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Spin waves in magnetic Weyl semimetals

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Science China(Physics,Mechanics & Astronomy) 2021年第1期64卷 1-2页

作者： xincheng xie School of Physics Peking UniversityBeijing100871China

Intrinsic magnetic topological materials,namely the stoichiometric magnetic compounds possessing both inherent magnetic order and topological electronic states,have attracted tremendous interest in the research of condensed matter physics and materials science[1].Such materials not only bring new opportunities to realize many exotic topological phenomena under time-reversal symmetry breaking,but also show great potential in applications of quantum technology[2].

关键词： topological magnetic symmetry

Effective spin dephasing mechanism in confined two-dimensional topological insulators

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Science China(Physics,Mechanics & Astronomy) 2016年第7期59卷 70-75页

作者： JunJie Qi HaiWen Liu Hua Jiang xincheng xie Institute of Physics Chinese Academy of Sciences Beijing 100190 China Center for Advanced Quantum Studies Department of Physics Beijing Normal University Beijing 100875 China College of Physics optoelectronics and Energy Soochow University Suzhou 215006 China International Center for Quantum Materials and School of Physics Peking University Beijing 100871 China Collaborative Innovation Center of Quantum Matter Beijing 100871 China

A Kramers pair of helical edge states in quantum spin Hall effect(QSHE) is robust against normal dephasing but not robust to spin dephasing. In our work, we provide an effective spin dephasing mechanism in the puddles of two-dimensional(2D) QSHE, which is simulated as quantum dots modeled by 2D massive Dirac Hamiltonian. We demonstrate that the spin dephasing effect can originate from the combination of the Rashba spin-orbit coupling and electron-phonon interaction, which gives rise to inelastic backscattering in edge states within the topological insulator quantum dots, although the time-reversal symmetry is preserved throughout. Finally,we discuss the tunneling between extended helical edge states and local edge states in the QSH quantum dots, which leads to backscattering in the extended edge states. These results can explain the more robust edge transport in In As/Ga Sb QSH systems.

关键词：量子自旋退相干绝缘体二维拓扑机制电子-声子相互作用时间反演对称性

Evolution of Berry curvature and reentrant quantum anomalous Hall effect in an intrinsic magnetic topological insulator

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Science China(Physics,Mechanics & Astronomy) 2021年第12期64卷 138-143页

作者： Chui-Zhen Chen Junjie Qi Dong-Hui Xu xincheng xie Institute for Advanced Study and School of Physical Science and Technology Soochow UniversitySuzhou 215006China Beijing Academy of Quantum Information Sciences Beijing 100193China Department of Physics Hubei UniversityWuhan 430062China International Center for Quantum Materials School of PhysicsPeking UniversityBeijing 100871China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of SciencesBeijing 100190China

Recently, the magnetic topological insulator(TI) MnBi2Te4 emerged as a competitive platform to realize quantum anomalous Hall(QAH) states. We report a Berry curvature splitting mechanism to realize the QAH effect in the disordered magnetic TI multilayers when switching from an antiferromagnetic order to a ferromagnetic order. We reveal that the splitting of spin-resolved Berry curvature, originating from the separation of the critical points during the magnetic switching, can give rise to a QAH insulator. We present a global phase diagram, and also provide a phenomenological picture to elucidate the Berry curvature splitting mechanism by the evolution of topological charges. At last, we predict that the Berry curvature splitting mechanism will lead to a reentrant QAH effect, which can be detected by tuning the gate voltage. Our theory will be instructive for the studies of the QAH effect in MnBi2Te4 in future experiments.

关键词： quantum anomalous Hall effect Berry curvature disorder localization

Doubled Moiré fat bands in double-twisted few-layer graphite

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Science China(Physics,Mechanics & Astronomy) 2023年第2期66卷 95-101页

作者： Zhen Ma Shuai Li Ming Lu Dong-Hui Xu Jin-Hua Gao xincheng xie School of Physics Wuhan National High Magnetic Field CenterHuazhong University of Science and TechnologyWuhan 430074China Beijing Academyof Quantum Information Sciences Beijing100193China International Center for Quantum Materials School of PhysicsPeking UniversityBeijing 100871China Department of Physics and Chongqing Key Laboratory for Strongly Coupled Physics Chongqing UniversityChongqing 400044China Center of Quantum Materials and Devices Chongqing UniversityChongqing 400044China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of SciencesBeijing 100190China

We study the electronic structure of double-twisted few-layer graphite(DTFLG),which consists of three few-layer graphites(FLGs),i.e.,an ABA-stacked graphene multilayer,stacked with two twist angles.We consider two categories of DTFLG,the alternately and chirally twisted cases,according to the rotation direction of the two twist angles.We show that,once the middle FLG of DTFLG is not thinner than the trilayer,both types of DTFLG can remarkably host two pairs of degenerate Moire flat bands(MFBs) at EF,twice that of the magic angle twisted bilayer graphene(TBG).The doubled MFBs of DTFLG lead to a doubled density of states(DOS) at the Fermi level EF,which implies much stronger correlation effects than TBG.The degeneracy of MFBs can be lifted by a perpendicular electric field,and the isolated MFBs have a nonzero valley Chern number.We also reveal the peculiar wave function patterns of the MFB s in DTFLG.Our results establish a new family of Moire systems that have a much higher DOS at EFand thus possibly much stronger correlation effects.

关键词： twisted bands doubled

Minimal setup for non-Abelian braiding of Majorana zero modes

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Science China(Physics,Mechanics & Astronomy) 2021年第11期64卷 127-132页

作者： Jie Liu Wenqin Chen Ming Gong Yijia Wu xincheng xie Ministry of Education Key Laboratory for Non-Equilibrium Synthesis and Modulation of Condensed Matter School of PhysicsXi’an Jiaotong UniversityXi’an 710049China International Center for Quantum Materials School of PhysicsPeking UniversityBeijing 100871China Beijing Academy of Quantum Information Sciences Beijing 100193China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of SciencesBeijing 100190China

Braiding Majorana zero modes(MZMs)is the key procedure toward topological quantum computation.However,the complexity of the braiding manipulation hinders its experimental realization.Here we propose an experimental setup consisting of MZMs and a quantum dot state which can substantially simplify the braiding protocol of MZMs.Such braiding scheme,corresponding to a specific closed loop in the parameter space,is quite universal and can be realized in various platforms.Moreover,the braiding results can be measured and manifested through electric current,providing a simple and novel way to detect the non-Abelian statistics of MZMs.

关键词： non-Abelian statistics geometric phase Majorana zero modes

Magnetic flux control of chiral Majorana edge modes in topological superconductor

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Science China(Physics,Mechanics & Astronomy) 2018年第12期61卷 89-94页

作者： Yan-Feng Zhou Zhe Hou Peng Lv xincheng xie Qing-Feng Sun International Center for Quantum Materials School of PhysicsPeking UniversityBeijing 100871China Collaborative Innovation Center of Quantum Matter Beijing 100871China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of SciencesBeijing 100190China

We study the transport of chiral Majorana edge modes(CMEMs) in a hybrid quantum anomalous Hall insulator-topological superconductor(QAHI-TSC) system in which the TSC region contains a Josephson junction and a cavity. The Josephson junction undergoes a topological transition when the magnetic flux through the cavity passes through half-integer multiples of magnetic flux quantum. For the trivial phase, the CMEMs transmit along the QAHI-TSC interface as without magnetic flux. However, for the nontrivial phase, a zero-energy Majorana state appears in the cavity, leading to that a CMEM can resonantly tunnel through the Majorana state to a different CMEM. These findings may provide a feasible scheme to control the transport of CMEMs by using the magnetic flux and the transport pattern can be customized by setting the size of the TSC.

关键词： Majorana fermions Josephson junction topological superconductor non-equilibrium Green's function

Precision measurement physics:physics that precision matters

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National Science Review 2020年第12期7卷 1795-1795页

作者： Mingsheng Zhan xincheng xie Innovation Academy for Precision Measurement Science and Technology Chinese Academy of Sciences School of Physics Peking University

Without measurement,there would be no science.Modern science is established and developed in the process of hypothesis–test–model–theory cycle.Physics and measurement are inseparable.Precision measurement refers to the use of advanced technology and methods to pursue high accuracy under the existing physical framework.Precision measurement physics is to test the range of existing physics in a higher precision and try to find out the limit of the frame so as to discover new physics.

关键词：

Current noises in a topological Josephson junction

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Science China(Physics,Mechanics & Astronomy) 2018年第9期61卷 75-81页

作者： Yu-Hang Li Jie Liu JunTao Song Hua Jiang Qing-Feng Sun xincheng xie International Center for Quantum Materials School of Physics Peking University Beijing 100871 China Department of Applied Physics School of Science Xi'an Jiaotong University Xi'an 710049 China Department of Physics and Hebei Advanced Thin Film Laboratory Hebei Normal University Shijiazhuang 050024 China College of Physics Optoelectronics and Energy Soochow University Suzhou 215006 China Collaborative Innovation Center of Quantum Matter Beijing 100871 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing 100190 China

We study the transport properties of a superconductor-quantum spin Hall insulator-superconductor Josephson junction both in the absence and in the presence of a DC bias voltage. As the system is predicted to host Majorana fermions at its interfaces,the Andreev bond states are supposed to exhibit a distinct 4π periodicity in the superconducting phase difference, namely the fractional Josephson effect. Using the non-equilibrium Green's function method, we calculate the current and the related current noise based on a tight-binding Hamiltonian. Our direct results show that the fractional Josephson effect can not be seen in equilibrium junctions. While in non-equilibrium junctions, this effect can be confirmed by the multiple Andreev reflections induced peaks of the non-equilibrium noise, which appear at discrete frequencies ω = ne V with n being an integer number.

关键词： Josephson 连接噪音 Hamiltonian 拓扑非平衡超导体计算电流

A new type of Andreev reflection

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Science China(Physics,Mechanics & Astronomy) 2021年第6期64卷 1-1页

作者： xincheng xie School of Physics Peking UniversityBeijing 100871China

Andreev reflection (AR) [1] refers to a peculiar quasiparticle reflection process that takes place at the interface between a normal metal and a superconductor.Specifically,an electron impinging from the normal metal is reflected back as a hole,which effectively describes that two electrons in the normal metal penetrate into the superconductor and form a Cooper pair.AR dominates the electron transport below the superconducting gap in the superconductor junctions,which is an important experimental approach for the detection of various properties of electronic systems,such as the pairing symmetry of the unconventional superconductors,the spin polarization of the itinerant electrons and most recently,Majorana zero mode in topological systems.

关键词： superconductor reflection symmetry