We report the experimental investigation of the superconductor-metal quantum phase transition of the Eu O/KTa O3 interface.Around the transition,a divergence of the dynamical critical exponent is observed,which suppor...We report the experimental investigation of the superconductor-metal quantum phase transition of the Eu O/KTa O3 interface.Around the transition,a divergence of the dynamical critical exponent is observed,which supports the quantum Griffiths singularity in the Eu O/KTa O3 interface.The quantum Griffiths singularity could be attributed to large rare superconducting regions and quenched disorders at the interface.Our results could pave the way for studying the exotic superconducting properties at the Eu O/KTa O3 interface.展开更多
Majorana zero modes(MZMs)are the most intensively studied non-Abelian anyons.The Dirac fermion zero modes in topological insulators,which are symmetry-protected doubling of MZMs under fermion number conservation,offer...Majorana zero modes(MZMs)are the most intensively studied non-Abelian anyons.The Dirac fermion zero modes in topological insulators,which are symmetry-protected doubling of MZMs under fermion number conservation,offer an alternative approach to explore non-Abelian anyons.However,a unified model that elucidates the braiding statistics of these types of topological zero modes remains absent.We show that the minimal Kitaev chain model beyond fine-tuning regime provides a unified characterization of the non-Abelian statistics of both MZMs and Dirac fermion zero modes in different parameter regimes.In particular,we introduce a minimal tri-junction setting based on the minimal Kitaev chain model and show it facilitates the unified scheme of braiding Dirac fermion zero modes,as well as the MZMs in the assistance of a Dirac mode.This unified minimal model provides deeper insights into non-Abelian statistics,demonstrating that the non-Abelian braiding of MZMs can be continuously extended to encompass Dirac fermion zero modes.The minimal Kitaev chain has been realized in coupled quantum dots(Nature 614,445(2023);Nature 641,890(2025)).Our extension,which demonstrates novel nontrivial phases with non-Abelian MZM pairs and Dirac zero modes emerging in the broader parameter regimes without fine-tuning,expands the accessible experimental parameter space and enhances the feasibility of observing non-Abelian statistics in the minimal Kitaev chain model.展开更多
Quantum Hall effects have remained at the forefront of condensed matter physics research for decades,earning three Nobel Prizes in physics as a testament to their significance.In 1980,von Klitzing et al.discovered dis...Quantum Hall effects have remained at the forefront of condensed matter physics research for decades,earning three Nobel Prizes in physics as a testament to their significance.In 1980,von Klitzing et al.discovered discrete Hall conductance_(xy)=e^(2)/h g in a two-dimensional electron gas subjected to a magnetic field,where n represents the number of occupied Landau levels.This groundbreaking discovery is famously known as the integer quantum Hall effect and has been generalized in both fractional and anomalous ways(Fig.S1 online).展开更多
The discovery of the quantum Hall effect in the presence of a relatively strong magnetic field has profoundly inspired the study of topological phase of matter[1],[2],[3],which not only deepens our understanding of co...The discovery of the quantum Hall effect in the presence of a relatively strong magnetic field has profoundly inspired the study of topological phase of matter[1],[2],[3],which not only deepens our understanding of condensed materials beyond the scope of symmetry breaking but also holds significant promise in device application with low or even vanishing energy dissipation.In principle,since the role of magnetic field can be completely replaced by magnetic ordering,quantum Hall effect and its anomalous counterpart,termed quantum anomalous Hall effect(QAHE),typically appear as complementary pair.展开更多
As early as 1968,metallic hydrogen was considered a potential room-temperature superconductor within the frame of conventional theory for superconductivity[1].However,the metallization of elemental hydrogen needs extr...As early as 1968,metallic hydrogen was considered a potential room-temperature superconductor within the frame of conventional theory for superconductivity[1].However,the metallization of elemental hydrogen needs extremely high pressure as a prerequisite,which is also a holy grail in high-pressure physics.In 2004,Ashcroft[2]proposed that the introduction of other chemical elements can stabilize the sublattice of metallic hydrogen at lower pressures,which is referred to as“chemical precompression”.展开更多
The interplay between novel topological states and superconductivity has garnered substantial interest due to its potential for topological quantum computing.The Josephson effect serves as a useful probe for edge supe...The interplay between novel topological states and superconductivity has garnered substantial interest due to its potential for topological quantum computing.The Josephson effect serves as a useful probe for edge superconductivity in these hybrid topological materials.In Josephson junctions based on topological materials,supercurrents exhibit unique quantum interference patterns,including the conventional Fraunhofer oscillations,theΦ_(0)-periodic oscillation,and the 2Φ_(0)-periodic oscillation in response to the external magnetic field(Φ_(0)=h/2e is the flux quantum,h the Planck constant,and e the electron charge).These interference patterns stem from varied Andreev reflection mechanisms and the associated current density profiles.This review seeks to comprehensively examine the theoretical and experimental advancements in understanding the quantum interference patterns of edge supercurrents in Josephson junctions based on quantum spin Hall,quantum Hall,and quantum anomalous Hall systems.展开更多
Under certain symmetries,degenerate points in three-dimensional metals form one-dimensional nodal lines.These nodal lines sometimes exhibit intricate knotted structures and have been studied in various contexts.As one...Under certain symmetries,degenerate points in three-dimensional metals form one-dimensional nodal lines.These nodal lines sometimes exhibit intricate knotted structures and have been studied in various contexts.As one of the most common physical perturbations,disorder effects often trigger novel quantum phase transitions.For nodal-knot phases,whether disorder can drive knot transitions remains an open and intriguing question.Employing renormalization-group calculations,we demonstrate that nodal-knot transitions emerge in the presence of weak disorder.Specifically,both chemical-potential-type and magnetic-type disorders can induce knot transitions,resulting in the emergence of distinct knot topologies.The transition can be quantitatively characterized by changes in topological invariants such as the knot Wilson loop integrals.Our findings open up a new avenue for manipulating the topology of nodal-knot phases through disorder effects.展开更多
The nontrivial band topology of Chern insulator can enrich the content of its Hofstadter butterfly spectra,which is closely related to recent experiments in twisted bilayer graphene and cold atom systems.We investigat...The nontrivial band topology of Chern insulator can enrich the content of its Hofstadter butterfly spectra,which is closely related to recent experiments in twisted bilayer graphene and cold atom systems.We investigate the Hofstadter spectrum for various models of Chern insulators under a rational fluxφ_(0)/q,hereφ_(0)=h/e and q being an integer.We find the number of splitting subbands is|q-C|with C denoting the Chern number of parent band.Importantly,anomalous open-orbital subbands with Chern numbers q-1 and-q-1 emerge unexpectedly,which are beyond the parameter window(-q/2,q/2)of the Diophantine equation studied by Thouless-Kohmoto-Nightingale-den Nijs[Phys.Rev.Lett.49,405(1982)].The emergence of anomalous open orbits can be traced by analyzing the evolution of the Hofstadter spectrum,identifying as a new type of topological phase transition.These novel findings not only pinpoint the peculiar Hofstadter spectrum of Chern insulator,but also provide routes to study exotic characteristics beyond the Landau level physics.展开更多
Magnon,the quanta of spin wave,low energy excitation from magnetic ground state,not only carries spin angular momentum which is of crucial importance in new generation of information technology,but also serves as powe...Magnon,the quanta of spin wave,low energy excitation from magnetic ground state,not only carries spin angular momentum which is of crucial importance in new generation of information technology,but also serves as powerful probes for investigating the corresponding ground-state properties.Here,we investigate magnetic order transitions in the antiferromagnetic van der Waals insulator NiPS3 using non-local magnon transport.We observe a dimensional cross-over behavior with a critical thickness of approximately 12-14 nm.Below the threshold,the thermally activated magnon carries angular momentum that is opposite to the conventional case,corresponding to the vestigial order with higher symmetry.While above this critical thickness,where NiPS3 exhibits in-plane zigzag antiferromagnetic order with lower symmetry,the thermally activated magnon signals show anomalous high-magnetic-field responses.After the spin-flop transition,the Néel vector becomes strongly pinned near the a-axis,resulting in a flattening of the detected signals that can only be switched when the magnetic field is oriented perpendicular to the Néel vector.These findings demonstrate that magnon spin currents provide an effective means to investigate exotic orders and phase transitions in van der Waals magnetic insulators,offering new insights for both fundamental research and potential applications in spin-based technologies.展开更多
Based on the tight-binding calculations on honeycomb lattice and photonic experimental visualization on artificial graphene(AG), we report the domain-wall-induced gapped topological kink states and topological corner ...Based on the tight-binding calculations on honeycomb lattice and photonic experimental visualization on artificial graphene(AG), we report the domain-wall-induced gapped topological kink states and topological corner states. In honeycomb lattice, domain walls(DWs) with gapless topological kink states could be induced either by sublattice symmetry breaking or by lattice deformation. We find that the coexistence of these two mechanisms will induce DWs with gapped topological kink states. Significantly, the intersection of these two types of DWs gives rise to topological corner state localized at the crossing point.Through the manipulation of the DWs, we show AG with honeycomb lattice structure not only a versatile platform supporting multiple topological corner modes in a controlled manner, but also possessing promising applications such as fabricating topological quantum dots composed of gapped topological kink states and topological corner states.展开更多
Though several theoretical models have been proposed to design electronic flat-bands, the definite experimental realization in two-dimensional atomic crystal is still lacking. Here we propose a novel and realistic fla...Though several theoretical models have been proposed to design electronic flat-bands, the definite experimental realization in two-dimensional atomic crystal is still lacking. Here we propose a novel and realistic flat-band model based on threefold degenerate p-orbitals in two-dimensional ionic materials. Our theoretical analysis and first-principles calculations show that the proposed flat-band can be realized in 1 T layered materials of alkali-metal chalogenides and metal-carbon group compounds. Some of the former are theoretically predicted to be stable as layered materials(e.g., K2 S), and some of the latter have been experimentally fabricated in previous works(e.g., Gd2 CCl2). More interestingly, the flat-band is partially filled in the heterostructure of a K2 S monolayer and graphene layers. The spin polarized nearly flatband can be realized in the ferromagnetic state of a Gd2 CCl2 monolayer, which has been fabricated in experiments. Our theoretical model together with the material predictions provide a realistic platform for the study of flat-bands and related exotic quantum phases.展开更多
Pb nanobridges with a thickness of less than 10 nm and a width of several hundred nm have been fabricated from single-crystalline Pb fi lms using low-temperature molecular beam epitaxy and focus ion beam microfabricat...Pb nanobridges with a thickness of less than 10 nm and a width of several hundred nm have been fabricated from single-crystalline Pb fi lms using low-temperature molecular beam epitaxy and focus ion beam microfabrication techniques.We observed novel magnetoresistance oscillations below the superconducting transition temperature(TC)of the bridges.The oscillations which were not seen in the crystalline Pb fi lmsmay originate from the inhomogeneity of superconductivity induced by the applied magnetic fi elds on approaching the normal state,or the degradation of fi lm quality by thermal evolution.展开更多
Topological insulators,a class of typical topological materials in both two dimensions and three dimensions,are insulating in bulk and metallic at surface.The spin-momentum locked surface states and peculiar transport...Topological insulators,a class of typical topological materials in both two dimensions and three dimensions,are insulating in bulk and metallic at surface.The spin-momentum locked surface states and peculiar transport properties exhibit promising potential applications on quantum devices,which generate extensive interest in the last decade.Dephasing is the process of the loss of phase coherence,which inevitably exists in a realistic sample.In this review,we focus on recent progress in dephasing effects on the topological insulators.In general,there are two types of dephasing processes:normal dephasing and spin dephasing.In two-dimensional topological insulators,the phenomenologically numerical investigation shows that the longitudinal resistance plateaus is robust against normal dephasing but fragile with spin dephasing.Several microscopic mechanisms of spin dephasing are then discussed.In three-dimensional topological insulators,the helical surface states exhibit a helical spin texture due to the spin-momentum locking mechanism.Thus,normal dephasing has close connection to spin dephasing in this case,and gives rise to anomalous "gap-like" feature.Dephasing effects on properties of helical surface states are investigated.展开更多
In this work,we study the effects of disorder on topological metals that support a pair of helical edge modes deeply embedded inside the gapless bulk states.Strikingly,we predict that a quantum spin Hall(QSH)phase can...In this work,we study the effects of disorder on topological metals that support a pair of helical edge modes deeply embedded inside the gapless bulk states.Strikingly,we predict that a quantum spin Hall(QSH)phase can be obtained from such topological metals without opening a global band gap.To be specific,disorder can lead to a pair of robust helical edge states which is protected by an emergent Z2 topological invariant,giving rise to a quantized conductance plateau in transport measurements.These results are instructive for solving puzzles in various transport experiments on QSH materials that are intrinsically metallic.This work also will inspire experimental realization of the QSH effect in disordered topological metals.展开更多
The interplay between quenched disorder and critical behavior in quantum phase transitions is conceptually fascinating and of fundamental importance for understanding phase transitions. However, it is still unclear wh...The interplay between quenched disorder and critical behavior in quantum phase transitions is conceptually fascinating and of fundamental importance for understanding phase transitions. However, it is still unclear whether or not the quenched disorder influences the universality class of quantum phase transitions. More crucially, the absence of superconducting-metal transitions under in-plane magnetic fields in 2D superconductors imposes constraints on the universality of quantum criticality. Here, we observe the thickness-tuned universality class of superconductor-metal transition by changing the disorder strength in b - W films with varying thickness. The finite-size scaling uncovers the switch of universality class: quantum Griffiths singularity to multiple quantum criticality at a critical thickness of tc⊥1~ 8 nm and then from multiple quantum criticality to single criticality at tc⊥2~ 16 nm. Moreover, the superconducting-metal transition is observed for the first time under in-plane magnetic fields and the universality class is changed at tc‖~ 8 nm. The observation of thickness-tuned universality class under both out-of-plane and in-plane magnetic fields provides broad information for the disorder effect on superconducting-metal transitions and quantum criticality.展开更多
Scaling theory predicts complete localization in d = 2 in quantum systems belonging to the orthogonal class(i.e., with timereversal symmetry and spin-rotation symmetry). The conductance g behaves as g^exp(-L/l) with s...Scaling theory predicts complete localization in d = 2 in quantum systems belonging to the orthogonal class(i.e., with timereversal symmetry and spin-rotation symmetry). The conductance g behaves as g^exp(-L/l) with system size L and localization length l in the strong disorder limit. However, classical systems can always have metallic states in which Ohm’s law shows a constant g in d=2. We study a two-dimensional quantum percolation model by controlling dephasing effects. The numerical investigation of g aims at simulating a quantum-to-classical percolation evolution. An unexpected metallic phase, where g increases with L, generates immense interest before the system becomes completely classical. Furthermore, the analysis of the scaling plot of g indicates a metal-insulator crossover.展开更多
A quantized Hall conductance(not conductivity)in three dimensions has been searched for more than 30 years.Here we explore it in 3D topological nodal-ring semimetals,by employing a minimal model describing the essenti...A quantized Hall conductance(not conductivity)in three dimensions has been searched for more than 30 years.Here we explore it in 3D topological nodal-ring semimetals,by employing a minimal model describing the essential physics.In particular,the bulk topology can be captured by a momentum-dependent winding number,which confines the drumhead surface states in a specific momentum region.This confinement leads to a surface quantum Hall conductance in a specific energy window in this 3D system.The winding number for the drumhead surface states and Chern number for their quantum Hall effect form a two-fold topological hierarchy.We demonstrate the one-to-one correspondence between the momentum-dependent winding number and wavefunction of the drumhead surface states.More importantly,we stress that breaking chiral symmetry is necessary for the quantum Hall effect of the drumhead surface states.The analytic theory can be verified numerically by the Kubo formula for the Hall conductance.We propose an experimental setup to distinguish the surface and bulk quantum Hall effects.The theory will be useful for ongoing explorations on nodal-ring semimetals.展开更多
基金Supported by the National Key R&D Program of China(Grant Nos.2019YFA0308401 and 2017YFA0303301)the National Natural Science Foundation of China(Grant Nos.11974025,11674009,and 11934016)+1 种基金the Beijing Natural Science Foundation(Grant No.1192009)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB28000000)。
文摘We report the experimental investigation of the superconductor-metal quantum phase transition of the Eu O/KTa O3 interface.Around the transition,a divergence of the dynamical critical exponent is observed,which supports the quantum Griffiths singularity in the Eu O/KTa O3 interface.The quantum Griffiths singularity could be attributed to large rare superconducting regions and quenched disorders at the interface.Our results could pave the way for studying the exotic superconducting properties at the Eu O/KTa O3 interface.
基金supported by the National Key R&D Program of China (Grant Nos. 2024YFA1409000, and 2021YFA1400900)the Innovation Program for Quantum Science and Technology (Grant Nos. 2021ZD0302400, and 2021ZD0302000)+3 种基金the National Natural Science Foundation of China (Grant Nos. 12304194, 12574171, 12425401, and 12261160368)Shanghai Municipal Science and Technology (Grant No. 24DP2600100)Shanghai Pilot Program for Basic Research-Fudan University 1TQ1400100 (25TQ003)Shanghai Science and Technology Innovation Action Plan (Grant No. 24LZ1400800)
文摘Majorana zero modes(MZMs)are the most intensively studied non-Abelian anyons.The Dirac fermion zero modes in topological insulators,which are symmetry-protected doubling of MZMs under fermion number conservation,offer an alternative approach to explore non-Abelian anyons.However,a unified model that elucidates the braiding statistics of these types of topological zero modes remains absent.We show that the minimal Kitaev chain model beyond fine-tuning regime provides a unified characterization of the non-Abelian statistics of both MZMs and Dirac fermion zero modes in different parameter regimes.In particular,we introduce a minimal tri-junction setting based on the minimal Kitaev chain model and show it facilitates the unified scheme of braiding Dirac fermion zero modes,as well as the MZMs in the assistance of a Dirac mode.This unified minimal model provides deeper insights into non-Abelian statistics,demonstrating that the non-Abelian braiding of MZMs can be continuously extended to encompass Dirac fermion zero modes.The minimal Kitaev chain has been realized in coupled quantum dots(Nature 614,445(2023);Nature 641,890(2025)).Our extension,which demonstrates novel nontrivial phases with non-Abelian MZM pairs and Dirac zero modes emerging in the broader parameter regimes without fine-tuning,expands the accessible experimental parameter space and enhances the feasibility of observing non-Abelian statistics in the minimal Kitaev chain model.
基金supported by the National Key R&D Program of China(2022YFA1403700)Innovation Program for Quantum Science and Technology(2021ZD0302400)+4 种基金the National Natural Science Foundation of China(12525401,12304196,12350402,and 11925402)Guangdong Basic and Applied Basic Research Foundation(2022A1515111034 and 2023B0303000011),Guangdong Provincial(GDZX2201001and GDZX2401001)Guangdongprovince(2020KCXTD001)the Science,Technology and Innovation Commission of Shenzhen Municipality(ZDSYS20190902092905285)New Cornerstone Science Foundation through the XPLORER PRIZE,and Center for Computational Science and Engineering of SUSTech.
文摘Quantum Hall effects have remained at the forefront of condensed matter physics research for decades,earning three Nobel Prizes in physics as a testament to their significance.In 1980,von Klitzing et al.discovered discrete Hall conductance_(xy)=e^(2)/h g in a two-dimensional electron gas subjected to a magnetic field,where n represents the number of occupied Landau levels.This groundbreaking discovery is famously known as the integer quantum Hall effect and has been generalized in both fractional and anomalous ways(Fig.S1 online).
基金supported by the National Key R&D Program of China(2022YFA1403700 and 2024YFA1409003)the National Natural Science Foundation of China(12204044,12350401,and 12404056)the Shanghai Science and Technology Innovation Action Plan(24LZ1400800).
文摘The discovery of the quantum Hall effect in the presence of a relatively strong magnetic field has profoundly inspired the study of topological phase of matter[1],[2],[3],which not only deepens our understanding of condensed materials beyond the scope of symmetry breaking but also holds significant promise in device application with low or even vanishing energy dissipation.In principle,since the role of magnetic field can be completely replaced by magnetic ordering,quantum Hall effect and its anomalous counterpart,termed quantum anomalous Hall effect(QAHE),typically appear as complementary pair.
文摘As early as 1968,metallic hydrogen was considered a potential room-temperature superconductor within the frame of conventional theory for superconductivity[1].However,the metallization of elemental hydrogen needs extremely high pressure as a prerequisite,which is also a holy grail in high-pressure physics.In 2004,Ashcroft[2]proposed that the introduction of other chemical elements can stabilize the sublattice of metallic hydrogen at lower pressures,which is referred to as“chemical precompression”.
基金supported by the National Natural Science Foundation of China(Grant Nos.12204053,and 92265103)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302400)。
文摘The interplay between novel topological states and superconductivity has garnered substantial interest due to its potential for topological quantum computing.The Josephson effect serves as a useful probe for edge superconductivity in these hybrid topological materials.In Josephson junctions based on topological materials,supercurrents exhibit unique quantum interference patterns,including the conventional Fraunhofer oscillations,theΦ_(0)-periodic oscillation,and the 2Φ_(0)-periodic oscillation in response to the external magnetic field(Φ_(0)=h/2e is the flux quantum,h the Planck constant,and e the electron charge).These interference patterns stem from varied Andreev reflection mechanisms and the associated current density profiles.This review seeks to comprehensively examine the theoretical and experimental advancements in understanding the quantum interference patterns of edge supercurrents in Josephson junctions based on quantum spin Hall,quantum Hall,and quantum anomalous Hall systems.
基金supported by the National Key R&D Program of China(2022YFA1403700)the Innovation Program for Quantum Science and Technology(2021ZD0302400)+6 种基金the National Natural Science Foundation of China(12350402,12304074,12234017,and 12525401)the Guangdong Province(2020KCXTD001)the Guangdong Basic and Applied Basic Research Foundation(2023B0303000011)the Guangdong Provincial Quantum Science Strategic Initiative(GDZX2201001 and GDZX2401001)the Science,Technology and Innovation Commission of Shenzhen Municipality(ZDSYS20190902092905285)the New Corner-stone Science Foundation through the XPLORER PRIZE,and Center for Computational Science and Engineering of SUSTechsupported by the China National Postdoctoral Program for Innovative Talents(BX20240004).
文摘Under certain symmetries,degenerate points in three-dimensional metals form one-dimensional nodal lines.These nodal lines sometimes exhibit intricate knotted structures and have been studied in various contexts.As one of the most common physical perturbations,disorder effects often trigger novel quantum phase transitions.For nodal-knot phases,whether disorder can drive knot transitions remains an open and intriguing question.Employing renormalization-group calculations,we demonstrate that nodal-knot transitions emerge in the presence of weak disorder.Specifically,both chemical-potential-type and magnetic-type disorders can induce knot transitions,resulting in the emergence of distinct knot topologies.The transition can be quantitatively characterized by changes in topological invariants such as the knot Wilson loop integrals.Our findings open up a new avenue for manipulating the topology of nodal-knot phases through disorder effects.
基金supported by the National Basic Research Program of China(Grant No.2017YFA0303301)the National Natural Science Foundation of China(Grant Nos.12022407,and 11974256)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB28000000)。
文摘The nontrivial band topology of Chern insulator can enrich the content of its Hofstadter butterfly spectra,which is closely related to recent experiments in twisted bilayer graphene and cold atom systems.We investigate the Hofstadter spectrum for various models of Chern insulators under a rational fluxφ_(0)/q,hereφ_(0)=h/e and q being an integer.We find the number of splitting subbands is|q-C|with C denoting the Chern number of parent band.Importantly,anomalous open-orbital subbands with Chern numbers q-1 and-q-1 emerge unexpectedly,which are beyond the parameter window(-q/2,q/2)of the Diophantine equation studied by Thouless-Kohmoto-Nightingale-den Nijs[Phys.Rev.Lett.49,405(1982)].The emergence of anomalous open orbits can be traced by analyzing the evolution of the Hofstadter spectrum,identifying as a new type of topological phase transition.These novel findings not only pinpoint the peculiar Hofstadter spectrum of Chern insulator,but also provide routes to study exotic characteristics beyond the Landau level physics.
基金supported by the National Key R&D Program of China(Grant No.2024YFA1409001)the Innovation Program for Quantum Science and Technology(2021ZD0302403)+2 种基金the National Natural Science Foundation of China(Grant Nos.92265106,and 12404193)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000)the China Postdoctoral Science Foundation(Grant No.GZB20240029).
文摘Magnon,the quanta of spin wave,low energy excitation from magnetic ground state,not only carries spin angular momentum which is of crucial importance in new generation of information technology,but also serves as powerful probes for investigating the corresponding ground-state properties.Here,we investigate magnetic order transitions in the antiferromagnetic van der Waals insulator NiPS3 using non-local magnon transport.We observe a dimensional cross-over behavior with a critical thickness of approximately 12-14 nm.Below the threshold,the thermally activated magnon carries angular momentum that is opposite to the conventional case,corresponding to the vestigial order with higher symmetry.While above this critical thickness,where NiPS3 exhibits in-plane zigzag antiferromagnetic order with lower symmetry,the thermally activated magnon signals show anomalous high-magnetic-field responses.After the spin-flop transition,the Néel vector becomes strongly pinned near the a-axis,resulting in a flattening of the detected signals that can only be switched when the magnetic field is oriented perpendicular to the Néel vector.These findings demonstrate that magnon spin currents provide an effective means to investigate exotic orders and phase transitions in van der Waals magnetic insulators,offering new insights for both fundamental research and potential applications in spin-based technologies.
基金This work was supported by the National Basic Research Program of China(2019YFA0308403)the National Natural Science Foundation of China(11534001,11822407 and 11874274)+2 种基金Natural Science Foundation of Jiangsu Province(BK20170058)a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)We are grateful to H.M.Weng and H.W.Liu for helpful discussion.
文摘Based on the tight-binding calculations on honeycomb lattice and photonic experimental visualization on artificial graphene(AG), we report the domain-wall-induced gapped topological kink states and topological corner states. In honeycomb lattice, domain walls(DWs) with gapless topological kink states could be induced either by sublattice symmetry breaking or by lattice deformation. We find that the coexistence of these two mechanisms will induce DWs with gapped topological kink states. Significantly, the intersection of these two types of DWs gives rise to topological corner state localized at the crossing point.Through the manipulation of the DWs, we show AG with honeycomb lattice structure not only a versatile platform supporting multiple topological corner modes in a controlled manner, but also possessing promising applications such as fabricating topological quantum dots composed of gapped topological kink states and topological corner states.
基金supported by the National Basic Research Program of China(2015CB921102 and 2019YFA0308403)the National Natural Science Foundation of China(11674028 and11822407)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(XDB28000000)China Postdoctoral Science Foundation(2020M670011)。
文摘Though several theoretical models have been proposed to design electronic flat-bands, the definite experimental realization in two-dimensional atomic crystal is still lacking. Here we propose a novel and realistic flat-band model based on threefold degenerate p-orbitals in two-dimensional ionic materials. Our theoretical analysis and first-principles calculations show that the proposed flat-band can be realized in 1 T layered materials of alkali-metal chalogenides and metal-carbon group compounds. Some of the former are theoretically predicted to be stable as layered materials(e.g., K2 S), and some of the latter have been experimentally fabricated in previous works(e.g., Gd2 CCl2). More interestingly, the flat-band is partially filled in the heterostructure of a K2 S monolayer and graphene layers. The spin polarized nearly flatband can be realized in the ferromagnetic state of a Gd2 CCl2 monolayer, which has been fabricated in experiments. Our theoretical model together with the material predictions provide a realistic platform for the study of flat-bands and related exotic quantum phases.
基金by the National Science Foundation and the Ministry of Science and Technology of China and the Penn.State MRSEC under NSF grant DMR-0820404.
文摘Pb nanobridges with a thickness of less than 10 nm and a width of several hundred nm have been fabricated from single-crystalline Pb fi lms using low-temperature molecular beam epitaxy and focus ion beam microfabrication techniques.We observed novel magnetoresistance oscillations below the superconducting transition temperature(TC)of the bridges.The oscillations which were not seen in the crystalline Pb fi lmsmay originate from the inhomogeneity of superconductivity induced by the applied magnetic fi elds on approaching the normal state,or the degradation of fi lm quality by thermal evolution.
基金We are grateful to Y. Q. Li, Q. F. Sun and S. G. Cheng for collaboration and for their important contributions reviewed in this paper.supported by the National Natural Science Foundation of China (Grant Nos.11534001,11822407,and 11674028)NBRPC (Grant Nos. 2017YFA0303301 and 2017YFA0304600)NSF of Jiangsu Province,China (Grant No. BK20160007).H.Jiang was also funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘Topological insulators,a class of typical topological materials in both two dimensions and three dimensions,are insulating in bulk and metallic at surface.The spin-momentum locked surface states and peculiar transport properties exhibit promising potential applications on quantum devices,which generate extensive interest in the last decade.Dephasing is the process of the loss of phase coherence,which inevitably exists in a realistic sample.In this review,we focus on recent progress in dephasing effects on the topological insulators.In general,there are two types of dephasing processes:normal dephasing and spin dephasing.In two-dimensional topological insulators,the phenomenologically numerical investigation shows that the longitudinal resistance plateaus is robust against normal dephasing but fragile with spin dephasing.Several microscopic mechanisms of spin dephasing are then discussed.In three-dimensional topological insulators,the helical surface states exhibit a helical spin texture due to the spin-momentum locking mechanism.Thus,normal dephasing has close connection to spin dephasing in this case,and gives rise to anomalous "gap-like" feature.Dephasing effects on properties of helical surface states are investigated.
基金supported by the National Basic Research Program of China(Grant No.2015CB921102)the National Natural Science Foundation of China(Grant Nos.11534001,11822407,11704106,and 11974256)+3 种基金the Fundamental Research Funds for the Central Universitiesfunded by the Priority Academic Program Development of Jiangsu Higher Education InstitutionsNational Natural Science Foundation of China of Jiangsu province(Grant No.BK20190813)supported by the Chutian Scholars Program in Hubei Province。
文摘In this work,we study the effects of disorder on topological metals that support a pair of helical edge modes deeply embedded inside the gapless bulk states.Strikingly,we predict that a quantum spin Hall(QSH)phase can be obtained from such topological metals without opening a global band gap.To be specific,disorder can lead to a pair of robust helical edge states which is protected by an emergent Z2 topological invariant,giving rise to a quantized conductance plateau in transport measurements.These results are instructive for solving puzzles in various transport experiments on QSH materials that are intrinsically metallic.This work also will inspire experimental realization of the QSH effect in disordered topological metals.
基金supported by the National Key R&D Program of China(2019YFA0308402 and 2018YFA0305604)the Innovation Program for Quantum Science and Technology(2021ZD0302403)+1 种基金the National Natural Science Foundation of China(11934001,92265106,11774010,and 11921005)Beijing Municipal Natural Science Foundation(JQ20002)。
基金supported by the National Key Research and Development Program of China (2017YFA0303302, 2018YFA030560 and 2017YFA0303301)the National Natural Science Foundation of China (11934005, 11474058, 11874116, 11674028 and 11534001)+9 种基金the National Natural Science Foundation of China (U1932154)the Science and Technology Commission of Shanghai (19511120500)the Shanghai Municipal Science and Technology Major Project (2019SHZDZX01)the Program of Shanghai Academic/Technology Research Leader (20XD1400200)supported by National Science Foundation Cooperative Agreement No. DMR-1644779, No. DMR-1157490the State of Floridasupport from China Postdoctoral Innovative Talents Support Program (BX20190085)China Postdoctoral Science Foundation (2019 M661331)supported by the Scientific Instrument Developing Project of CAS (YJKYYQ20180059)the Youth Innovation Promotion Association CAS (2018486)。
文摘The interplay between quenched disorder and critical behavior in quantum phase transitions is conceptually fascinating and of fundamental importance for understanding phase transitions. However, it is still unclear whether or not the quenched disorder influences the universality class of quantum phase transitions. More crucially, the absence of superconducting-metal transitions under in-plane magnetic fields in 2D superconductors imposes constraints on the universality of quantum criticality. Here, we observe the thickness-tuned universality class of superconductor-metal transition by changing the disorder strength in b - W films with varying thickness. The finite-size scaling uncovers the switch of universality class: quantum Griffiths singularity to multiple quantum criticality at a critical thickness of tc⊥1~ 8 nm and then from multiple quantum criticality to single criticality at tc⊥2~ 16 nm. Moreover, the superconducting-metal transition is observed for the first time under in-plane magnetic fields and the universality class is changed at tc‖~ 8 nm. The observation of thickness-tuned universality class under both out-of-plane and in-plane magnetic fields provides broad information for the disorder effect on superconducting-metal transitions and quantum criticality.
基金supported by the National Basic Research Program of China(Grant Nos.2015CB921102,2017YFA0303301,and 2017YFA0304600)National Natural Science Foundation of China(Grant Nos.11504008,11574245,11674028,and 11822407)
文摘Scaling theory predicts complete localization in d = 2 in quantum systems belonging to the orthogonal class(i.e., with timereversal symmetry and spin-rotation symmetry). The conductance g behaves as g^exp(-L/l) with system size L and localization length l in the strong disorder limit. However, classical systems can always have metallic states in which Ohm’s law shows a constant g in d=2. We study a two-dimensional quantum percolation model by controlling dephasing effects. The numerical investigation of g aims at simulating a quantum-to-classical percolation evolution. An unexpected metallic phase, where g increases with L, generates immense interest before the system becomes completely classical. Furthermore, the analysis of the scaling plot of g indicates a metal-insulator crossover.
基金supported by the National Key R&D Program of China(2022YFA1403700)the Innovation Program for Quantum Science and Technology(2021ZD0302400)+3 种基金the National Natural Science Foundation of China(11925402,11534001,and 11974249)Guangdong province(2020KCXTD001 and 2016ZT06D348)the Natural Science Foundation of Shanghai(19ZR1437300)supported by Center for Computational Science and Engineering of SUSTech.
文摘A quantized Hall conductance(not conductivity)in three dimensions has been searched for more than 30 years.Here we explore it in 3D topological nodal-ring semimetals,by employing a minimal model describing the essential physics.In particular,the bulk topology can be captured by a momentum-dependent winding number,which confines the drumhead surface states in a specific momentum region.This confinement leads to a surface quantum Hall conductance in a specific energy window in this 3D system.The winding number for the drumhead surface states and Chern number for their quantum Hall effect form a two-fold topological hierarchy.We demonstrate the one-to-one correspondence between the momentum-dependent winding number and wavefunction of the drumhead surface states.More importantly,we stress that breaking chiral symmetry is necessary for the quantum Hall effect of the drumhead surface states.The analytic theory can be verified numerically by the Kubo formula for the Hall conductance.We propose an experimental setup to distinguish the surface and bulk quantum Hall effects.The theory will be useful for ongoing explorations on nodal-ring semimetals.
