We investigate the interplay between the pseudogap state and d-wave superconductivity in the two-dimensional doped Hubbard model by employing an eight-site cluster dynamical mean-field theory method.By tuning electron...We investigate the interplay between the pseudogap state and d-wave superconductivity in the two-dimensional doped Hubbard model by employing an eight-site cluster dynamical mean-field theory method.By tuning electron hopping parameters,the strong-coupling pseudogap in the two-dimensional Hubbard model can be either enhanced or suppressed in the doped Mott insulator regime.We find that in underdoped cases,the closing of pseudogap leads to a significant enhancement of superconductivity,indicating competition between the two in the underdoped regime.In contrast,at large dopings,suppressing the pseudogap is accompanied by a concurrent decrease in the superconducting transition temperature Tc,which can be attributed to a reduction in antiferromagnetic correlations behind both the pseudogap and superconductivity.We elucidate this evolving relationship between pseudogap and superconductivity across different doping regimes.展开更多
In moiré-patterned van der Waals structures of transition metal dichalcogenides,correlated insulators can form under integer and fractional fillings,whose transport properties are governed by various quasiparticl...In moiré-patterned van der Waals structures of transition metal dichalcogenides,correlated insulators can form under integer and fractional fillings,whose transport properties are governed by various quasiparticle excitations including holons,doublons and interlayer exciton insulators.Here we theoretically investigate the nearest-neighbor inter-site hoppings of holons and interlayer exciton insulators.Our analysis indicates that these hopping strengths are significantly enhanced compared to that of a single carrier.The underlying mechanism can be attributed to the strong Coulomb interaction between carriers at different sites.For the interlayer exciton insulator consisting of a holon and a carrier in different layers,we have also obtained its effective Bohr radius and energy splitting between the ground and the first-excited states.展开更多
Higher-order band topology not only enriches our understanding of topological phases but also unveils pioneering lower-dimensional boundary states,which harbors substantial potential for next-generation device applica...Higher-order band topology not only enriches our understanding of topological phases but also unveils pioneering lower-dimensional boundary states,which harbors substantial potential for next-generation device applications.The distinct electronic configurations and tunable attributes of two-dimensional materials position them as a quintessential platform for the realization of second-order topological insulators(SOTIs).This article provides an overview of the research progress in SOTIs within the field of two-dimensional electronic materials,focusing on the characterization of higher-order topological properties and the numerous candidate materials proposed in theoretical studies.These endeavors not only enhance our understanding of higher-order topological states but also highlight potential material systems that could be experimentally realized.展开更多
Atmospheric particle adsorption on insulator surfaces,coupled with humid environments,significantly affects contamination flashover,necessitating a clear understanding of the electric field distribution on insulator s...Atmospheric particle adsorption on insulator surfaces,coupled with humid environments,significantly affects contamination flashover,necessitating a clear understanding of the electric field distribution on insulator surfaces with adsorbed particles.This is crucial for accurately assessing insulator safety and informing critical decision-making.Although previous research has demonstrated that particle arrangement significantly influences the electric field distribution around transmission lines,an in-depth analysis of its effects on insulator surfaces remains lacking.To address this gap,this study establishes a composite insulator model to examine how three types of spherical contamination layers affect the electric field distribution on insulator surfaces under varying environmental conditions.The results reveal that in dry environments,the electric field strength at the apex of single-particle contamination layers increases with the particle size and relative permittivity.For the double-particle contamination layers,the electric field intensity on the insulator surface decreases as the particle spacing increases,and larger particles are more likely to attract smaller charged particles.For triple-particle contamination layers arranged in a triangular pattern,the maximum surface field strength is nearly double that of the chain-arranged particles.Furthermore,within the chain-arranged triple-particle contamination layers,a large-small-large size arrangement has a more pronounced impact on the surface electric field than a small-large-small size arrangement.In humid environments,the surface electric field strength of insulators decreases with increasing contamination levels.These findings are of significant theoretical and practical importance for ensuring the safe operation of power systems.展开更多
Recent studies have successfully demonstrated high-Tc superconductivity in bilayer nickelate La3Ni2O7.However,research on modulating the structural and transport characteristics of La3Ni2O7 films by applying“chemical...Recent studies have successfully demonstrated high-Tc superconductivity in bilayer nickelate La3Ni2O7.However,research on modulating the structural and transport characteristics of La3Ni2O7 films by applying“chemical”compressive pressure through cation substitution is still limited.Here,we address this issue in the La_(3−x)Nd_(x)Ni_(2)O_(7)(x=0,1.0,1.5,2.0,and 2.5)thin film samples.It was found that using Nd3+with a smaller radius instead of La3+can reduce the c-axis lattice constant and shift the metal-insulator transition(MIT)temperature TMIT.To probe the origin of the MIT at cryogenic temperatures,experimental measurements of magnetoresistance were conducted,and theoretical analysis was carried out using the Kondo model,Hikami-Larkin-Nagaoka equation,and other methods.The results indicate that as Nd doping rises,the contributions of the Kondo effect and two-dimensional weak localization(WL)first decrease and then increase.The total contribution of WL and the Kondo effect in the mid-doped La_(1.5)Nd_(1.5)Ni_(2)O_(7)sample was the smallest,which to some extent explains the changes in TMIT.The Kondo effect dominates in other La_(3−x)Nd_(x)Ni_(2)O_(7)(x=0,1.0,2.0,and 2.5)samples.This work demonstrates that cation doping has a significant impact on bilayer nickelates,providing experimental evidence for understanding the physical mechanism of the MIT in bilayer nickelates.展开更多
The cubic pyrochlore Tl_(2)Ru_(2)O_(7) undergoes concurrently a metal–insulator transition (MIT) and a first-order structural transition at T_(MIT)≈120 K,below which the system was found to form one-dimensional spin...The cubic pyrochlore Tl_(2)Ru_(2)O_(7) undergoes concurrently a metal–insulator transition (MIT) and a first-order structural transition at T_(MIT)≈120 K,below which the system was found to form one-dimensional spin-one Haldane chains associated with an orbital ordering of Ru-4d electrons.With an aim to tune and access distinct ground states with strong entanglements of multiple degrees of freedom,i.e.,spin,orbital,charge,and lattice,we utilize a high-pressure approach to regulate the MIT of this system.Our detailed resistivityρ(T) measurements on the polycrystalline Tl_(2)Ru_(2)O_(7) samples under various hydrostatic pressures indeed reveal an unusual evolution of the electronic ground states.At first,the MIT is suppressed monotonically from 120 K at ambient to about 70 K at 1.5 GPa and then vanishes suddenly at about 1.8 GPa without achieving a metallic ground state.Meanwhile,the system evolves into a semiconducting ground state with magnitude ofρ(T) in the entire temperature range enhanced gradually by further increasing pressure.Prior to the abrupt disappearance of MIT,a new electronic order manifested as a kink-like anomaly inρ(T) emerges at T_(0)>T_(MIT) at 1.2 GPa and it continues to increase with pressure,producing a tricritical-point-like behavior in the T–P phase diagram of Tl_(2)Ru_(2)O_(7).The presence of two successive transitions at T_(0 )and T_(MIT )in the pressure range 1.2–1.5 GPa indicates an inhomogeneous electronic state nearby the tricritical point.At P≥3 GPa,another broad anomaly emerges inρ(T) at T_(1)>T_(0),and T_(1)continuously increases with pressure,dividing the semiconductingρ(T) into distinct thermally activated regions.These rich phenomena in the pressurized Tl_(2)Ru_(2)O_(7) should originate from the complex interplay of strongly entangled multiple quantum degrees of freedom in the system near the localized-to-itinerant crossover regime.展开更多
Topological insulators represent a new phase of matter,characterized by conductive surfaces,while their bulk remains insulating.When the dimension of the system exceeds that of the topological state by at least two,th...Topological insulators represent a new phase of matter,characterized by conductive surfaces,while their bulk remains insulating.When the dimension of the system exceeds that of the topological state by at least two,the insulators are classified as higher-order topological insulators(HOTI).The appearance of higher-order topological states,such as corner states,can be explained by the filling anomaly,which leads to the fractional spectral charges in the unit cell.Previously reported fractional charges have been quite limited in number and size.In this work,based on the two-dimensional(2D)Su-Schrieffer-Heeger model lattice,we demonstrated a new class of HOTIs with adjustable fractional charges that can take any value ranging from 0 to 1,achieved by utilizing the Lorentz transformation.Furthermore,this transformation generates novel bound-state-in-continuum-like corner states,even when the lattice is in a topological trivial phase,offering a new approach to light beam localization.This work paves the way for fabricating HOTIs with diverse corner states that offer promising applicative potential.展开更多
The excitonic insulator(EI)is a more than 60-year-old theoretical proposal that is still elusive.It is a purely quantum phenomenon involving the spontaneous generation of excitons in quantum mechanics and the spontane...The excitonic insulator(EI)is a more than 60-year-old theoretical proposal that is still elusive.It is a purely quantum phenomenon involving the spontaneous generation of excitons in quantum mechanics and the spontaneous condensation of excitons in quantum statistics.At this point,the excitons represent the ground state rather than the conventional excited state.Thus,the scarcity of candidate materials is a key factor contributing to the lack of recognized EI to date.In this review,we begin with the birth of EI,presenting the current state of the field and the main challenges it faces.We then focus on recent advances in the discovery and design of EIs based on the first-principles Bethe-Salpeter scheme,in particular the dark-exciton rule guided screening of materials.It not only opens up new avenues for realizing excitonic instability in direct-gap and wide-gap semiconductors,but also leads to the discovery of novel quantum states of matter such as half-EIs and spin-triplet EIs.Finally,we will look ahead to possible research pathways leading to the first recognized EI,both theoretically and computationally.展开更多
In this investigation,we delve into the interplay between strong interactions and intricate topological configurations,leading to emergent quantum states such as magnetic topological insulators.The crux of our researc...In this investigation,we delve into the interplay between strong interactions and intricate topological configurations,leading to emergent quantum states such as magnetic topological insulators.The crux of our research centers on elucidating how lattice symmetry modulates antiferromagnetic quantum Hall phenomena.Utilizing the spinful Harper-Hofstadter model enriched with a next-nearest-neighbor(NNN)hopping term,we discern a half-filling bandgap,paving the way for the manifestation of a quantum Hall insulator characterized by a Chern number,C=2.Upon integrating a checkerboardpatterned staggered potential(△)and the Hubbard interaction(U),the system exhibits complex dynamical behaviors.Marginal NNN hopping culminates in a Ne′el antiferromagnetic Mott insulator.In contrast,intensified hopping results in stripe antiferromagnetic configurations.Moreover,in the regime of limited NNN hopping,a C=1 Ne′el antiferromagnetic quantum Hall insulator emerges.A salient observation pertains to the manifestation of a C=1 antiferromagnetic quantum Hall insulator when spin-flip mechanisms are not offset by space group symmetries.These findings chart a pathway for further explorations into antiferromagnetic Quantum Hall States.展开更多
We investigate the localization and topological properties of the Haldane model under the influence of random flux and Anderson disorder. Our localization analysis reveals that random flux induces a transition from in...We investigate the localization and topological properties of the Haldane model under the influence of random flux and Anderson disorder. Our localization analysis reveals that random flux induces a transition from insulating to metallic states, while Anderson localization only arises under the modulation of Anderson disorder. By employing real-space topological invariant methods, we demonstrates that the system undergoes topological phase transitions under different disorder manipulations, whereas random flux modulation uniquely induces topological Anderson insulator phases, with the potential to generate states with opposite Chern numbers. These findings highlight the distinct roles of disorder in shaping the interplay between topology and localization, providing insights into stabilizing topological states and designing robust topological quantum materials.展开更多
We theoretically study the effect of a uniform orbital magnetic field on spin waves in a triangular lattice tetrahedral antiferromagnetic insulator without spin–orbit coupling. Through symmetry analysis and microscop...We theoretically study the effect of a uniform orbital magnetic field on spin waves in a triangular lattice tetrahedral antiferromagnetic insulator without spin–orbit coupling. Through symmetry analysis and microscopic calculation, we show that the optical spin wave mode at the Brillouin zone center can acquire a small orbital magnetic moment, although it exhibits no magnetic moment from the Zeeman coupling. Our results are potentially applicable to intercalated van der Waals materials and twisted double-bilayer graphene.展开更多
Electron-hole interactions play a crucial role in determining the optoelectronic properties of materials,and in lowdimensional systems this is especially true due to the decrease of screening.In this review,we focus o...Electron-hole interactions play a crucial role in determining the optoelectronic properties of materials,and in lowdimensional systems this is especially true due to the decrease of screening.In this review,we focus on one unique quantum phase induced by the electron-hole interaction in two-dimensional systems,known as“exciton insulators”(EIs).Although this phase of matter has been studied for more than half a century,suitable platforms for its stable realization remain scarce.We provide an overview of the strategies to realize EIs in accessible materials and structures,along with a discussion on some unique properties of EIs stemming from the band structures of these materials.Additionally,signatures in experiments to distinguish EIs are discussed.展开更多
Density order is usually a consequence of the competition between long-range and short-range interactions.Here we report a density ordered superfluid emergent from a homogeneous Mott insulator due to the competition b...Density order is usually a consequence of the competition between long-range and short-range interactions.Here we report a density ordered superfluid emergent from a homogeneous Mott insulator due to the competition between frustrations and local interactions.This transition is found in a Bose–Hubbard model on a frustrated triangle lattice with an extra pairing term.Furthermore,we find a quantum phase transition between two different density ordered superfluids,which is beyond the Landau–Ginzburg(LG)paradigm.A U(1)symmetry is emergent at the critical point,while the symmetry in each density ordered superfluid is Z_(2)×Z_(3).We call the transition a‘shamrock transition’,due to its degenerate ground state in the parameter space being a shamrock-like curve rather than a circle in an LG-type transition.Effective low energy theories are established for the two transitions mentioned above and we find their resemblance and differences with clock models.展开更多
High-pressure ultrafast dynamics,as a new crossed research direction,are sensitive to subtle non-equilibrium state changes that might be unresolved by equilibrium states measurements,providing crucial information for ...High-pressure ultrafast dynamics,as a new crossed research direction,are sensitive to subtle non-equilibrium state changes that might be unresolved by equilibrium states measurements,providing crucial information for studying delicate phase transitions caused by complex interactions in Mott insulators.With time-resolved transient reflectivity measurements,we identified the new phases in the spin–orbit Mott insulator Sr_(3)Ir_(2)O_7 at 300 K that was previously unidentified using conventional approaches such as x-ray diffraction.Significant pressure-dependent variation of the amplitude and lifetime obtained by fitting the reflectivity?R/R reveal the changes of electronic structure caused by lattice distortions,and reflect the critical phenomena of phase transitions.Our findings demonstrate the importance of ultrafast nonequilibrium dynamics under extreme conditions for understanding the phase transition of Mott insulators.展开更多
We present an infrared spectroscopy study of the magnetic topological insulator MnBi_(4)Te_7 with antiferromagnetic(AFM) order below the Neel temperature TN= 13 K. Our investigation reveals that the low-frequency opti...We present an infrared spectroscopy study of the magnetic topological insulator MnBi_(4)Te_7 with antiferromagnetic(AFM) order below the Neel temperature TN= 13 K. Our investigation reveals that the low-frequency optical conductivity consists of two Drude peaks, indicating a response of free carriers involving multiple bands. Interestingly, the narrow Drude peak grows strongly as the temperature decreases, while the broad Drude peak remains relatively unchanged. The onset of interband transitions starts around 2000 cm^(-1), followed by two prominent absorption peaks around 10000 cm^(-1) and 20000 cm^(-1). Upon cooling, there is a notable transfer of spectral weight from the interband transitions to the Drude response. Below TN, the AFM transition gives rise to small anomalies of the charge response due to a band reconstruction.These findings provide valuable insights into the interplay between magnetism and the electronic properties in MnBi_(4)Te_7.展开更多
Mottness is at the heart of the essential physics in a strongly correlated system as many novel quantum phenomena occur in the metallic phase near the Mott metal–insulator transition. We investigate the Mott transiti...Mottness is at the heart of the essential physics in a strongly correlated system as many novel quantum phenomena occur in the metallic phase near the Mott metal–insulator transition. We investigate the Mott transition in a Hubbard model by using the dynamical mean-field theory and introduce the local quantum state fidelity to depict the Mott metal–insulator transition. The local quantum state fidelity provides a convenient approach to determining the critical point of the Mott transition. Additionally, it presents a consistent description of the two distinct forms of the Mott transition points.展开更多
Recently,Chern insulators in an antiferromagnetic(AFM)phase have been suggested theoretically and predicted in a few materials.However,the experimental observation of two-dimensional(2D)AFM quantum anomalous Hall effe...Recently,Chern insulators in an antiferromagnetic(AFM)phase have been suggested theoretically and predicted in a few materials.However,the experimental observation of two-dimensional(2D)AFM quantum anomalous Hall effect is still a challenge to date.In this work,we propose that an AFM Chern insulator can be realized in a 2D monolayer of NiOsCl_(6)modulated by a compressive strain.Strain modulation is accessible experimentally and used widely in predicting and tuning topological nontrivial phases.With first-principles calculations,we have investigated the structural,magnetic,and electronic properties of NiOsCl_(6).Its stability has been confirmed through molecular dynamical simulations,elasticity constant,and phonon spectrum.It has a collinear AFM order,with opposite magnetic moments of 1.3μBon each Ni/Os atom,respectively,and the Neel temperature is estimated to be 93 K.In the absence of strain,it functions as an AFM insulator with a direct gap with spin-orbital coupling included.Compressive strain will induce a transition from a normal insulator to a Chern insulator characterized by a Chern number C=1,with a band gap of about 30 meV.This transition is accompanied by a structural distortion.Remarkably,the Chern insulator phase persists within the 3%-10%compressive strain range,offering an alternative platform for the utilization of AFM materials in spintronic devices.展开更多
Data augmentation is an important task of using existing data to expand data sets.Using generative countermeasure network technology to realize data augmentation has the advantages of high-quality generated samples,si...Data augmentation is an important task of using existing data to expand data sets.Using generative countermeasure network technology to realize data augmentation has the advantages of high-quality generated samples,simple training,and fewer restrictions on the number of generated samples.However,in the field of transmission line insulator images,the freely synthesized samples are prone to produce fuzzy backgrounds and disordered samples of the main insulator features.To solve the above problems,this paper uses the cycle generative adversarial network(Cycle-GAN)used for domain conversion in the generation countermeasure network as the initial framework and uses the self-attention mechanism and channel attention mechanism to assist the conversion to realize the mutual conversion of different insulator samples.The attention module with prior knowledge is used to build the generation countermeasure network,and the generative adversarial network(GAN)model with local controllable generation is built to realize the directional generation of insulator belt defect samples.The experimental results show that the samples obtained by this method are improved in a number of quality indicators,and the quality effect of the samples obtained is excellent,which has a reference value for the data expansion of insulator images.展开更多
Insulator defect detection plays a vital role in maintaining the secure operation of power systems.To address the issues of the difficulty of detecting small objects and missing objects due to the small scale,variable...Insulator defect detection plays a vital role in maintaining the secure operation of power systems.To address the issues of the difficulty of detecting small objects and missing objects due to the small scale,variable scale,and fuzzy edge morphology of insulator defects,we construct an insulator dataset with 1600 samples containing flashovers and breakages.Then a simple and effective surface defect detection method of power line insulators for difficult small objects is proposed.Firstly,a high-resolution featuremap is introduced and a small object prediction layer is added so that the model can detect tiny objects.Secondly,a simplified adaptive spatial feature fusion(SASFF)module is introduced to perform cross-scale spatial fusion to improve adaptability to variable multi-scale features.Finally,we propose an enhanced deformable attention mechanism(EDAM)module.By integrating a gating activation function,the model is further inspired to learn a small number of critical sampling points near reference points.And the module can improve the perception of object morphology.The experimental results indicate that concerning the dataset of flashover and breakage defects,this method improves the performance of YOLOv5,YOLOv7,and YOLOv8.In practical application,it can simply and effectively improve the precision of power line insulator defect detection and reduce missing detection for difficult small objects.展开更多
Disorder effects on topological materials in integer dimensions have been extensively explored in recent years. However, its influence on topological systems in fractional dimensions remains unclear. Here, we investig...Disorder effects on topological materials in integer dimensions have been extensively explored in recent years. However, its influence on topological systems in fractional dimensions remains unclear. Here, we investigate the disorder effects on a fractal system constructed on the Sierpiński lattice in fractional dimensions. The system supports the second-order topological insulator phase characterized by a quantized quadrupole moment and the normal insulator phase. We find that the second-order topological insulator phase on the Sierpiński lattice is robust against weak disorder but suppressed by strong disorder. Most interestingly, we find that disorder can transform the normal insulator phase to the second-order topological insulator phase with an emergent quantized quadrupole moment. Finally, the disorder-induced phase is further confirmed by calculating the energy spectrum and the corresponding probability distributions.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12274472,12494594,12494591,and 92165204)National Key Research and Development Program of China(Grant No.2022YFA1402802)+2 种基金Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices(Grant No.2022B1212010008)Guangdong Fundamental Research Center for Magnetoelectric Physics(Grant No.2024B0303390001)Guangdong Provincial Quantum Science Strategic Initiative(Grant No.GDZX2401010)。
文摘We investigate the interplay between the pseudogap state and d-wave superconductivity in the two-dimensional doped Hubbard model by employing an eight-site cluster dynamical mean-field theory method.By tuning electron hopping parameters,the strong-coupling pseudogap in the two-dimensional Hubbard model can be either enhanced or suppressed in the doped Mott insulator regime.We find that in underdoped cases,the closing of pseudogap leads to a significant enhancement of superconductivity,indicating competition between the two in the underdoped regime.In contrast,at large dopings,suppressing the pseudogap is accompanied by a concurrent decrease in the superconducting transition temperature Tc,which can be attributed to a reduction in antiferromagnetic correlations behind both the pseudogap and superconductivity.We elucidate this evolving relationship between pseudogap and superconductivity across different doping regimes.
基金support by the National Natural Sci-ence Foundation of China(Grant No.12274477)the De-partment of Science and Technology of Guangdong Provincein China(Grant No.2019QN01X061)。
文摘In moiré-patterned van der Waals structures of transition metal dichalcogenides,correlated insulators can form under integer and fractional fillings,whose transport properties are governed by various quasiparticle excitations including holons,doublons and interlayer exciton insulators.Here we theoretically investigate the nearest-neighbor inter-site hoppings of holons and interlayer exciton insulators.Our analysis indicates that these hopping strengths are significantly enhanced compared to that of a single carrier.The underlying mechanism can be attributed to the strong Coulomb interaction between carriers at different sites.For the interlayer exciton insulator consisting of a holon and a carrier in different layers,we have also obtained its effective Bohr radius and energy splitting between the ground and the first-excited states.
基金supported by the National Natu-ral Science Foundation of China(Grants No.12174220 and No.12074217)the Shandong Provincial Science Foundation for Excellent Young Scholars(Grant No.ZR2023YQ001)+1 种基金the Taishan Young Scholar Program of Shandong Provincethe Qilu Young Scholar Pro-gram of Shandong University.
文摘Higher-order band topology not only enriches our understanding of topological phases but also unveils pioneering lower-dimensional boundary states,which harbors substantial potential for next-generation device applications.The distinct electronic configurations and tunable attributes of two-dimensional materials position them as a quintessential platform for the realization of second-order topological insulators(SOTIs).This article provides an overview of the research progress in SOTIs within the field of two-dimensional electronic materials,focusing on the characterization of higher-order topological properties and the numerous candidate materials proposed in theoretical studies.These endeavors not only enhance our understanding of higher-order topological states but also highlight potential material systems that could be experimentally realized.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12064034 and 11562017)the Leading Talents Program of Science and Technology Innovation in Ningxia Hui Autonomous Region,China(Grant No.2020GKLRLX08)the Natural Science Foundation of Ningxia Hui Autonomous Region,China(Grant No.2024AAC05040)。
文摘Atmospheric particle adsorption on insulator surfaces,coupled with humid environments,significantly affects contamination flashover,necessitating a clear understanding of the electric field distribution on insulator surfaces with adsorbed particles.This is crucial for accurately assessing insulator safety and informing critical decision-making.Although previous research has demonstrated that particle arrangement significantly influences the electric field distribution around transmission lines,an in-depth analysis of its effects on insulator surfaces remains lacking.To address this gap,this study establishes a composite insulator model to examine how three types of spherical contamination layers affect the electric field distribution on insulator surfaces under varying environmental conditions.The results reveal that in dry environments,the electric field strength at the apex of single-particle contamination layers increases with the particle size and relative permittivity.For the double-particle contamination layers,the electric field intensity on the insulator surface decreases as the particle spacing increases,and larger particles are more likely to attract smaller charged particles.For triple-particle contamination layers arranged in a triangular pattern,the maximum surface field strength is nearly double that of the chain-arranged particles.Furthermore,within the chain-arranged triple-particle contamination layers,a large-small-large size arrangement has a more pronounced impact on the surface electric field than a small-large-small size arrangement.In humid environments,the surface electric field strength of insulators decreases with increasing contamination levels.These findings are of significant theoretical and practical importance for ensuring the safe operation of power systems.
基金supported by the Natural Science Foundation of Guangdong Province of China(Grant No.2025A1515011071)the National Natural Science Foundation of China(Grant Nos.92065110,11974048,and 12074334)the Beijing Municipal Natural Science Foundation Key Research Topics(Grant No.Z230006)。
文摘Recent studies have successfully demonstrated high-Tc superconductivity in bilayer nickelate La3Ni2O7.However,research on modulating the structural and transport characteristics of La3Ni2O7 films by applying“chemical”compressive pressure through cation substitution is still limited.Here,we address this issue in the La_(3−x)Nd_(x)Ni_(2)O_(7)(x=0,1.0,1.5,2.0,and 2.5)thin film samples.It was found that using Nd3+with a smaller radius instead of La3+can reduce the c-axis lattice constant and shift the metal-insulator transition(MIT)temperature TMIT.To probe the origin of the MIT at cryogenic temperatures,experimental measurements of magnetoresistance were conducted,and theoretical analysis was carried out using the Kondo model,Hikami-Larkin-Nagaoka equation,and other methods.The results indicate that as Nd doping rises,the contributions of the Kondo effect and two-dimensional weak localization(WL)first decrease and then increase.The total contribution of WL and the Kondo effect in the mid-doped La_(1.5)Nd_(1.5)Ni_(2)O_(7)sample was the smallest,which to some extent explains the changes in TMIT.The Kondo effect dominates in other La_(3−x)Nd_(x)Ni_(2)O_(7)(x=0,1.0,2.0,and 2.5)samples.This work demonstrates that cation doping has a significant impact on bilayer nickelates,providing experimental evidence for understanding the physical mechanism of the MIT in bilayer nickelates.
基金supported by the National Key Research and Development Program of China (Grant Nos. 2023YFA1406100 and 2021YFA1400200)the National Natural Science Foundation of China (Grant Nos. 12025408 and 12174424)+2 种基金the Youth Innovation Promotion Association of Chinese Academy of Scineces (Grant No. 2023007)support from the National Natural Science Foundation of China (Grant No. 11904272)the Open Fund of Hubei Provincial Key Laboratory of Metallurgical Industry Process Systems Science (Grant No. Z202202)。
文摘The cubic pyrochlore Tl_(2)Ru_(2)O_(7) undergoes concurrently a metal–insulator transition (MIT) and a first-order structural transition at T_(MIT)≈120 K,below which the system was found to form one-dimensional spin-one Haldane chains associated with an orbital ordering of Ru-4d electrons.With an aim to tune and access distinct ground states with strong entanglements of multiple degrees of freedom,i.e.,spin,orbital,charge,and lattice,we utilize a high-pressure approach to regulate the MIT of this system.Our detailed resistivityρ(T) measurements on the polycrystalline Tl_(2)Ru_(2)O_(7) samples under various hydrostatic pressures indeed reveal an unusual evolution of the electronic ground states.At first,the MIT is suppressed monotonically from 120 K at ambient to about 70 K at 1.5 GPa and then vanishes suddenly at about 1.8 GPa without achieving a metallic ground state.Meanwhile,the system evolves into a semiconducting ground state with magnitude ofρ(T) in the entire temperature range enhanced gradually by further increasing pressure.Prior to the abrupt disappearance of MIT,a new electronic order manifested as a kink-like anomaly inρ(T) emerges at T_(0)>T_(MIT) at 1.2 GPa and it continues to increase with pressure,producing a tricritical-point-like behavior in the T–P phase diagram of Tl_(2)Ru_(2)O_(7).The presence of two successive transitions at T_(0 )and T_(MIT )in the pressure range 1.2–1.5 GPa indicates an inhomogeneous electronic state nearby the tricritical point.At P≥3 GPa,another broad anomaly emerges inρ(T) at T_(1)>T_(0),and T_(1)continuously increases with pressure,dividing the semiconductingρ(T) into distinct thermally activated regions.These rich phenomena in the pressurized Tl_(2)Ru_(2)O_(7) should originate from the complex interplay of strongly entangled multiple quantum degrees of freedom in the system near the localized-to-itinerant crossover regime.
基金supported by the Natural Science Basic Research Program of Shaanxi Province(No.2024JC-JCQN-06)the National Natural Science Foundation of China(Nos.12474337,12304370)Fundamental Research Funds for the Central Universities(No.xzy012024135).
文摘Topological insulators represent a new phase of matter,characterized by conductive surfaces,while their bulk remains insulating.When the dimension of the system exceeds that of the topological state by at least two,the insulators are classified as higher-order topological insulators(HOTI).The appearance of higher-order topological states,such as corner states,can be explained by the filling anomaly,which leads to the fractional spectral charges in the unit cell.Previously reported fractional charges have been quite limited in number and size.In this work,based on the two-dimensional(2D)Su-Schrieffer-Heeger model lattice,we demonstrated a new class of HOTIs with adjustable fractional charges that can take any value ranging from 0 to 1,achieved by utilizing the Lorentz transformation.Furthermore,this transformation generates novel bound-state-in-continuum-like corner states,even when the lattice is in a topological trivial phase,offering a new approach to light beam localization.This work paves the way for fabricating HOTIs with diverse corner states that offer promising applicative potential.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2023YFA1406400 and 2020YFA0308800)the National Natural Science Foundation of China(Grant No.12474064)。
文摘The excitonic insulator(EI)is a more than 60-year-old theoretical proposal that is still elusive.It is a purely quantum phenomenon involving the spontaneous generation of excitons in quantum mechanics and the spontaneous condensation of excitons in quantum statistics.At this point,the excitons represent the ground state rather than the conventional excited state.Thus,the scarcity of candidate materials is a key factor contributing to the lack of recognized EI to date.In this review,we begin with the birth of EI,presenting the current state of the field and the main challenges it faces.We then focus on recent advances in the discovery and design of EIs based on the first-principles Bethe-Salpeter scheme,in particular the dark-exciton rule guided screening of materials.It not only opens up new avenues for realizing excitonic instability in direct-gap and wide-gap semiconductors,but also leads to the discovery of novel quantum states of matter such as half-EIs and spin-triplet EIs.Finally,we will look ahead to possible research pathways leading to the first recognized EI,both theoretically and computationally.
文摘In this investigation,we delve into the interplay between strong interactions and intricate topological configurations,leading to emergent quantum states such as magnetic topological insulators.The crux of our research centers on elucidating how lattice symmetry modulates antiferromagnetic quantum Hall phenomena.Utilizing the spinful Harper-Hofstadter model enriched with a next-nearest-neighbor(NNN)hopping term,we discern a half-filling bandgap,paving the way for the manifestation of a quantum Hall insulator characterized by a Chern number,C=2.Upon integrating a checkerboardpatterned staggered potential(△)and the Hubbard interaction(U),the system exhibits complex dynamical behaviors.Marginal NNN hopping culminates in a Ne′el antiferromagnetic Mott insulator.In contrast,intensified hopping results in stripe antiferromagnetic configurations.Moreover,in the regime of limited NNN hopping,a C=1 Ne′el antiferromagnetic quantum Hall insulator emerges.A salient observation pertains to the manifestation of a C=1 antiferromagnetic quantum Hall insulator when spin-flip mechanisms are not offset by space group symmetries.These findings chart a pathway for further explorations into antiferromagnetic Quantum Hall States.
基金Project supported by the National Key Research and Development Program of China (Grant Nos. 2021YFA1400900, 2021YFA0718300, and 2021YFA1402100)the National Natural Science Foundation of China (Grant Nos. 12174461, 12234012, 12334012, and 52327808)。
文摘We investigate the localization and topological properties of the Haldane model under the influence of random flux and Anderson disorder. Our localization analysis reveals that random flux induces a transition from insulating to metallic states, while Anderson localization only arises under the modulation of Anderson disorder. By employing real-space topological invariant methods, we demonstrates that the system undergoes topological phase transitions under different disorder manipulations, whereas random flux modulation uniquely induces topological Anderson insulator phases, with the potential to generate states with opposite Chern numbers. These findings highlight the distinct roles of disorder in shaping the interplay between topology and localization, providing insights into stabilizing topological states and designing robust topological quantum materials.
基金Project supported by the National Key R&D Program of China (Grant No. 2022YFA1403800)the National Natural Science Foundation of China (Grant Nos. 12250008 and 12188101)+1 种基金the Project for Young Scientists in Basic Research (Grant No. YSBR-059)performed in part at the Aspen Center for Physics, supported by the National Natural Science Foundation of China (Grant No. PHY2210452)。
文摘We theoretically study the effect of a uniform orbital magnetic field on spin waves in a triangular lattice tetrahedral antiferromagnetic insulator without spin–orbit coupling. Through symmetry analysis and microscopic calculation, we show that the optical spin wave mode at the Brillouin zone center can acquire a small orbital magnetic moment, although it exhibits no magnetic moment from the Zeeman coupling. Our results are potentially applicable to intercalated van der Waals materials and twisted double-bilayer graphene.
基金supported by the National Key Research&Development Program of China(Grant Nos.2022YFA1403500 and 2021YFA1400500)the National Science Foundation of China(Grant Nos.62321004,12234001,and 12474215)+1 种基金supported by New Cornerstone Science Foundationa fellowship and a CRF award from the Research Grants Council of the Hong Kong Special Administrative Region,China(Grant Nos.HKUST SRFS2324-6S01 and C7037-22GF)。
文摘Electron-hole interactions play a crucial role in determining the optoelectronic properties of materials,and in lowdimensional systems this is especially true due to the decrease of screening.In this review,we focus on one unique quantum phase induced by the electron-hole interaction in two-dimensional systems,known as“exciton insulators”(EIs).Although this phase of matter has been studied for more than half a century,suitable platforms for its stable realization remain scarce.We provide an overview of the strategies to realize EIs in accessible materials and structures,along with a discussion on some unique properties of EIs stemming from the band structures of these materials.Additionally,signatures in experiments to distinguish EIs are discussed.
基金supported by the Beijing Natural Science Foundation(Z180013)(YC)National Natural Science Foundation of China(NSFC)under Grant No.12174358(YC)and No.11734010(YC and CW)MOST Grant No.2016YFA0301600(CW)。
文摘Density order is usually a consequence of the competition between long-range and short-range interactions.Here we report a density ordered superfluid emergent from a homogeneous Mott insulator due to the competition between frustrations and local interactions.This transition is found in a Bose–Hubbard model on a frustrated triangle lattice with an extra pairing term.Furthermore,we find a quantum phase transition between two different density ordered superfluids,which is beyond the Landau–Ginzburg(LG)paradigm.A U(1)symmetry is emergent at the critical point,while the symmetry in each density ordered superfluid is Z_(2)×Z_(3).We call the transition a‘shamrock transition’,due to its degenerate ground state in the parameter space being a shamrock-like curve rather than a circle in an LG-type transition.Effective low energy theories are established for the two transitions mentioned above and we find their resemblance and differences with clock models.
基金The project supported by the National Key Research and Development Program of China(Grant No.2018YFA0305703)Science Challenge Project(Grant No.TZ2016001)the National Natural Science Foundation of China(Grant Nos.U1930401 and 11874075)。
文摘High-pressure ultrafast dynamics,as a new crossed research direction,are sensitive to subtle non-equilibrium state changes that might be unresolved by equilibrium states measurements,providing crucial information for studying delicate phase transitions caused by complex interactions in Mott insulators.With time-resolved transient reflectivity measurements,we identified the new phases in the spin–orbit Mott insulator Sr_(3)Ir_(2)O_7 at 300 K that was previously unidentified using conventional approaches such as x-ray diffraction.Significant pressure-dependent variation of the amplitude and lifetime obtained by fitting the reflectivity?R/R reveal the changes of electronic structure caused by lattice distortions,and reflect the critical phenomena of phase transitions.Our findings demonstrate the importance of ultrafast nonequilibrium dynamics under extreme conditions for understanding the phase transition of Mott insulators.
基金Project supported by the the National Natural Science Foundation of China (Grant No.12274442)the National Key R&D Program of China (Grant No.2022YFA1403901)。
文摘We present an infrared spectroscopy study of the magnetic topological insulator MnBi_(4)Te_7 with antiferromagnetic(AFM) order below the Neel temperature TN= 13 K. Our investigation reveals that the low-frequency optical conductivity consists of two Drude peaks, indicating a response of free carriers involving multiple bands. Interestingly, the narrow Drude peak grows strongly as the temperature decreases, while the broad Drude peak remains relatively unchanged. The onset of interband transitions starts around 2000 cm^(-1), followed by two prominent absorption peaks around 10000 cm^(-1) and 20000 cm^(-1). Upon cooling, there is a notable transfer of spectral weight from the interband transitions to the Drude response. Below TN, the AFM transition gives rise to small anomalies of the charge response due to a band reconstruction.These findings provide valuable insights into the interplay between magnetism and the electronic properties in MnBi_(4)Te_7.
基金Project supported by the Scientific Research Foundation for Youth Academic Talent of Inner Mongolia University (Grant No.1000023112101/010)the Fundamental Research Funds for the Central Universities of China (Grant No.JN200208)+2 种基金supported by the National Natural Science Foundation of China (Grant No.11474023)supported by the National Key Research and Development Program of China (Grant No.2021YFA1401803)the National Natural Science Foundation of China (Grant Nos.11974051 and 11734002)。
文摘Mottness is at the heart of the essential physics in a strongly correlated system as many novel quantum phenomena occur in the metallic phase near the Mott metal–insulator transition. We investigate the Mott transition in a Hubbard model by using the dynamical mean-field theory and introduce the local quantum state fidelity to depict the Mott metal–insulator transition. The local quantum state fidelity provides a convenient approach to determining the critical point of the Mott transition. Additionally, it presents a consistent description of the two distinct forms of the Mott transition points.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12104183,52173283,and 62071200)the Natural Science Foundation of Shandong Province,China(Grant Nos.ZR2021MA040 and ZR2023MA091)+2 种基金the Taishan Scholar Program of Shandong Province,China(Grant No.ts20190939)the Independent Cultivation Program of Innovation Team of Jinan City(Grant No.2021GXRC043)supported by high-performance computing platform at University of Jinan。
文摘Recently,Chern insulators in an antiferromagnetic(AFM)phase have been suggested theoretically and predicted in a few materials.However,the experimental observation of two-dimensional(2D)AFM quantum anomalous Hall effect is still a challenge to date.In this work,we propose that an AFM Chern insulator can be realized in a 2D monolayer of NiOsCl_(6)modulated by a compressive strain.Strain modulation is accessible experimentally and used widely in predicting and tuning topological nontrivial phases.With first-principles calculations,we have investigated the structural,magnetic,and electronic properties of NiOsCl_(6).Its stability has been confirmed through molecular dynamical simulations,elasticity constant,and phonon spectrum.It has a collinear AFM order,with opposite magnetic moments of 1.3μBon each Ni/Os atom,respectively,and the Neel temperature is estimated to be 93 K.In the absence of strain,it functions as an AFM insulator with a direct gap with spin-orbital coupling included.Compressive strain will induce a transition from a normal insulator to a Chern insulator characterized by a Chern number C=1,with a band gap of about 30 meV.This transition is accompanied by a structural distortion.Remarkably,the Chern insulator phase persists within the 3%-10%compressive strain range,offering an alternative platform for the utilization of AFM materials in spintronic devices.
基金supported in part by the National Natural Science Foundation of China under Grant No.61973055Fundamental Research Funds for the Central Universities under Grant No.ZYGX2020J011Regional Innovation Cooperation Funds of Sichuan under Grant No.2024YFHZ0089.
文摘Data augmentation is an important task of using existing data to expand data sets.Using generative countermeasure network technology to realize data augmentation has the advantages of high-quality generated samples,simple training,and fewer restrictions on the number of generated samples.However,in the field of transmission line insulator images,the freely synthesized samples are prone to produce fuzzy backgrounds and disordered samples of the main insulator features.To solve the above problems,this paper uses the cycle generative adversarial network(Cycle-GAN)used for domain conversion in the generation countermeasure network as the initial framework and uses the self-attention mechanism and channel attention mechanism to assist the conversion to realize the mutual conversion of different insulator samples.The attention module with prior knowledge is used to build the generation countermeasure network,and the generative adversarial network(GAN)model with local controllable generation is built to realize the directional generation of insulator belt defect samples.The experimental results show that the samples obtained by this method are improved in a number of quality indicators,and the quality effect of the samples obtained is excellent,which has a reference value for the data expansion of insulator images.
基金State Grid Jiangsu Electric Power Co.,Ltd.of the Science and Technology Project(Grant No.J2022004).
文摘Insulator defect detection plays a vital role in maintaining the secure operation of power systems.To address the issues of the difficulty of detecting small objects and missing objects due to the small scale,variable scale,and fuzzy edge morphology of insulator defects,we construct an insulator dataset with 1600 samples containing flashovers and breakages.Then a simple and effective surface defect detection method of power line insulators for difficult small objects is proposed.Firstly,a high-resolution featuremap is introduced and a small object prediction layer is added so that the model can detect tiny objects.Secondly,a simplified adaptive spatial feature fusion(SASFF)module is introduced to perform cross-scale spatial fusion to improve adaptability to variable multi-scale features.Finally,we propose an enhanced deformable attention mechanism(EDAM)module.By integrating a gating activation function,the model is further inspired to learn a small number of critical sampling points near reference points.And the module can improve the perception of object morphology.The experimental results indicate that concerning the dataset of flashover and breakage defects,this method improves the performance of YOLOv5,YOLOv7,and YOLOv8.In practical application,it can simply and effectively improve the precision of power line insulator defect detection and reduce missing detection for difficult small objects.
基金the support of the National Natural Science Foundation of China (Grant No.12304195)the Chutian Scholars Program in Hubei Province+3 种基金supported by the National Natural Science Foundation of China (Grant No.12074107)the program of outstanding young and middle-aged scientific and technological innovation team of colleges and universities in Hubei Province (Grant No.T2020001)the innovation group project of the Natural Science Foundation of Hubei Province of China (Grant No.2022CFA012)supported by the Postdoctoral Innovation Research Program in Hubei Province (Grant No.351342)。
文摘Disorder effects on topological materials in integer dimensions have been extensively explored in recent years. However, its influence on topological systems in fractional dimensions remains unclear. Here, we investigate the disorder effects on a fractal system constructed on the Sierpiński lattice in fractional dimensions. The system supports the second-order topological insulator phase characterized by a quantized quadrupole moment and the normal insulator phase. We find that the second-order topological insulator phase on the Sierpiński lattice is robust against weak disorder but suppressed by strong disorder. Most interestingly, we find that disorder can transform the normal insulator phase to the second-order topological insulator phase with an emergent quantized quadrupole moment. Finally, the disorder-induced phase is further confirmed by calculating the energy spectrum and the corresponding probability distributions.
