Ferromagnetism in moiréflat-band systems has been extensively studied in the first valence miniband of twisted MoTe_(2),while its controlled realization at higher moiréfillings remains largely unexplored,exc...Ferromagnetism in moiréflat-band systems has been extensively studied in the first valence miniband of twisted MoTe_(2),while its controlled realization at higher moiréfillings remains largely unexplored,except for very recent works reporting correlated magnetism near half filling of the second moiréband.Here,we investigate rhombohedral-stacked twisted MoTe_(2)/hBN/WSe_(2) heterostructures and uncover two distinct ferromagnetic(FM)regions:one centered near v_(h)≈3(half filling of the second moirévalence miniband)at zero displacement field,and a re-entrant FM phase that emerges for v_(h)>3 only under a finite out-of-plane electric field.These FM regions are separated by a narrow filling window with a strongly suppressed magnetic circular dichroism(MCD)response.Layer-sensitive exciton spectroscopy identifies that WSe_(2) is hole-doped in the re-entrant FM region,consistent with partial charge transfer from MoTe_(2) to WSe_(2).We propose that electric-field–induced layer repopulation stabilizes the re-entrant ferromagnetic phase by pinning the effective MoTe_(2) filling near v_(h)≈3 while adding carriers to the remote WSe_(2) layer.Our results demonstrate that remote-layer population control is an effective tuning knob for magnetic ordering in higher moiréminibands,extending the design space for correlated spin–valley phases in transition metal dichalcogenide heterostructures.展开更多
Tetralayer graphene has shown several interesting properties such as tunable Lifshitz transitions,helical edge states,and high-temperature anomalous Hall effects.The band structure,which directly relates to these phen...Tetralayer graphene has shown several interesting properties such as tunable Lifshitz transitions,helical edge states,and high-temperature anomalous Hall effects.The band structure,which directly relates to these phenomena,has so far been predominantly determined by fitting Landau-level spectra.Here,by characterizing the electronic capacitance,we reveal unprecedented details of its band structure:the energy shift between the heavy-and light-mass band edges in the conduction band is much larger than that in the valence band.Their responses to displacement fields are also distinct:while the former increases monotonically and significantly,the latter first decreases and then increases slightly.Our results suggest that the interlayer interactions and hopping parameters are more complex than previously expected,calling for precise measurements of band structures in various multilayer van der Waals systems.展开更多
Spin-orbit interaction(SOI)can be introduced by the proximity effect to modulate the electronic properties of graphene-based heterostructures.In this work,we stack trilayer WSe_(2) on Bernal tetralayer graphene to inv...Spin-orbit interaction(SOI)can be introduced by the proximity effect to modulate the electronic properties of graphene-based heterostructures.In this work,we stack trilayer WSe_(2) on Bernal tetralayer graphene to investigate the influence of SOI on the anomalous Hall effect(AHE).In this structurally asymmetric device,by comparing the magnitude of AHE at positive and negative displacement fields,we find that AHE is strongly enhanced by bringing electrons in proximity to the WSe_(2) layer.Meanwhile,the enhanced AHE signal persists up to 80 K,providing important routes for topological device applications at high temperatures.展开更多
Semiconductor moirésuperlattices provide great platforms for exploring exotic collective excitations.Optical Stark effect,a shift of the electronic transition in the presence of a light field,provides an ultrafas...Semiconductor moirésuperlattices provide great platforms for exploring exotic collective excitations.Optical Stark effect,a shift of the electronic transition in the presence of a light field,provides an ultrafast and coherent method of manipulating matter states,which,however,has not been demonstrated in moirématerials.Here,we report the valleyselective optical Stark effect of moiréexcitons in the WSe_(2)/WS_(2)superlattice by using transient reflection spectroscopy.Prominent valley-selective energy shifts up to 7.8 meV have been observed for moiréexcitons,corresponding to pseudomagnetic fields as large as 34 T.Our results provide a route to coherently manipulate exotic states in moirésuperlattices.展开更多
Reservoir computing has been considered as a promising intelligent computing paradigm for effectively processing complex temporal information.Exploiting tunable and reproducible dynamics in the single electronic devic...Reservoir computing has been considered as a promising intelligent computing paradigm for effectively processing complex temporal information.Exploiting tunable and reproducible dynamics in the single electronic device have been desired to implement the “reservoir” and the “readout” layer of reservoir computing system.Two-dimensional moiré materials,with an artificial lattice constant many times larger than the atomic length scale,are one type of most studied artificial quantum materials in community of material science and condensed-matter physics over the past years.These materials are featured with gate-tunable periodic potential and electronic correlation,thus varying the electric field allows the electrons in the moiré potential per unit cell to exhibit distinct and reproducible dynamics,showing great promise in robust reservoir computing.Here,we report that a moiré synaptic transistor can be used to implement the reservoir computing system with a homogeneous reservoir-readout architecture.The synaptic transistor is fabricated based on an h-BN/bilayer graphene/h-BN moiré heterostructure,exhibiting ferroelectricity-like hysteretic gate voltage dependence of resistance.Varying the magnitude of the gate voltage enables the moiré transistor to switch between long-term memory and shortterm memory with nonlinear dynamics.By employing the short-and long-term memories as the reservoir nodes and weights of the readout layer,respectively,we construct a full-moiré physical neural network and demonstrate that the classification accuracy of 90.8% can be achieved for the MNIST(Modified National Institute of Standards and Technology) handwritten digits database.Our work would pave the way towards the development of neuromorphic computing based on moiré materials.展开更多
Twisting two layers into a magic angle(MA) of ~1.1°is found essential to create low energy flat bands and the resulting correlated insulating,superconducting,and magnetic phases in twisted bilayer graphene(TBG).W...Twisting two layers into a magic angle(MA) of ~1.1°is found essential to create low energy flat bands and the resulting correlated insulating,superconducting,and magnetic phases in twisted bilayer graphene(TBG).While most of previous works focus on revealing these emergent states in MA-TBG,a study of the twist angle dependence,which helps to map an evolution of these phases,is yet less explored.Here,we report a magnetotransport study on one non-magic angle TBG device,whose twist angle θ changes from 1.25° at one end to 1.43°at the other.For θ=1.25° we observe an emergence of topological insulating states at hole side with a sequence of Chern number |C|=4-|v|,where v is the number of electrons(holes) in moire unite cell.When θ> 1.25°,the Chern insulator from flat band disappears and evolves into fractal Hofstadter butterfly quantum Hall insulator where magnetic flux in one moire unite cell matters.Our observations will stimulate further theoretical and experimental investigations on the relationship between electron interactions and non-trivial band topology.展开更多
When a perpendicular magnetic field penetrates a thin slab of a type-Ⅱ superconductor it produces vortices,with one vortex per flux quantum,h/2e.The vortices interact repulsively and form an ordered array(Abrikosov l...When a perpendicular magnetic field penetrates a thin slab of a type-Ⅱ superconductor it produces vortices,with one vortex per flux quantum,h/2e.The vortices interact repulsively and form an ordered array(Abrikosov lattice)in clean systems,while strong disorder changes the lattice into a vortex glass.The collective vortex dynamics is extremely vulnerable to external perturbations.Consequently,although of great importance,experimental observation is limited.Here we investigate type-Ⅱ superconducting films(PdBi_(2)and NbSe_(2))with surface acoustic waves(SAWs)at mK temperature.When sweeping the magnetic field at an extremely slow rate,we observe a series of spikes in the attenuation and velocity of the SAW,on average separated in field by approximately Hc1.We propose the following scenario:The vortex-free region at the edges of the film produces an edge barrier across which the vortices can enter or leave.When the applied field changes,the induced supercurrents flowing along this edge region lowers this barrier until there is an instability.At that point,vortices avalanche into(or out of)the bulk and change the vortex crystal,suggested by the sharp jump in each such spike.The vortices then gradually relax to a new stable pinned configuration,leading to a~30 s relaxation after the jump.Our observation enriches the limited experimental evidence on the important topic of real-time vortex dynamics in superconductors.展开更多
Twist,the very degree of freedom in van der Waals heterostructures,offers a compelling avenue to manipulate and tailor their electrical and optical characteristics.In particular,moirépatterns in twisted homobilay...Twist,the very degree of freedom in van der Waals heterostructures,offers a compelling avenue to manipulate and tailor their electrical and optical characteristics.In particular,moirépatterns in twisted homobilayer transition metal dichalcogenides(TMDs)lead to zone folding and miniband formation in the resulting electronic bands,holding the promise to exhibit inter-layer excitonic optical phenomena.Although some experiments have shown the existence of twist-angle-dependent intra-and inter-layer excitons in twisted MoSe2 homobilayers,electrical control of the interlayer excitons in MoSe_(2) is relatively under-explored.Here,we show the signatures of the moiréeffect on intralayer and interlayer excitons in 2H-stacked twisted MoSe2 homobilayers.Doping-and electric field-dependent photoluminescence mea-surements at low temperatures give evidence of the momentum-direct K-K intralayer excitons,and the momentum-indirect Г-K and Г-Q interlayer excitons.Our results suggest that twisted MoSe_(2) homobilayers are an intriguing platform for engineering interlayer exciton states,which may shed light on future atomically thin optoelectronic applications.展开更多
Moiré superlattices in van der Waals heterostructures have recently attracted enormous interests, due to the highly controllable electronic correlation that gives rise to superconductivity, ferromagnetism, and no...Moiré superlattices in van der Waals heterostructures have recently attracted enormous interests, due to the highly controllable electronic correlation that gives rise to superconductivity, ferromagnetism, and nontrivial topological properties. To gain a deep understanding of such exotic properties, it is essential to clarify the broken symmetry between spin and valley flavors which universally exists in these ground states. Here in a rhombohedral trilayer graphene crystallographically aligned with a hexagonal boron nitride, we report various kinds of symmetry-breaking transition tuned by displacement fields(D) and magnetic fields:(ⅰ) While it is well known that a finite D can enhance correlation to result in correlated insulators at fractional fillings of a flat band, we find the correlation gap emerges before the flavor is fully filled at a positive D, but the sequence is reversed at a negative D.(ⅱ) Around zero D, electronic correlation can be invoked by narrow Landau levels, leading to quantum Hall ferromagnetism that lifts all the degeneracies including not only spin and valley but also orbital degrees of freedom. Our result unveils the complication of transitions between symmetry-breaking phases, shedding light on the mechanisms of various exotic phenomena in strongly correlated systems.展开更多
Transition metal dichalcogenides(TMDs),being valley selectively,are an ideal system hosting excitons.Stacking TMDs together to form heterostructure offers an exciting platform to engineer new optical and electronic pr...Transition metal dichalcogenides(TMDs),being valley selectively,are an ideal system hosting excitons.Stacking TMDs together to form heterostructure offers an exciting platform to engineer new optical and electronic properties in solid-state systems.However,due to the limited accuracy and repetitiveness of sample preparation,the effects of interlayer coupling on the electronic and excitonic properties have not been systematically investigated.In this report,we study the photoluminescence spectra of bilayer-bilayer MoS_(2)/WS_(2) heterostructure with a typeⅡband alignment.We demonstrate that thermal annealing can increase interlayer coupling in the van der Waals heterostructures,and after thermally induced band hybridization such heterostructure behaves more like an artificial new solid,rather than just the combination of two individual TMD components.We also carry out experimental and theoretical studies of the electric controllable direct and indirect infrared interlayer excitons in such system.Our study reveals the impact of interlayer coupling on interlayer excitons and will shed light on the understanding and engineering of layer-controlled spin-valley configuration in twisted van der Waals heterostructures.展开更多
Unraveling the mechanism underlying topological phases, notably the Chern insulators(Ch Is) in strong correlated systems at the microscopy scale, has captivated significant research interest. Nonetheless, Ch Is harbor...Unraveling the mechanism underlying topological phases, notably the Chern insulators(Ch Is) in strong correlated systems at the microscopy scale, has captivated significant research interest. Nonetheless, Ch Is harboring topological information have not always manifested themselves, owing to the constraints imposed by displacement fields in certain experimental configurations. In this study, we employ density-tuned scanning tunneling microscopy(DT-STM) to investigate the Ch Is in twisted monolayer–bilayer graphene(t MBG). At zero magnetic field, we observe correlated metallic states.While under a magnetic field, a metal–insulator transition happens and an integer Ch I is formed emanating from the filling index s = 3 with a Chern number C = 1. Our results underscore the pivotal role of magnetic fields as a powerful probe for elucidating topological phases in twisted Van der Waals heterostructures.展开更多
Magnetoresistance(MR) provides rich information about Fermi surface, carrier scatterings, and exotic phases for a given electronic system. Here, we report a study of the magnetoresistance for the metallic states in tw...Magnetoresistance(MR) provides rich information about Fermi surface, carrier scatterings, and exotic phases for a given electronic system. Here, we report a study of the magnetoresistance for the metallic states in twisted double bilayer graphene(TDBG). We observe quadratic magnetoresistance in both Moiré valence band(VB) and Moiré conduction band(CB). The scaling analysis shows validity of Kohler's rule in the Moiré valence band. On the other hand, the quadratic magnetoresistance appears near the halo structure in the Moiré conduction band, and it violates Kohler's rule, demonstrating the MR scaling related to band structure in TDBG. We also propose an alternative scaling near the halo structure. Further analysis implies that the observed quadratic magnetoresistance and alternative scaling in conduction band are related to the halo boundary. Our results may inspire investigation on MR in twisted 2D materials and provide new knowledge for MR study in condensed matter physics.展开更多
Transferring high-quality exfoliated graphene flakes onto different substrates while keeping the graphene free of polymer residues is of great importance, but at the same time very challenging. Currently, the only fea...Transferring high-quality exfoliated graphene flakes onto different substrates while keeping the graphene free of polymer residues is of great importance, but at the same time very challenging. Currently, the only feasible way is the so-called all-dry "pick-and-lift" method, in which a hexagonal boron nitride(hBN) flake is employed to serve as a stamp to pick up graphene from one substrate and to lift it down onto another substrate. The transferred graphene samples, however,are always covered or encapsulated by hBN flakes, which leads to difficulties in further characterizations. Here, we report an improved "pick-and-lift" method, which allows ultra-clean graphene flakes to be transferred onto a variety of substrates without hBN coverage. Basically, by exploiting the superlubricity at the graphene/hBN stack interface, we are able to remove the top-layer hBN stamp by applying a tangential force and expose the underneath graphene.展开更多
The graphene-based moiré superlattice has been demonstrated as an exciting system for investigating strong correlation phenomenon. However, the fabrication of such moiré superlattice mainly relies on transfe...The graphene-based moiré superlattice has been demonstrated as an exciting system for investigating strong correlation phenomenon. However, the fabrication of such moiré superlattice mainly relies on transfer technology. Here, we report the epitaxial growth of trilayer graphene(TLG) moiré superlattice on hexagonal boron nitride(h BN) by a remote plasma-enhanced chemical vapor deposition method. The as-grown TLG/h BN shows a uniform moiré pattern with a period of ~ 15 nm by atomic force microscopy(AFM) imaging, which agrees with the lattice mismatch between graphene and h BN. By fabricating the device with both top and bottom gates, we observed a gate-tunable bandgap at charge neutral point(CNP) and displacement field tunable satellite resistance peaks at half and full fillings. The resistance peak at half-filling indicates a strong electron–electron correlation in our grown TLG/h BN superlattice. In addition, we observed quantum Hall states at Landau level filling factors ν = 6, 10, 14,..., indicating that our grown trilayer graphene has the ABC stacking order. Our work suggests that epitaxy provides an easy way to fabricate stable and reproducible two-dimensional strongly correlated electronic materials.展开更多
Twisted bilayer graphene heterostructures have recently emerged as a well-established platform for studying strongly correlated phases,such as correlated insulating,superconducting,and topological states.Extending thi...Twisted bilayer graphene heterostructures have recently emerged as a well-established platform for studying strongly correlated phases,such as correlated insulating,superconducting,and topological states.Extending this notion to twisted multilayer graphene heterostructures has exhibited more diverse correlated phases,as some fundamental properties related to symmetry and band structures are correspondingly modified.Here,we report the observations of correlated states in twisted monolayer-trilayer(Bernal stacked)graphene heterostructures.Correlated phases at integer fillings of the moire unit cell are revealed at a high displacement field and stabilized with a moderate magnetic field on the electron-doping side at a twist angle of 1.45°,where the lift of degeneracy at the integer fillings is observed in the Landau fan diagram.Our results demonstrate the effectiveness of moire engineering in an extended structure and provide insights into electric-field tunable correlated phases.展开更多
Twisted graphene systems with flat bands have attracted much attention for they are excellent platforms to research novel quantum phases. Recently, transport measurements about twisted monolayer–bilayer graphene(t MB...Twisted graphene systems with flat bands have attracted much attention for they are excellent platforms to research novel quantum phases. Recently, transport measurements about twisted monolayer–bilayer graphene(t MBG) have shown the existence of correlated states and topological states in this system. However, the direct observations of the band structures and the corresponding spatial distributions are still not sufficient. Here we show that the distributions of flat bands in t MBG host two different modes by scanning tunneling microscopy and spectroscopy(STM/S). By tuning our t MBG device from the empty filling state to the full filling state through the back gate, we observe that the distributions of two flat bands develop from localized mode to delocalized mode. This gate-controlled flat band wavefunction polarization is unique to the t MBG system. Our work suggests that t MBG is promising to simulate both twisted bilayer graphene(TBG) and twisted double bilayer graphene(t DBG) and would be an ideal platform to explore novel moiré physics.展开更多
Moiré superlattices have emerged as a highly controllable quantum platform for exploration of various fascinating phenomena,such as Mott insulator states,ferroelectric order,unconventional superconductivity and o...Moiré superlattices have emerged as a highly controllable quantum platform for exploration of various fascinating phenomena,such as Mott insulator states,ferroelectric order,unconventional superconductivity and orbital ferromagnetism.Although remarkable progress has been achieved,current research in moiré physics has mainly focused on the single species properties,while the coupling between distinct moiré quantum phenomena remains elusive.Here we demonstrate,for the first time,the strong coupling between ferroelectricity and correlated states in a twisted quadrilayer MoS2moiré superlattice,where the twist angles are controlled in sequence to be ~57°,~0°,and ~-57°.Correlated insulator states are unambiguously established at moiré band filling factors v = 1,2,3 of twisted quadrilayer MoS_(2).Remarkably,ferroelectric order can occur at correlated insulator states and disappears quickly as the moiré band filling deviates from the integer fillings,providing smoking gun evidences of the coupling between ferroelectricity and correlated states.Our results demonstrate the coupling between different moiré quantum properties and will hold great promise for new moiré physics and applications.展开更多
世界卫生组织计划在"国际疾病分类第11版(International Classification of Diseases-11,ICD-11)"中加入"传统医学"这一部分,预期的版本是"传统医学国际分类-中日韩三国版"。传统医学加入ICD-11,有非常...世界卫生组织计划在"国际疾病分类第11版(International Classification of Diseases-11,ICD-11)"中加入"传统医学"这一部分,预期的版本是"传统医学国际分类-中日韩三国版"。传统医学加入ICD-11,有非常重大深远的意义。传统医学的国际分类的建立,不仅有利于传统医学,也有利于西方医学。所以,中、日、韩三国必须充分理解这个项目的意义和难得的现实机遇,相互进行密切合作来实现这一目标。展开更多
AIM: To evaluate the clinical utility of hepatic clearance(HC) measured with technetium-99m-diethylenetriaminepenta-acetic acid-galactosyl human serum albumin(99mTc-GSA) single-photon emission computed tomography(SPEC...AIM: To evaluate the clinical utility of hepatic clearance(HC) measured with technetium-99m-diethylenetriaminepenta-acetic acid-galactosyl human serum albumin(99mTc-GSA) single-photon emission computed tomography(SPECT) to estimate the degree of liver fibrosis.METHODS:Seventy-eight consecutive patients who underwent initial hepatectomy due to hepatocellular carcinoma were enrolled in this study.Indocyanine green clearance(ICG R15),quantitative indices estimated by 99mTc-GSA[the receptor index(LHL15 and HH15)and HC via SPECT analysis],and conventional liver function tests were performed before hepatectomy.Correlations among the quantitative indices for liver functional reserve,conventional liver function tests,andthe degree of liver fibrosis were evaluated.RESULTS:The degree of liver fibrosis was correlated with ICG R15,HH15,LHL15,and HC.HC showed the best correlation with conventional liver function tests.According to multivariate analysis,HC and LHL15 were significant independent predictors of severe fibrosis.HC was the most valuable index for predicting severe fibrosis.CONCLUSION:HC measured with 99mTc-GSA SPECT is a reliable index for assessing liver fibrosis before hepatectomy.展开更多
BACKGROUND We recently reported on a hereditary enteropathy associated with a gene encoding a prostaglandin transporter and referred to as chronic enteropathy associated with SLCO2 A1 gene(CEAS).Crohn's disease(CD...BACKGROUND We recently reported on a hereditary enteropathy associated with a gene encoding a prostaglandin transporter and referred to as chronic enteropathy associated with SLCO2 A1 gene(CEAS).Crohn's disease(CD)is a major differential diagnosis of CEAS,because these diseases share some clinical features.Therefore,there is a need to develop a convenient screening test to distinguish CEAS from CD.AIM To examine whether prostaglandin E major urinary metabolites(PGE-MUM)can serve as a biomarker to distinguish CEAS from CD.METHODS This was a transactional study of 20 patients with CEAS and 98 patients with CD.CEAS was diagnosed by the confirmation of homozygous or compound heterozygous mutation of SLCO2 A1.We measured the concentration of PGEMUM in spot urine by radioimmunoassay,and the concentration was compared between the two groups of patients.We also determined the optimal cut-off value of PGE-MUM to distinguish CEAS from CD by receiver operating characteristic(ROC)curve analysis.RESULTS Twenty Japanese patients with CEAS and 98 patients with CD were enrolled.PGE-MUM concentration in patients with CEAS was significantly higher than that in patients with CD(median 102.7 vs 27.9μg/g×Cre,P<0.0001).One log unit increase in PGE-MUM contributed to 7.3 increase in the likelihood for the diagnosis of CEAS[95%confidence interval(CI)3.2-16.7].A logistic regression analysis revealed that the association was significant even after adjusting confounding factors(adjusted odds ratio 29.6,95%CI 4.7-185.7).ROC curve analysis revealed the optimal PGE-MUM cut-off value for the distinction of CEAS from CD to be 48.9μg/g×Cre with 95.0%sensitivity and 79.6%specificity.CONCLUSION PGE-MUM measurement is a convenient,non-invasive and useful test for the distinction of CEAS from CD.展开更多
基金supported by the National Key R&D Program of China(Grant Nos.2021YFA1400100 and 2021YFA1401400)the National Natural Science Foundation of China(Grant Nos.12550403,12174250 and 12141404)+2 种基金the Shanghai Jiao Tong University 2030 Initiative Program B(Grant No.WH510207202)support from JSPS KAKENHI(Grant Nos.21H05233 and 23H02052)the World Premier International Research Center Initiative(WPI),MEXT,Japan。
文摘Ferromagnetism in moiréflat-band systems has been extensively studied in the first valence miniband of twisted MoTe_(2),while its controlled realization at higher moiréfillings remains largely unexplored,except for very recent works reporting correlated magnetism near half filling of the second moiréband.Here,we investigate rhombohedral-stacked twisted MoTe_(2)/hBN/WSe_(2) heterostructures and uncover two distinct ferromagnetic(FM)regions:one centered near v_(h)≈3(half filling of the second moirévalence miniband)at zero displacement field,and a re-entrant FM phase that emerges for v_(h)>3 only under a finite out-of-plane electric field.These FM regions are separated by a narrow filling window with a strongly suppressed magnetic circular dichroism(MCD)response.Layer-sensitive exciton spectroscopy identifies that WSe_(2) is hole-doped in the re-entrant FM region,consistent with partial charge transfer from MoTe_(2) to WSe_(2).We propose that electric-field–induced layer repopulation stabilizes the re-entrant ferromagnetic phase by pinning the effective MoTe_(2) filling near v_(h)≈3 while adding carriers to the remote WSe_(2) layer.Our results demonstrate that remote-layer population control is an effective tuning knob for magnetic ordering in higher moiréminibands,extending the design space for correlated spin–valley phases in transition metal dichalcogenide heterostructures.
基金supported by the National Natural Science Foundation of China(Grant Nos.123B1037 and 12274402)the National Key Research and Development Program of China(Grant No.2024YFA1409700).
文摘Tetralayer graphene has shown several interesting properties such as tunable Lifshitz transitions,helical edge states,and high-temperature anomalous Hall effects.The band structure,which directly relates to these phenomena,has so far been predominantly determined by fitting Landau-level spectra.Here,by characterizing the electronic capacitance,we reveal unprecedented details of its band structure:the energy shift between the heavy-and light-mass band edges in the conduction band is much larger than that in the valence band.Their responses to displacement fields are also distinct:while the former increases monotonically and significantly,the latter first decreases and then increases slightly.Our results suggest that the interlayer interactions and hopping parameters are more complex than previously expected,calling for precise measurements of band structures in various multilayer van der Waals systems.
基金Project supported by the National Key R&D Program of China(Grant Nos.2021YFA1400100 and 2024YFA1409700)the National Natural Science Foudation of China(Grant Nos.12374168 and T2325026)。
文摘Spin-orbit interaction(SOI)can be introduced by the proximity effect to modulate the electronic properties of graphene-based heterostructures.In this work,we stack trilayer WSe_(2) on Bernal tetralayer graphene to investigate the influence of SOI on the anomalous Hall effect(AHE).In this structurally asymmetric device,by comparing the magnitude of AHE at positive and negative displacement fields,we find that AHE is strongly enhanced by bringing electrons in proximity to the WSe_(2) layer.Meanwhile,the enhanced AHE signal persists up to 80 K,providing important routes for topological device applications at high temperatures.
基金Project supported by the National Key R&D Program of China(Grant Nos.2022YFA1402400 and 2022YFA1405400)the National Natural Science Foundation of China(Grant Nos.11934011 and 12274365)+3 种基金Zhejiang Provincial Natural Science Foundation of China(Grant No.LR24A040001)Open project of Key Laboratory of Artificial Structures and Quantum Control(Ministry of Education)of Shanghai Jiao Tong Universitysupport from the JSPS KAKENHI(Grant Nos.20H00354 and 23H02052)World Premier International Research Center Initiative(WPI),MEXT,Japan。
文摘Semiconductor moirésuperlattices provide great platforms for exploring exotic collective excitations.Optical Stark effect,a shift of the electronic transition in the presence of a light field,provides an ultrafast and coherent method of manipulating matter states,which,however,has not been demonstrated in moirématerials.Here,we report the valleyselective optical Stark effect of moiréexcitons in the WSe_(2)/WS_(2)superlattice by using transient reflection spectroscopy.Prominent valley-selective energy shifts up to 7.8 meV have been observed for moiréexcitons,corresponding to pseudomagnetic fields as large as 34 T.Our results provide a route to coherently manipulate exotic states in moirésuperlattices.
基金supported in part by the National Natural Science Foundation of China(Grant Nos.62122036,12322407,62034004,61921005,12074176,and 61974176)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB44000000)+1 种基金the Fundamental Research Funds for the Central Universities(Grant Nos.020414380203 and 020414380179)the support from the AIQ foundation。
文摘Reservoir computing has been considered as a promising intelligent computing paradigm for effectively processing complex temporal information.Exploiting tunable and reproducible dynamics in the single electronic device have been desired to implement the “reservoir” and the “readout” layer of reservoir computing system.Two-dimensional moiré materials,with an artificial lattice constant many times larger than the atomic length scale,are one type of most studied artificial quantum materials in community of material science and condensed-matter physics over the past years.These materials are featured with gate-tunable periodic potential and electronic correlation,thus varying the electric field allows the electrons in the moiré potential per unit cell to exhibit distinct and reproducible dynamics,showing great promise in robust reservoir computing.Here,we report that a moiré synaptic transistor can be used to implement the reservoir computing system with a homogeneous reservoir-readout architecture.The synaptic transistor is fabricated based on an h-BN/bilayer graphene/h-BN moiré heterostructure,exhibiting ferroelectricity-like hysteretic gate voltage dependence of resistance.Varying the magnitude of the gate voltage enables the moiré transistor to switch between long-term memory and shortterm memory with nonlinear dynamics.By employing the short-and long-term memories as the reservoir nodes and weights of the readout layer,respectively,we construct a full-moiré physical neural network and demonstrate that the classification accuracy of 90.8% can be achieved for the MNIST(Modified National Institute of Standards and Technology) handwritten digits database.Our work would pave the way towards the development of neuromorphic computing based on moiré materials.
基金National Key R&D program(Grant No.2020YFA0309604)the National Natural Science Foundation of China(Grant Nos.61888102,11834017,and 12074413)+7 种基金the Strategic Priority Research Program of CAS(Grant Nos.XDB30000000 and XDB33000000)the Key-Area Research and Development Program of Guangdong Province(Grant No.2020B0101340001)Research Program of Beijing Academy of Quantum Information Sciences(Grant No.Y18G11)the start-up grant of ShanghaiTech UniversityNational Key R&D Program(Grant No.2020YFA0309601)Elemental Strategy Initiative conducted by the MEXT,Japan(Grant No.JPMXP0112101001)JSPS KAKENHI(Grant No.JP20H00354)CREST(JPMJCR15F3),JST。
文摘Twisting two layers into a magic angle(MA) of ~1.1°is found essential to create low energy flat bands and the resulting correlated insulating,superconducting,and magnetic phases in twisted bilayer graphene(TBG).While most of previous works focus on revealing these emergent states in MA-TBG,a study of the twist angle dependence,which helps to map an evolution of these phases,is yet less explored.Here,we report a magnetotransport study on one non-magic angle TBG device,whose twist angle θ changes from 1.25° at one end to 1.43°at the other.For θ=1.25° we observe an emergence of topological insulating states at hole side with a sequence of Chern number |C|=4-|v|,where v is the number of electrons(holes) in moire unite cell.When θ> 1.25°,the Chern insulator from flat band disappears and evolves into fractal Hofstadter butterfly quantum Hall insulator where magnetic flux in one moire unite cell matters.Our observations will stimulate further theoretical and experimental investigations on the relationship between electron interactions and non-trivial band topology.
基金supported by the National Key Research Program of China(Grant Nos.2021YFA1401900,2022YFA1403300,and 2020YFA0309100)the Innovation Program for Quantum Science and Technology(Grant Nos.2021ZD0302602 and 2024ZD0300103)+1 种基金the National Natural Science Foundation of China(Grant No.12074073)for samplefabrication and measurementthe support by the The Basic Research Program of the Chinese Academy of Sciences Based on Major Scientific Infrastructures(Grant No.JZHKYPT-2021-08).
文摘When a perpendicular magnetic field penetrates a thin slab of a type-Ⅱ superconductor it produces vortices,with one vortex per flux quantum,h/2e.The vortices interact repulsively and form an ordered array(Abrikosov lattice)in clean systems,while strong disorder changes the lattice into a vortex glass.The collective vortex dynamics is extremely vulnerable to external perturbations.Consequently,although of great importance,experimental observation is limited.Here we investigate type-Ⅱ superconducting films(PdBi_(2)and NbSe_(2))with surface acoustic waves(SAWs)at mK temperature.When sweeping the magnetic field at an extremely slow rate,we observe a series of spikes in the attenuation and velocity of the SAW,on average separated in field by approximately Hc1.We propose the following scenario:The vortex-free region at the edges of the film produces an edge barrier across which the vortices can enter or leave.When the applied field changes,the induced supercurrents flowing along this edge region lowers this barrier until there is an instability.At that point,vortices avalanche into(or out of)the bulk and change the vortex crystal,suggested by the sharp jump in each such spike.The vortices then gradually relax to a new stable pinned configuration,leading to a~30 s relaxation after the jump.Our observation enriches the limited experimental evidence on the important topic of real-time vortex dynamics in superconductors.
基金supported by the National Key R&D Program of China(No.2023YFF1500600)the National Natural Science Foun-dation of China(Nos.12004259,12204287)+3 种基金China Postdoc-toral Science Foundation(Grant No.2022M723215)Zheng Vitto Han acknowledges the support of the Fund for Shanxi“1331 Project”Key Subjects Construction,and the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302003)Kenji Watanabe and Takashi Taniguchi acknowledge support from the JSPS KAKENHI(Grant Nos.20H00354 and 23H02052)the World Premier International Research Center Initiative(WPI),MEXT,Japan.
文摘Twist,the very degree of freedom in van der Waals heterostructures,offers a compelling avenue to manipulate and tailor their electrical and optical characteristics.In particular,moirépatterns in twisted homobilayer transition metal dichalcogenides(TMDs)lead to zone folding and miniband formation in the resulting electronic bands,holding the promise to exhibit inter-layer excitonic optical phenomena.Although some experiments have shown the existence of twist-angle-dependent intra-and inter-layer excitons in twisted MoSe2 homobilayers,electrical control of the interlayer excitons in MoSe_(2) is relatively under-explored.Here,we show the signatures of the moiréeffect on intralayer and interlayer excitons in 2H-stacked twisted MoSe2 homobilayers.Doping-and electric field-dependent photoluminescence mea-surements at low temperatures give evidence of the momentum-direct K-K intralayer excitons,and the momentum-indirect Г-K and Г-Q interlayer excitons.Our results suggest that twisted MoSe_(2) homobilayers are an intriguing platform for engineering interlayer exciton states,which may shed light on future atomically thin optoelectronic applications.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11974027 and 62275265)the National Key Research and Development Program of China (Grant Nos. 2019YFA0307800 and 2021YFA1400100)Beijing Natural Science Foundation (Grant Nos. Z190011 and 4222084)。
文摘Moiré superlattices in van der Waals heterostructures have recently attracted enormous interests, due to the highly controllable electronic correlation that gives rise to superconductivity, ferromagnetism, and nontrivial topological properties. To gain a deep understanding of such exotic properties, it is essential to clarify the broken symmetry between spin and valley flavors which universally exists in these ground states. Here in a rhombohedral trilayer graphene crystallographically aligned with a hexagonal boron nitride, we report various kinds of symmetry-breaking transition tuned by displacement fields(D) and magnetic fields:(ⅰ) While it is well known that a finite D can enhance correlation to result in correlated insulators at fractional fillings of a flat band, we find the correlation gap emerges before the flavor is fully filled at a positive D, but the sequence is reversed at a negative D.(ⅱ) Around zero D, electronic correlation can be invoked by narrow Landau levels, leading to quantum Hall ferromagnetism that lifts all the degeneracies including not only spin and valley but also orbital degrees of freedom. Our result unveils the complication of transitions between symmetry-breaking phases, shedding light on the mechanisms of various exotic phenomena in strongly correlated systems.
基金the National Key Research and Development Program of China(Grant No.2020YFA0309604)the National Natural Science Foundation of China(Grant Nos.11834017,61888102,and 12074413)+2 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB30000000 and XDB33000000)the Key-Area Research and Development Program of Guangdong Province,China(Grant No.2020B0101340001)the Research Program of Beijing Academy of Quantum Information Sciences(Grant No.Y18G11).
文摘Transition metal dichalcogenides(TMDs),being valley selectively,are an ideal system hosting excitons.Stacking TMDs together to form heterostructure offers an exciting platform to engineer new optical and electronic properties in solid-state systems.However,due to the limited accuracy and repetitiveness of sample preparation,the effects of interlayer coupling on the electronic and excitonic properties have not been systematically investigated.In this report,we study the photoluminescence spectra of bilayer-bilayer MoS_(2)/WS_(2) heterostructure with a typeⅡband alignment.We demonstrate that thermal annealing can increase interlayer coupling in the van der Waals heterostructures,and after thermally induced band hybridization such heterostructure behaves more like an artificial new solid,rather than just the combination of two individual TMD components.We also carry out experimental and theoretical studies of the electric controllable direct and indirect infrared interlayer excitons in such system.Our study reveals the impact of interlayer coupling on interlayer excitons and will shed light on the understanding and engineering of layer-controlled spin-valley configuration in twisted van der Waals heterostructures.
文摘Unraveling the mechanism underlying topological phases, notably the Chern insulators(Ch Is) in strong correlated systems at the microscopy scale, has captivated significant research interest. Nonetheless, Ch Is harboring topological information have not always manifested themselves, owing to the constraints imposed by displacement fields in certain experimental configurations. In this study, we employ density-tuned scanning tunneling microscopy(DT-STM) to investigate the Ch Is in twisted monolayer–bilayer graphene(t MBG). At zero magnetic field, we observe correlated metallic states.While under a magnetic field, a metal–insulator transition happens and an integer Ch I is formed emanating from the filling index s = 3 with a Chern number C = 1. Our results underscore the pivotal role of magnetic fields as a powerful probe for elucidating topological phases in twisted Van der Waals heterostructures.
基金supported by the National Key Research and Development Program of China (Grant No. 2020YFA0309600)the National Natural Science Foundation of China (Grant Nos. 61888102, 11834017, and 12074413)+3 种基金the Strategic Priority Research Program of CAS (Grant Nos. XDB30000000 and XDB33000000)the Key-Area Research and Development Program of Guangdong Province (Grant No. 2020B0101340001)supported by the Elemental Strategy Initiative conducted by the MEXT, Japan, Grant Number JPMXP0112101001, JSPS KAKENHI (Grant No. JP20H00354)A3 Foresight by JSPS。
文摘Magnetoresistance(MR) provides rich information about Fermi surface, carrier scatterings, and exotic phases for a given electronic system. Here, we report a study of the magnetoresistance for the metallic states in twisted double bilayer graphene(TDBG). We observe quadratic magnetoresistance in both Moiré valence band(VB) and Moiré conduction band(CB). The scaling analysis shows validity of Kohler's rule in the Moiré valence band. On the other hand, the quadratic magnetoresistance appears near the halo structure in the Moiré conduction band, and it violates Kohler's rule, demonstrating the MR scaling related to band structure in TDBG. We also propose an alternative scaling near the halo structure. Further analysis implies that the observed quadratic magnetoresistance and alternative scaling in conduction band are related to the halo boundary. Our results may inspire investigation on MR in twisted 2D materials and provide new knowledge for MR study in condensed matter physics.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFA0302001)the National Natural Science Foundation of China(Grant Nos.11574204 and 11774224)
文摘Transferring high-quality exfoliated graphene flakes onto different substrates while keeping the graphene free of polymer residues is of great importance, but at the same time very challenging. Currently, the only feasible way is the so-called all-dry "pick-and-lift" method, in which a hexagonal boron nitride(hBN) flake is employed to serve as a stamp to pick up graphene from one substrate and to lift it down onto another substrate. The transferred graphene samples, however,are always covered or encapsulated by hBN flakes, which leads to difficulties in further characterizations. Here, we report an improved "pick-and-lift" method, which allows ultra-clean graphene flakes to be transferred onto a variety of substrates without hBN coverage. Basically, by exploiting the superlubricity at the graphene/hBN stack interface, we are able to remove the top-layer hBN stamp by applying a tangential force and expose the underneath graphene.
基金Project supported by the National Key Research and Development Program of China (Grant No. 2020YFA0309600)the National Natural Science Foundation of China (Grant Nos. 61888102, 11834017, and 12074413)+3 种基金the Strategic Priority Research Program of CAS (Grant Nos. XDB30000000 and XDB33000000)the Key-Area Research and Development Program of Guangdong Province, China (Grant No. 2020B0101340001)support from the Elemental Strategy Initiative conducted by the MEXT, Japan (Grant No. JPMXP0112101001)JSPS KAKENHI (Grant Nos. 19H05790, 20H00354, and 21H05233), and A3 Foresight by JSPS
文摘The graphene-based moiré superlattice has been demonstrated as an exciting system for investigating strong correlation phenomenon. However, the fabrication of such moiré superlattice mainly relies on transfer technology. Here, we report the epitaxial growth of trilayer graphene(TLG) moiré superlattice on hexagonal boron nitride(h BN) by a remote plasma-enhanced chemical vapor deposition method. The as-grown TLG/h BN shows a uniform moiré pattern with a period of ~ 15 nm by atomic force microscopy(AFM) imaging, which agrees with the lattice mismatch between graphene and h BN. By fabricating the device with both top and bottom gates, we observed a gate-tunable bandgap at charge neutral point(CNP) and displacement field tunable satellite resistance peaks at half and full fillings. The resistance peak at half-filling indicates a strong electron–electron correlation in our grown TLG/h BN superlattice. In addition, we observed quantum Hall states at Landau level filling factors ν = 6, 10, 14,..., indicating that our grown trilayer graphene has the ABC stacking order. Our work suggests that epitaxy provides an easy way to fabricate stable and reproducible two-dimensional strongly correlated electronic materials.
基金the National Key R&D Program of China(Grant No.2019YFA0307800,J.M.)Beijing Natural Science Foundation(Grant No.Z190011,J.M.)+1 种基金the National Natural Science Foundation of China(Grant Nos.11974347,J.M.and 12204479,Z.Z.)Fundamental Research Funds for the Central Universities(J.M.)。
文摘Twisted bilayer graphene heterostructures have recently emerged as a well-established platform for studying strongly correlated phases,such as correlated insulating,superconducting,and topological states.Extending this notion to twisted multilayer graphene heterostructures has exhibited more diverse correlated phases,as some fundamental properties related to symmetry and band structures are correspondingly modified.Here,we report the observations of correlated states in twisted monolayer-trilayer(Bernal stacked)graphene heterostructures.Correlated phases at integer fillings of the moire unit cell are revealed at a high displacement field and stabilized with a moderate magnetic field on the electron-doping side at a twist angle of 1.45°,where the lift of degeneracy at the integer fillings is observed in the Landau fan diagram.Our results demonstrate the effectiveness of moire engineering in an extended structure and provide insights into electric-field tunable correlated phases.
基金support from the National Key R&D Program of China (Grant No. 2019YFA0307800)Beijing Natural Science Foundation (Grant No. Z190011)+1 种基金the National Natural Science Foundation of China (Grant No. 11974347)Fundamental Research Funds for the Central Universities。
文摘Twisted graphene systems with flat bands have attracted much attention for they are excellent platforms to research novel quantum phases. Recently, transport measurements about twisted monolayer–bilayer graphene(t MBG) have shown the existence of correlated states and topological states in this system. However, the direct observations of the band structures and the corresponding spatial distributions are still not sufficient. Here we show that the distributions of flat bands in t MBG host two different modes by scanning tunneling microscopy and spectroscopy(STM/S). By tuning our t MBG device from the empty filling state to the full filling state through the back gate, we observe that the distributions of two flat bands develop from localized mode to delocalized mode. This gate-controlled flat band wavefunction polarization is unique to the t MBG system. Our work suggests that t MBG is promising to simulate both twisted bilayer graphene(TBG) and twisted double bilayer graphene(t DBG) and would be an ideal platform to explore novel moiré physics.
基金supported by the Key-Area Research and Development Program of Guangdong Province,China (Grant No.2020B0101340001)the National Key Research and Development Program of China (Grant Nos.2021YFA1202900 and 2020YFA0309600)+4 种基金the National Science Foundation of China (Grant Nos.61888102,11834017,1207441,and 12274447)the Strategic Priority Research Program of CAS(Grant Nos.XDB30000000 and XDB33000000)the supports from the Elemental Strategy Initiative conducted by the MEXT,Japan(Grant No.JPMXP0112101001)JSPS KAKENHI(Grant Nos.19H05790,20H00354,and 21H05233)A3 Foresight by JSPS。
文摘Moiré superlattices have emerged as a highly controllable quantum platform for exploration of various fascinating phenomena,such as Mott insulator states,ferroelectric order,unconventional superconductivity and orbital ferromagnetism.Although remarkable progress has been achieved,current research in moiré physics has mainly focused on the single species properties,while the coupling between distinct moiré quantum phenomena remains elusive.Here we demonstrate,for the first time,the strong coupling between ferroelectricity and correlated states in a twisted quadrilayer MoS2moiré superlattice,where the twist angles are controlled in sequence to be ~57°,~0°,and ~-57°.Correlated insulator states are unambiguously established at moiré band filling factors v = 1,2,3 of twisted quadrilayer MoS_(2).Remarkably,ferroelectric order can occur at correlated insulator states and disappears quickly as the moiré band filling deviates from the integer fillings,providing smoking gun evidences of the coupling between ferroelectricity and correlated states.Our results demonstrate the coupling between different moiré quantum properties and will hold great promise for new moiré physics and applications.
基金supported by Japan Ministry of Health,Labour and Welfare Science Research Grant for FY 2007/2008
文摘世界卫生组织计划在"国际疾病分类第11版(International Classification of Diseases-11,ICD-11)"中加入"传统医学"这一部分,预期的版本是"传统医学国际分类-中日韩三国版"。传统医学加入ICD-11,有非常重大深远的意义。传统医学的国际分类的建立,不仅有利于传统医学,也有利于西方医学。所以,中、日、韩三国必须充分理解这个项目的意义和难得的现实机遇,相互进行密切合作来实现这一目标。
文摘AIM: To evaluate the clinical utility of hepatic clearance(HC) measured with technetium-99m-diethylenetriaminepenta-acetic acid-galactosyl human serum albumin(99mTc-GSA) single-photon emission computed tomography(SPECT) to estimate the degree of liver fibrosis.METHODS:Seventy-eight consecutive patients who underwent initial hepatectomy due to hepatocellular carcinoma were enrolled in this study.Indocyanine green clearance(ICG R15),quantitative indices estimated by 99mTc-GSA[the receptor index(LHL15 and HH15)and HC via SPECT analysis],and conventional liver function tests were performed before hepatectomy.Correlations among the quantitative indices for liver functional reserve,conventional liver function tests,andthe degree of liver fibrosis were evaluated.RESULTS:The degree of liver fibrosis was correlated with ICG R15,HH15,LHL15,and HC.HC showed the best correlation with conventional liver function tests.According to multivariate analysis,HC and LHL15 were significant independent predictors of severe fibrosis.HC was the most valuable index for predicting severe fibrosis.CONCLUSION:HC measured with 99mTc-GSA SPECT is a reliable index for assessing liver fibrosis before hepatectomy.
基金Supported by the Practical Research Project for Rare/Intractable Diseases from the Japan Agency for Medical Research and Development(AMED),No.15ek0109053h0002 to Matsumoto Tby grants from the Japan Society for the Promotion of Science(JSPS)KAKENHI,No.25460953,to Umeno J,Esaki M,and Matsumoto T
文摘BACKGROUND We recently reported on a hereditary enteropathy associated with a gene encoding a prostaglandin transporter and referred to as chronic enteropathy associated with SLCO2 A1 gene(CEAS).Crohn's disease(CD)is a major differential diagnosis of CEAS,because these diseases share some clinical features.Therefore,there is a need to develop a convenient screening test to distinguish CEAS from CD.AIM To examine whether prostaglandin E major urinary metabolites(PGE-MUM)can serve as a biomarker to distinguish CEAS from CD.METHODS This was a transactional study of 20 patients with CEAS and 98 patients with CD.CEAS was diagnosed by the confirmation of homozygous or compound heterozygous mutation of SLCO2 A1.We measured the concentration of PGEMUM in spot urine by radioimmunoassay,and the concentration was compared between the two groups of patients.We also determined the optimal cut-off value of PGE-MUM to distinguish CEAS from CD by receiver operating characteristic(ROC)curve analysis.RESULTS Twenty Japanese patients with CEAS and 98 patients with CD were enrolled.PGE-MUM concentration in patients with CEAS was significantly higher than that in patients with CD(median 102.7 vs 27.9μg/g×Cre,P<0.0001).One log unit increase in PGE-MUM contributed to 7.3 increase in the likelihood for the diagnosis of CEAS[95%confidence interval(CI)3.2-16.7].A logistic regression analysis revealed that the association was significant even after adjusting confounding factors(adjusted odds ratio 29.6,95%CI 4.7-185.7).ROC curve analysis revealed the optimal PGE-MUM cut-off value for the distinction of CEAS from CD to be 48.9μg/g×Cre with 95.0%sensitivity and 79.6%specificity.CONCLUSION PGE-MUM measurement is a convenient,non-invasive and useful test for the distinction of CEAS from CD.
