The chiral 2×2 charge order has been reported and confirmed in the kagome superconductor RbV_(3)Sb_(5),while its interplay with superconductivity remains elusive owing to its lowest superconducting transition tem...The chiral 2×2 charge order has been reported and confirmed in the kagome superconductor RbV_(3)Sb_(5),while its interplay with superconductivity remains elusive owing to its lowest superconducting transition temperature Tc of about 0.85K in the AV_(3)Sb_(5) family(A=K,Rb,Cs)that severely challenges electronic spectroscopic probes.Here,utilizing dilution-refrigerator-based scanning tunneling microscopy down to 30 mK,we observe chiral 2×2 pair density waves with residual Fermi arcs in RbV_(3)Sb_(5).We find a superconducting gap of 150 μeV with substantial residual in-gap states.The spatial distribution of this gap exhibits chiral 2×2 modulations,signaling a chiral pair density wave(PDW).Our quasi-particle interference imaging of the zero-energy residual states further reveals arc-like patterns.We discuss the relation of the gap modulations with the residual Fermi arcs under the space-momentum correspondence between PDW and Bogoliubov Fermi states.展开更多
Recent studies have shown that layered compound EuCd_(2)As_(2) could exhibit diverse topological states depending on the different magnetic structures,such as Weyl semimetal,Dirac semimetal and topological insulato r....Recent studies have shown that layered compound EuCd_(2)As_(2) could exhibit diverse topological states depending on the different magnetic structures,such as Weyl semimetal,Dirac semimetal and topological insulato r.In order to further study the interplay between magnetism and topology of EuCd_(2)As_(2),it is necessary to figure out its magnetic structure.Here,by magnetization(M) measurements and negative magnetostriction(λ) along the [001] direction measured by scanning tunneling microscopy on EuCd_(2)As_(2) single crystals,we observe field-induced metamagnetic phase transition from A-type antiferromagnetic(AFM) ground state to field-polarized state,with canted AFM(CAFM) state in between.Magnetization and magnetostriction are more sensitive to the in-plane field than the out-of-plane field,indicating the magnetic moments lying in the ab plane.The absence of abrupt jump on M-H and λ-H curves demonstrates that the phase transition is a second-order type.In CAFM state,M increases linearly with the field and λ is proportional to M~2.Tunneling conductance spectra show the field-induced evolution of the electronic density of states.Our results provide experimental evidence for understanding the magnetic structure of EuCd_(2)As_(2).展开更多
Here we review scanning tunneling microscopy research on the surface determination for various types of kagome materials,including 11-type(CoSn,FeSn,FeGe),32-type(Fe_(3)Sn_(2)),13-type(Mn_(3)Sn),135-type(AV_(3)Sb_(5),...Here we review scanning tunneling microscopy research on the surface determination for various types of kagome materials,including 11-type(CoSn,FeSn,FeGe),32-type(Fe_(3)Sn_(2)),13-type(Mn_(3)Sn),135-type(AV_(3)Sb_(5),A=K,Rb,Cs),166-type(TbMn6Sn_(6),YMn_(6)Sn_(6)and ScV_(6)Sn_(6)),and 322-type(Co_(3)Sn_(2)S_(2)and Ni_(3)In_(2)Se_(2)).We first demonstrate that the measured step height between different surfaces typically deviates from the expected value of±0.4∼0.8Å,which is owing to the tunneling convolution effect with electronic states and becomes a serious issue for Co_(3)Sn_(2)S_(2)where the expected Sn-S interlayer distance is 0.6Å.Hence,we put forward a general methodology for surface determination as atomic step geometry imaging,which is fundamental but also experimentally challenging to locate the step and to image with atomic precision.We discuss how this method can be used to resolve the surface termination puzzle in Co_(3)Sn_(2)S_(2).This method provides a natural explanation for the existence of adatoms and vacancies,and beyond using unknown impurity states,we propose and use designer layer-selective substitutional chemical markers to confirm the validity of this method.Finally,we apply this method to determine the surface of a new kagome material Ni_(3)In_(2)Se_(2),as a cousin of Co_(3)Sn_(2)S_(2),and we image the underlying kagome geometry on the determined Se surface above the kagome layer,which directly visualizes the p-d hybridization physics.We emphasize that this general method does not rely on theory,but the determined surface identity can provide guidelines for first-principles calculations with adjustable parameters on the surface-dependent local density of states and quasi-particle interference patterns.展开更多
基金supported by the National Key R&D Program of China(Grant Nos.2023YFA1407300,2023YFA1406500,2022YFA1403800,and 2023YFF0718403)the National Natural Science Foundation of China(Grant Nos.12374060,12274459,and 12074162)+2 种基金Guangdong Provincial Quantum Science Strategic Initiative(Grant No.GDZX2201001)the Beijing Natural Science Foundation(Grant No.Z200005)Guangdong Basic and Applied Basic Research Foundation(Grant No.2022B1515130005)。
文摘The chiral 2×2 charge order has been reported and confirmed in the kagome superconductor RbV_(3)Sb_(5),while its interplay with superconductivity remains elusive owing to its lowest superconducting transition temperature Tc of about 0.85K in the AV_(3)Sb_(5) family(A=K,Rb,Cs)that severely challenges electronic spectroscopic probes.Here,utilizing dilution-refrigerator-based scanning tunneling microscopy down to 30 mK,we observe chiral 2×2 pair density waves with residual Fermi arcs in RbV_(3)Sb_(5).We find a superconducting gap of 150 μeV with substantial residual in-gap states.The spatial distribution of this gap exhibits chiral 2×2 modulations,signaling a chiral pair density wave(PDW).Our quasi-particle interference imaging of the zero-energy residual states further reveals arc-like patterns.We discuss the relation of the gap modulations with the residual Fermi arcs under the space-momentum correspondence between PDW and Bogoliubov Fermi states.
基金Project supported by the National Natural Science Foundation of China(11227903,12004416,U2032204)the Beijing Municipal Science and Technology Commission(Z181100004218007,Z191100007219011)+3 种基金the National Basic Research Program of China(2015CB921304)the National Key Research and Development Program of China(2017YFA0302903,2016YFJC010282,2016YFA0300602,2016YFA0300604)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB07000000,XDB28000000,XDB33000000)。
文摘Recent studies have shown that layered compound EuCd_(2)As_(2) could exhibit diverse topological states depending on the different magnetic structures,such as Weyl semimetal,Dirac semimetal and topological insulato r.In order to further study the interplay between magnetism and topology of EuCd_(2)As_(2),it is necessary to figure out its magnetic structure.Here,by magnetization(M) measurements and negative magnetostriction(λ) along the [001] direction measured by scanning tunneling microscopy on EuCd_(2)As_(2) single crystals,we observe field-induced metamagnetic phase transition from A-type antiferromagnetic(AFM) ground state to field-polarized state,with canted AFM(CAFM) state in between.Magnetization and magnetostriction are more sensitive to the in-plane field than the out-of-plane field,indicating the magnetic moments lying in the ab plane.The absence of abrupt jump on M-H and λ-H curves demonstrates that the phase transition is a second-order type.In CAFM state,M increases linearly with the field and λ is proportional to M~2.Tunneling conductance spectra show the field-induced evolution of the electronic density of states.Our results provide experimental evidence for understanding the magnetic structure of EuCd_(2)As_(2).
基金support from the National Key R&D Program of China(No.2023YFA1407300)the National Science Foundation of China(No.12374060)+1 种基金Project funded by China Postdoctoral Science Foundation(No.2023M741546,No.2023M731530)The work at Princeton is supported by Gordon and Betty Moore Foundation(GBMF4547 and GBMF9461,M.Z.H.).
文摘Here we review scanning tunneling microscopy research on the surface determination for various types of kagome materials,including 11-type(CoSn,FeSn,FeGe),32-type(Fe_(3)Sn_(2)),13-type(Mn_(3)Sn),135-type(AV_(3)Sb_(5),A=K,Rb,Cs),166-type(TbMn6Sn_(6),YMn_(6)Sn_(6)and ScV_(6)Sn_(6)),and 322-type(Co_(3)Sn_(2)S_(2)and Ni_(3)In_(2)Se_(2)).We first demonstrate that the measured step height between different surfaces typically deviates from the expected value of±0.4∼0.8Å,which is owing to the tunneling convolution effect with electronic states and becomes a serious issue for Co_(3)Sn_(2)S_(2)where the expected Sn-S interlayer distance is 0.6Å.Hence,we put forward a general methodology for surface determination as atomic step geometry imaging,which is fundamental but also experimentally challenging to locate the step and to image with atomic precision.We discuss how this method can be used to resolve the surface termination puzzle in Co_(3)Sn_(2)S_(2).This method provides a natural explanation for the existence of adatoms and vacancies,and beyond using unknown impurity states,we propose and use designer layer-selective substitutional chemical markers to confirm the validity of this method.Finally,we apply this method to determine the surface of a new kagome material Ni_(3)In_(2)Se_(2),as a cousin of Co_(3)Sn_(2)S_(2),and we image the underlying kagome geometry on the determined Se surface above the kagome layer,which directly visualizes the p-d hybridization physics.We emphasize that this general method does not rely on theory,but the determined surface identity can provide guidelines for first-principles calculations with adjustable parameters on the surface-dependent local density of states and quasi-particle interference patterns.
