijing100190 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing100190 China Collaborative Innovation Center of Quantum Matter Beijing100190 China Condensed Matter Physics and Materials Science Department Brookhaven National Laboratory UptonNY11973 United States Department of Physics Massachusetts Institute of Technology CambridgeMA02139 United States

The search for Majorana bound state (MBS) has recently emerged as one of the most active research areas in condensed matter physics, fueled by the prospect of using its non-Abelian statistics for robust quantum computation. A highly sought-after platform for MBS is two-dimensional topological superconductors, where MBS is predicted to exist as a zero-energy mode in the core of a vortex. A clear observation of MBS, however, is often hindered by the presence of additional low-lying bound states inside the vortex core. By using scanning tunneling microscope on the newly discovered superconducting Dirac surface state of iron-based superconductor FeTe1-xSex (x = 0.45, superconducting transition temperature Tc = 14.5 K), we clearly observe a sharp and non-split zero-bias peak inside a vortex core. Systematic studies of its evolution under different magnetic fields, temperatures, and tunneling barriers strongly suggest that this is the case of tunneling to a nearly pure MBS, separated from non-topological bound states which is moved away from the zero energy due to the high ratio between the superconducting gap and the Fermi energy in this material. This observation offers a new, robust platform for realizing and manipulating MBSs at a relatively high temperature. Copyright © 2017, The Authors. All rights reserved.

关键词： Iron-based Superconductors

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