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Decays of Majorana or Andreev oscillations induced by steplike spin-orbit coupling

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arXiv 2018年

作者： Cao, Zhan Zhang, Hao Lü, Hai-Feng He, Wan-Xiu Lu, Hai-Zhou Xie, X.C. Shenzhen Institute for Quantum Science and Engineering Department of Physics Southern University of Science and Technology Shenzhen518055 China School of Physics Southeast University Nanjing211189 China Peng Cheng Laboratory Shenzhen518055 China Shenzhen Key Laboratory of Quantum Science and Engineering Shenzhen518055 China State Key Laboratory of Low Dimensional Quantum Physics Department of Physics Tsinghua University Beijing100084 China Beijing Academy of Quantum Information Sciences Beijing100193 China School of Physics University of Electronic Science and Technology of China Chengdu610054 China Center for Interdisciplinary Studies and Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education Lanzhou University Lanzhou730000 China International Center for Quantum Materials School of Physics Peking University Beijing100871 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing100190 China

The Majorana zero mode in the semiconductor-superconductor nanowire is one of the promising candidates for topological quantum computing. Recently, in islands of nanowires, subgap-state energies have been experimentally observed to oscillate as a function of the magnetic field, showing a signature of overlapped Majorana bound states. However, the oscillation amplitude either dies away after an overshoot or decays, sharply opposite to the theoretically predicted enhanced oscillations for Majorana bound states. We reveal that a steplike distribution of spin-orbit coupling in realistic devices can induce the decaying Majorana oscillations, resulting from the coupling-induced energy repulsion between the quasiparticle spectra on the two sides of the step. This steplike spin-orbit coupling can also lead to decaying oscillations in the spectrum of the Andreev bound states. For Coulomb-blockade peaks mediated by the Majorana bound states, the peak spacings have been predicted to correlate with peak heights by a π/2 phase shift, which was ambiguous in recent experiments and may be explained by the steplike spin-orbit coupling. Our work will inspire more works to reexamine effects of the nonuniform spin-orbit coupling, which is generally present in experimental devices. Copyright © 2018, The Authors. All rights reserved.

关键词： Nanowires

πγ→ππ transition and the ρ radiative decay width from lattice QCD

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Physical Review D 2018年第7期98卷 074502-074502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 Street 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 report a lattice QCD determination of the πγ→ππ transition amplitude for the P-wave, I=1 two-pion final state, as a function of the photon virtuality and ππ invariant mass. The calculation was performed with 2+1 flavors of clover fermions at a pion mass of approximately 320 MeV, on a 323×96 lattice with L≈3.6 fm. We construct the necessary correlation functions using a combination of smeared forward, sequential and stochastic propagators, and determine the finite-volume matrix elements for all ππ momenta up to |P→|=32πL and all associated irreducible representations. In the mapping of the finite-volume to infinite-volume matrix elements using the Lellouch-Lüscher factor, we consider two different parametrizations of the ππ scattering phase shift. We fit the q2 and s dependence of the infinite-volume transition amplitude in a model-independent way using series expansions, and compare multiple different truncations of this series. Through analytic continuation to the ρ resonance pole, we also determine the πγ→ρ resonant transition form factor and the ρ meson photocoupling, and obtain |Gρπγ|=0.0802(32)(20).

关键词： Hadron-hadron interactions Leptonic, semileptonic & radiative decays Pions Vector mesons Form factors Lattice QCD

Towards the P-wave nucleon-pion scattering amplitude in the ∆(1232) channel 36

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Towards the P-wave nucleon-pion scattering amplitude in the ...

36th Annual International Symposium on Lattice Field Theory, LATTICE 2018

作者： Paul, Srijit Silvi, Giorgio Alexandrou, Constantia Koutsou, Giannis Krieg, Stefan Leskovec, Luka Meinel, Stefan Negele, John W. Petschlies, Marcus Pochinsky, Andrew Rendon, Gumaro Syritsyn, Sergey Computation-based Science and Technology Research Center Cyprus Institute 20 Kavafi Str. Nicosia2121 Cyprus Faculty of Mathematics und Natural Sciences University of Wuppertal Wuppertal42119 Germany Department of Physics University of Cyprus POB 20537 Nicosia1678 Cyprus Institute for Advanced Simulation Forschungszentrum Jülich GmbH Jülich52425 Germany Theory Center Jefferson Lab Newport NewsVA23606 United States Department of Physics University of Arizona TucsonAZ85721 United States RIKEN BNL Research Center Brookhaven National Laboratory UptonNY11973 United States Center for Theoretical Physics Massachusetts Institute of Technology CambridgeMA02139 United States Helmholtz-Institut für Strahlen- und Kernphysik University of Bonn Bonn53115 Germany Department of Physics and Astronomy Stony Brook University Stony BrookNY11794 United States

We use lattice QCD and the Lüscher method to study elastic pion-nucleon scattering in the isospin I = 3/2 channel, which couples to the ∆(1232) resonance. Our Nf = 2 + 1 flavor lattice setup features a pion mass of mπ ≈ 250 MeV, such that the strong decay channel ∆ → πN is close to the threshold. We present our method for constructing the required lattice correlation functions from single- and two-hadron interpolating fields and their projection to irreducible representations of the relevant symmetry group of the lattice. We show preliminary results for the energy spectra in selected moving frames and irreducible representations, and extract the scattering phase shifts. Using a Breit-Wigner fit, we also determine the resonance mass m∆ and the g∆−πN coupling. © Copyright owned by the author(s) under the terms of the Creative Commons.

关键词： Hadrons

Itinerant quantum critical point with frustration and a non-Fermi liquid

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Physical Review B 2018年第4期98卷 045116-045116页

作者： Zi Hong Liu Xiao Yan Xu Yang Qi Kai Sun Zi Yang Meng Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 China School of Physical Sciences University of Chinese Academy of Sciences Beijing 100190 China Department of Physics Hong Kong University of Science and Technology Clear Water Bay Hong Kong China Department of Physics Fudan University Shanghai 200433 China Department of Physics Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA Department of Physics University of Michigan Ann Arbor Michigan 48109 USA CAS Center of Excellence in Topological Quantum Computation and School of Physical Sciences University of Chinese Academy of Sciences Beijing 100190 China

Employing the self-learning quantum Monte Carlo algorithm, we investigate the frustrated transverse-field triangle-lattice Ising model coupled to a Fermi surface. Without fermions, the spin degrees of freedom undergo a second-order quantum phase transition between paramagnetic and clock-ordered phases. This quantum critical point (QCP) has an emergent U(1) symmetry and thus belongs to the (2+1)D XY universality class. In the presence of fermions, spin fluctuations introduce effective interactions among fermions and distort the bare Fermi surface towards an interacting one with hot spots and Fermi pockets. Near the QCP, non-Fermi-liquid behaviors are observed at the hot spots, and the QCP is rendered into a different universality with Hertz-Millis–type exponents. The detailed properties of this QCP and possibly related experimental systems are also discussed.

关键词： Critical exponents Frustrated magnetism Quantum phase transitions Machine learning Quantum Monte Carlo

Quantum Spin Liquid with Even Ising Gauge Field Structure on Kagome Lattice

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Physical Review Letters 2018年第5期121卷 057202-057202页

作者： Yan-Cheng Wang Xue-Feng Zhang (张学锋) Frank Pollmann Meng Cheng Zi Yang Meng Beijing National Laboratory of Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 People’s Republic of China School of Physical Science and Technology China University of Mining and Technology Xuzhou Jiangsu 221116 People’s Republic of China Department of Physics Chongqing University Chongqing 401331 People’s Republic of China Max-Planck-Institute for the Physics of Complex Systems 01187 Dresden Germany Department of Physics Technical University of Munich 85748 Garching Germany Department of Physics Yale University New Haven Connecticut 06520-8120 USA CAS Center of Excellence in Topological Quantum Computation and School of Physical Sciences University of Chinese Academy of Sciences Beijing 100190 People’s Republic of China

Employing large-scale quantum Monte Carlo simulations, we study the extended XXZ model on the kagome lattice. A Z2 quantum spin liquid phase with effective even Ising gauge field structure emerges from the delicate balance among three symmetry-breaking phases including stripe solid, staggered solid, and ferromagnet. This Z2 spin liquid is stabilized by an extended interaction related to the Rokhsar-Kivelson potential in the quantum dimer model limit. The phase transitions from the staggered solid to a spin liquid or ferromagnet are found to be first order and so is the transition between the stripe solid and ferromagnet. However, the transition between a spin liquid and ferromagnet is found to be continuous and belongs to the 3D XY* universality class associated with the condensation of spinons. The transition between a spin liquid and stripe solid appears to be continuous and associated with the condensation of visons.

关键词： Anyons Quantum spin liquid Ising model Quantum Monte Carlo

Uncover Topology by Quantum Quench Dynamics

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Physical Review Letters 2018年第25期121卷 250403-250403页

作者： Wei Sun Chang-Rui Yi Bao-Zong Wang Wei-Wei Zhang Barry C. Sanders Xiao-Tian Xu Zong-Yao Wang Joerg Schmiedmayer Youjin Deng Xiong-Jun Liu Shuai Chen Jian-Wei Pan Shanghai Branch National Laboratory for Physical Sciences at Microscale and Department of Modern Physics University of Science and Technology of China Shanghai 201315 China Chinese Academy of Sciences Center for Excellence: Quantum Information and Quantum Physics University of Science and Technology of China Hefei Anhui 230326 China CAS-Alibaba Lab for Quantum Computation Shanghai 201315 China International Center for Quantum Materials School of Physics Peking University Beijing 100871 China Collaborative Innovation Center of Quantum Matter Beijing 100871 China Centre for Engineered Quantum Systems School of Physics The University of Sydney Sydney New South Wales 2006 Australia Institute for Quantum Science and Technology University of Calgary Calgary Alberta T2N 1N4 Canada Program in Quantum Information Science Canadian Institute for Advanced Research Toronto Ontario M5G 1Z8 Canada Vienna Center for Quantum Science and Technology Atominstitut TU Wien Stadionallee 2 1020 Vienna Austria

Topological quantum states are characterized by nonlocal invariants. We present a new dynamical approach for ultracold-atom systems to uncover their band topology, and we provide solid evidence to demonstrate its experimental advantages. After quenching a two-dimensional (2D) Chern band, realized in an ultracold Rb87 gas from a trivial to a topological parameter regime, we observe an emerging ring structure in the spin dynamics during the unitary evolution, which uniquely corresponds to the Chern number for the postquench band. By extracting 2D bulk topology from the 1D ring pattern, our scheme displays simplicity and is insensitive to perturbations. This insensitivity enables a high-precision determination of the full phase diagram for the system’s band topology.

关键词： Spin-orbit coupling Synthetic gauge fields Bose gases

Optical Stark Effect of a Single Defect on TiO2(110) Surface

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arXiv 2018年

作者： Sun, Lihuan Dong, Anning Li, Jianmei Hao, Dong Tang, Xiangqian Yan, Shichao Guo, Yang Shan, Xinyan Lu, Xinghua 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 School of Physical Science and Technology ShanghaiTech University Shanghai201210 China Center for Excellence in Topological Quantum Computation Chinese Academy of Sciences Beijing100190 China

Probing optical Stark effect at the single-molecule or atomic scale is crucial for understanding many photo-induced chemical and physical processes on surfaces. Here we report a study about optical Stark effect of single atomic defects on TiO2(110) surface with photo-assisted scanning tunneling spectroscopy. When a laser is coupled into the tunneling junction, the mid-gap state of OH-O2 defects changes remarkably in the differential conductance spectra. As laser power gradually increases, the energy of the mid-gap state shifts away from the Fermi level with increase in intensity and broadening of peak width. The observation can be explained as optical Stark effect with the Autler-Townes formula. This large optical Stark effect is due to the tip-enhancement and the strong dipole moment in the transient charged state during electron tunneling. Our study provides new aspects in exploring electron-photon interactions at the microscopic scale. Copyright © 2018, The Authors. All rights reserved.

关键词： Electron tunneling

Quantum coherence across bosonic superconductor-anomalous metal-insulator transitions

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arXiv 2019年

作者： Yang, Chao Liu, Yi Wang, Yang Feng, Liu He, Qianmei Sun, Jian Tang, Yue Wu, Chunchun Xiong, Jie Zhang, Wanli Lin, Xi Yao, Hong Liu, Haiwen Fernandes, Gustavo Xu, Jimmy Valles, James M. Wang, Jian Li, Yanrong State Key Laboratory of Electronic Thin Films and Integrated Devices University of Electronic Science and Technology of China Chengdu610054 China International Center for Quantum Materials School of Physics Peking University Beijing100871 China Collaborative Innovation Center of Quantum Matter Beijing100871 China Institute for Advanced Study Tsinghua University Beijing100084 China State Key Laboratory of Low Dimensional Quantum Physics Tsinghua University Beijing100084 China Center for Advanced Quantum Studies Department of Physics Beijing Normal University Beijing100875 China School of Engineering Brown University 182 Hope Street ProvidenceRI02912 United States Department of Physics Brown University 182 Hope Street ProvidenceRI02912 United States CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing100190 China Beijing Academy of Quantum Information Sciences West Bld. #3 No. 10 Xibeiwang East Rd. Haidian District Beijing100193 China

After decades of explorations, suffering from low critical temperature and subtle nature, whether a metallic ground state exists in a two-dimensional system beyond Anderson localization is still a mystery. Supremely, phase coherence could be the key that unlocks its intriguing nature. This work reveals how quantum phase coherence evolves across bosonic superconductor-metal-insulator transitions via magneto-conductance quantum oscillations in high-Tc superconducting films. A robust intervening anomalous metallic state characterized by both resistance and oscillation amplitude saturations in the low temperature regime is detected. By contrast, with decreasing temperature the oscillation amplitude monotonically grows on the superconducting side, but decreases at low temperatures on the insulating side. It suggests that the saturation of phase coherence plays a prominent role in the formation of this anomalous metallic state. Copyright © 2019, The Authors. All rights reserved.

关键词： Bosons

Accelerated discovery of two-dimensional optoelectronic octahedral oxyhalides via high-throughput ab initio calculations and machine learning

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arXiv 2019年

作者： Ma, Xing-Yu Lewis, James P. Yan, Qing-Bo Su, Gang School of Physical Sciences University of Chinese Academy of Sciences Beijing100049 China Department of Physics and Astronomy West Virginia University MorgantownWV26506-6315 United States State Key Laboratory of Coal Conversion Institute of Coal Chemistry Chinese Academy of Sciences Taiyuan Shanxi030001 China Beijing Advanced Innovation Center for Materials Genome Engineering Beijing Information S&T University Beijing101400 China Center of Materials Science and Optoelectronics Engineering College of Materials Science and Optoelectronic Technology University of Chinese Academy of Sciences Beijing100049 China Kavli Institute for Theoretical Sciences CAS Center of Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing100190 China

Traditional trial-and-error methods are obstacles for large-scale searching of new optoelectronic materials. Here, we introduce a method combining high-throughput ab initio calculations and machine-learning approaches to predict two-dimensional octahedral oxyhalides with improved optoelectronic properties. We develop an effective machine-learning model based on an expansive dataset generated from density functional calculations including the geometric and electronic properties of 300 two-dimensional octahedral oxyhalides. Our model accelerates the screening of potential optoelectronic materials of 5,000 two-dimensional octahedral oxyhalides. The distorted stacked octahedral factors proposed in our model play essential roles in the machine-learning prediction. Several potential two-dimensional optoelectronic octahedral oxyhalides with moderate band gaps, high electron mobilities, and ultrahigh absorbance coefficients are successfully hypothesized. © 2019, CC BY-NC-SA.

关键词： Optoelectronic devices