The interplay between topology and magnetism is vital for realizing exotic quantum phenomena,significant examples including quantum anomalous Hall effect,axion insulators,and high-order topological states.These states...The interplay between topology and magnetism is vital for realizing exotic quantum phenomena,significant examples including quantum anomalous Hall effect,axion insulators,and high-order topological states.These states host great potential for future applications in high-speed and low-consumption electronic devices.Despite being extensively investigated,practical platforms are still scarce.In this work,with molecular beam epitaxy(MBE),we provide the first experimental report on high-quality Bi(110)/CrTe_(2) magnetic heterostructure.By employing in-situ high-resolution scanning tunneling microscopy,we are able to examine the interaction between magnetism and topology.There is a potential edge state at an energy level above the Fermi level,but no edge states observed near the Fermi level The absence of high-order topological corner states near EF highlights the importance of lattice matching and interface engineering in designing high-order topological states.Our study provides key insights into the interplay between two-dimensional magnetic and topological materials and offers an important dimension for engineering magnetic topological states.展开更多
Manipulating emergent quantum phenomena is a key issue for understanding the underlying physics and contributing to possible applications.Here we study the evolution of insulating ground states of Ta_(2)Pu_(3)Te_(5) a...Manipulating emergent quantum phenomena is a key issue for understanding the underlying physics and contributing to possible applications.Here we study the evolution of insulating ground states of Ta_(2)Pu_(3)Te_(5) and Ta_(2)Ni_(3)Te_(5) under in-situ surface potassium deposition via angle-resolved photoemission spectroscopy.Our results confirm the excitonic insulator character of Ta_(2)d_(3)Te_(5).Upon surface doping,the size of its global gap decreases obviously.After a deposition time of more than 7 min,the potassium atoms induce a metal-insulator phase transition and make the system recover to a normal state.In contrast,our results show that the isostructural compound Ta_(2)Ni_(3)Te_(5) is a conventional insulator.The size of its global gap decreases upon surface doping,but persists positive throughout the doping process.Our results not only confirm the excitonic origin of the band gap in Ta_(2)Pd_(3)Te_(5),but also offer an effective method for designing functional quantum devices in the future.展开更多
Searching for the dispersionless flat band(FB)in quantum materials,especially in topological systems,becomes an interesting topic.The kagome lattice is an ideal platform for such exploration because the FB can be natu...Searching for the dispersionless flat band(FB)in quantum materials,especially in topological systems,becomes an interesting topic.The kagome lattice is an ideal platform for such exploration because the FB can be naturally induced by the underlying destructive interference.Nevertheless,the magnetic kagome system that hosts the FB close to the Fermi level(EF)is exceptionally rare.Here,we study the electronic structure of a kagome magnet LuMn6Sn6 by combining angleresolved photoemission spectroscopy and density functional theory calculations.The observed Fermi-surface topology and overall band dispersions are similar to previous studies of the XMn6Sn6(X=Dy,Tb,Gd,Y)family of compounds.We clearly observe two kagome-derived FBs extending through the entire Brillouin zone,and one of them is located just below EF.The photon-energy-dependent measurements reveal that these FBs are nearly dispersionless along the kz direction as well,supporting the quasi-two-dimensional character of such FBs.Our results complement the XMn6Sn6 family and demonstrate the robustness of the FB features across this family.展开更多
One of the greatest triumph of condensed matter physics in the past ten years is the classification of materials by the principle of topology.The existence of topological protected dissipationless surface state makes ...One of the greatest triumph of condensed matter physics in the past ten years is the classification of materials by the principle of topology.The existence of topological protected dissipationless surface state makes topological insulators great potential for applications and hotly studied.However,compared with the prosperity of strong topological insulators,theoretical predicted candidate materials and experimental confirmation of weak topological insulators(WTIs) are both extremely rare.By combining systematic first-principles calculation and angle-resolved photoemission spectroscopy measurements,we have studied the electronic structure of the dark surface of the WTI candidate Zintl Ba_(3)Cd_(2)Sb_(4)and another related material Ba_(3)Cd_(2)As_(4).The existence of two Dirac surface states on specific side surfaces predicted by theoretical calculations and the observed two band inversions in the Brillouin zone give strong evidence to prove that the Ba_(3)Cd_(2)Sb_(4)is a WTI.The spectroscopic characterization of this Zintl Ba_(3)Cd_(2)N_(4)(N = As and Sb) family materials will facilitate applications of their novel topological properties.展开更多
We utilize high-resolution resonant angle-resolved photoemission spectroscopy(ARPES)to study the band structure and hybridization effect of the heavy-fermion compound Ce2 IrIn8.We observe a nearly flat band at the bin...We utilize high-resolution resonant angle-resolved photoemission spectroscopy(ARPES)to study the band structure and hybridization effect of the heavy-fermion compound Ce2 IrIn8.We observe a nearly flat band at the binding energy of 7 meV below the coherent temperature Tcoh^40 K,which characterizes the electrical resistance maximum and indicates the onset temperature of hybridization.However,the Fermi vector and the Fermi surface volume have little change around Tcoh,which challenges the widely believed evolution from a hightemperature small Fermi surface to a low-temperature large Fermi surface.Our experimental results of the band structure fit well with the density functional theory plus dynamic mean-field theory calculations.展开更多
By using angle-resolvea photoemission spectroscopy(ARPES) combined with the first-principies electronic structure calculations,we report the quantized states at the surface of a single crystal 2 H-TaSe_(2).We have obs...By using angle-resolvea photoemission spectroscopy(ARPES) combined with the first-principies electronic structure calculations,we report the quantized states at the surface of a single crystal 2 H-TaSe_(2).We have observed sub-bands of quantized states at the three-dimensional Brillouin zone center due to a highly dispersive band with light effective mass along k_(z) direction.The quantized sub-bands shift upward towards E_(F) while the bulk band at Γ shifts downward with the decrease of temperature across charge density wave(CDW) formation.The band shifts could be intimately related to the CDW.While neither the two-dimensional Fermi-surface nesting nor purely strong electron-phonon coupling can explain the mechanism of CDW in 2 H-TaSe_(2),our experiment may ignite the interest in understanding the CDW mechanism in this family.展开更多
Kagome magnets with diverse topological quantum responses are crucial for next-generation topological engineering.The anisotropic magnetism and band evolution induced by ferromagnetic phase transition(FMPT)is reported...Kagome magnets with diverse topological quantum responses are crucial for next-generation topological engineering.The anisotropic magnetism and band evolution induced by ferromagnetic phase transition(FMPT)is reported in a newly discovered titanium-based kagome ferromagnet Sm Ti3Bi4,which features a distorted Ti kagome lattice and Sm atomic zig-zag chains.Temperature-dependent resistivity,heat capacity,and magnetic susceptibility reveal a ferromagnetic ordering temperature Tc of23.2 K.A large magnetic anisotropy,observed by applying the magnetic field along three crystallographic axes,identifies the b axis as the easy axis.Angle-resolved photoemission spectroscopy with first-principles calculations unveils the characteristic kagome motif,including the Dirac point at the Fermi level and multiple van Hove singularities.Notably,a band splitting and gap closing attributed to FMPT is observed,originating from the exchange coupling between Sm 4 f local moments and itinerant electrons of the kagome Ti atoms,as well as the time-reversal symmetry breaking induced by the long-range ferromagnetic order.Considering the large in-plane magnetization and the evolution of electronic structure under the influence of ferromagnetic ordering,such materials promise to be a new platform for exploring the intricate electronic properties and magnetic phases based on the kagome lattice.展开更多
Kagome lattice,characterized by two-dimensional honeycomb network of corner-sharing triangles[1],presents flat bands,Dirac cones,and van Hove singularities(VHSs),which have been theoretically predicted and experimenta...Kagome lattice,characterized by two-dimensional honeycomb network of corner-sharing triangles[1],presents flat bands,Dirac cones,and van Hove singularities(VHSs),which have been theoretically predicted and experimentally observed[2-4].When combined with spin-orbit coupling(SOC)and magnetism,novel properties have emerged.Although kagome materials vary,most of their strong interlayer interactions make the synthesized crystals not layered,and the properties deviating from the raw two-dimensional kagome lattices.These crystals are difficult to fabricate into thin devices and to tune the physical properties of the materials using gate voltage.展开更多
On-surface Ullmann coupling has been intensely utilized for the tailor-made fabrication of conjugated frameworks towards molecular electronics, however, reaction mechanisms are still limitedly understood. Herein, we p...On-surface Ullmann coupling has been intensely utilized for the tailor-made fabrication of conjugated frameworks towards molecular electronics, however, reaction mechanisms are still limitedly understood. Herein, we provide a comprehensive elucidation of the surface Ullmann coupling of 2,7-dibromopyrene (Br2Py) on Ag(111) by scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and density function theory (DFT), and reveal that the Ullmann reaction path is unique regardless of predesigned assembled structures. By manipulating deposition conditions, diverse assembled architectures have been constructed for Br2Py on Ag(111), including the ladder phase, parallel arrangement, hexagonal patterns from monomers or Kagome lattices based on organometallic (OM) dimers. Intriguingly, stepwise annealing leads to an identical reaction diagram for the surface Ullmann coupling from individual assembled structures convergent into the brick-wall-pattern OM dimers first, which is deemed to be a stable phase, and then into elongated OM chains in order and eventually long-range polymers with direct C-C coupling. While the reaction mechanism is demonstrated to be dominated by the metal coordinated and halogen bonding motifs, interestingly, it has also been revealed that surface adatoms and dissociated Br atoms play a crucial role in coupling reactions. In contrast to previous reports demonstrating the manipulation of Ullmann reactions by preassembled strategy, herein, weak intermolecular interaction in assembled nanostructures is immediately suppressed by strong covalent bonding during reactions. Importantly, our report proposes essential insights on fundamental understanding of surface Ullmann coupling towards high-yield surface synthesis.展开更多
Topological materials and topological phases have recently become a hot topic in condensed matter physics.In this work,we report an In-intercalated transition-metal dichalcogenide In_(x)TaSe_(2)(named 112 system),a to...Topological materials and topological phases have recently become a hot topic in condensed matter physics.In this work,we report an In-intercalated transition-metal dichalcogenide In_(x)TaSe_(2)(named 112 system),a topological nodal-line semimetal in the prep seffiffinffi ce of both charge density wave(CDW)and superconductivity.In the x=0.58 sample,the 2×√3 commensurate CDW(CCDW)and the 2×2 CCDW are observed below 116 and 77 K,respectively.Consistent with theoretical calculations,the spin–orbital coupling gives rise to two twofold-degenerate nodal rings(Weyl rings)connected by drumhead surface states,confirmed by angle-resolved photoemission spectroscopy.Our results suggest that the 2×2 CCDW ordering gaps out one Weyl ring in accordance with the CDW band folding,while the other Weyl ring remains gapless with intact surface states.In addition,superconductivity emerges at 0.91 K,with the upper critical field deviating from the s-wave behavior at low temperature,implying possibly unconventional superconductivity.Therefore,we think this type of the 112 system may possess abundant physical states and offer a platform to investigate the interplay between CDW,nontrivial band topology and superconductivity.展开更多
LaIrIn5 is a reference compound of the heavy-fermion superconductor LaIrIn5.The lack of f electrons in LaIrIn5 indicates that there should not be any f electron participating in the construction of its Fermi surface.T...LaIrIn5 is a reference compound of the heavy-fermion superconductor LaIrIn5.The lack of f electrons in LaIrIn5 indicates that there should not be any f electron participating in the construction of its Fermi surface.Thus the electronic structure comparison between LaIrIn5 and LaIrIn5 provides a good platform to study the properties of f electrons.Here angle-resolved photoemission spectroscopy(ARPES)measurements and density functional theory(DFT)calculations are performed to study the electronic structures of LaIrIn5 and LaIrIn5.We find the valence band structures of the two materials are similar to each other,except for the absence of f bands in LaIrIn5.By analyzing the Fermi crossings of the three conduction bands of the two materials quantitatively,we find the volumes of the electron pocketsαandβaround the M′point become larger from LaIrIn5 to LaIrIn5,while the hole pocketγaround theΓ′point becomes smaller.Together with the calculation results,we confirm that this is mainly originated from the f-electron contribution,while the lattice-constant difference between LaIrIn5 and LaIrIn5 only has a finite influence.We also give a summary of the f-electron character in its related Ce-115 heavy fermion compounds.Our results may be essential for the complete microscopic understanding of the 115 compounds and the related heavy-fermion systems.展开更多
The CoSi family hosts unconventional topological nodes with nonzero Chern numbers.The nontrivial topology is manifested by conspicuous surface Fermi arcs connecting surface projections of the nodes.Here,using angle-re...The CoSi family hosts unconventional topological nodes with nonzero Chern numbers.The nontrivial topology is manifested by conspicuous surface Fermi arcs connecting surface projections of the nodes.Here,using angle-resolved photoemission spectroscopy,we have systematically investigated the(001)surface states of pristine and Ni-doped Co Si.The surface states form saddle-like band structures at/near the time-reversal invariant point near the Fermi level.The Fermi arcs undergo consecutive Lifshitz transitions at the saddle points X,leading to changes of the Fermi arc configuration.As the density of states has a van Hove singularity at the saddle points,exotic many-body physical phenomena may emerge accompanied by the topological transitions of surface Fermi arcs.展开更多
文摘The interplay between topology and magnetism is vital for realizing exotic quantum phenomena,significant examples including quantum anomalous Hall effect,axion insulators,and high-order topological states.These states host great potential for future applications in high-speed and low-consumption electronic devices.Despite being extensively investigated,practical platforms are still scarce.In this work,with molecular beam epitaxy(MBE),we provide the first experimental report on high-quality Bi(110)/CrTe_(2) magnetic heterostructure.By employing in-situ high-resolution scanning tunneling microscopy,we are able to examine the interaction between magnetism and topology.There is a potential edge state at an energy level above the Fermi level,but no edge states observed near the Fermi level The absence of high-order topological corner states near EF highlights the importance of lattice matching and interface engineering in designing high-order topological states.Our study provides key insights into the interplay between two-dimensional magnetic and topological materials and offers an important dimension for engineering magnetic topological states.
基金Project supported by the Ministry of Science and Technology of China (Grant No. 2022YFA1403800)the National Natural Science Foundation of China (Grant Nos. U2032204,12188101, and U22A6005)+2 种基金the Chinese Academy of Sciences (Grant No. XDB33000000)the Synergetic Extreme Condition User Facility (SECUF)the Center for Materials Genome。
文摘Manipulating emergent quantum phenomena is a key issue for understanding the underlying physics and contributing to possible applications.Here we study the evolution of insulating ground states of Ta_(2)Pu_(3)Te_(5) and Ta_(2)Ni_(3)Te_(5) under in-situ surface potassium deposition via angle-resolved photoemission spectroscopy.Our results confirm the excitonic insulator character of Ta_(2)d_(3)Te_(5).Upon surface doping,the size of its global gap decreases obviously.After a deposition time of more than 7 min,the potassium atoms induce a metal-insulator phase transition and make the system recover to a normal state.In contrast,our results show that the isostructural compound Ta_(2)Ni_(3)Te_(5) is a conventional insulator.The size of its global gap decreases upon surface doping,but persists positive throughout the doping process.Our results not only confirm the excitonic origin of the band gap in Ta_(2)Pd_(3)Te_(5),but also offer an effective method for designing functional quantum devices in the future.
基金Project supported by the National Natural Science Foundation of China(Grant No.12204536)the Fundamental Research Funds for the Central Universities,and the Research Funds of People’s Public Security University of China(PPSUC)(Grant No.2023JKF02ZK09).
文摘Searching for the dispersionless flat band(FB)in quantum materials,especially in topological systems,becomes an interesting topic.The kagome lattice is an ideal platform for such exploration because the FB can be naturally induced by the underlying destructive interference.Nevertheless,the magnetic kagome system that hosts the FB close to the Fermi level(EF)is exceptionally rare.Here,we study the electronic structure of a kagome magnet LuMn6Sn6 by combining angleresolved photoemission spectroscopy and density functional theory calculations.The observed Fermi-surface topology and overall band dispersions are similar to previous studies of the XMn6Sn6(X=Dy,Tb,Gd,Y)family of compounds.We clearly observe two kagome-derived FBs extending through the entire Brillouin zone,and one of them is located just below EF.The photon-energy-dependent measurements reveal that these FBs are nearly dispersionless along the kz direction as well,supporting the quasi-two-dimensional character of such FBs.Our results complement the XMn6Sn6 family and demonstrate the robustness of the FB features across this family.
基金supported by the National Key R&D Program of China(Grant Nos.2022YFA1403800,2018YFA0305700,and 2019YFA0308602)the Chinese Academy of Sciences(Grant Nos.QYZDB-SSW-SLH043,XDB33000000,and XDB28000000)+2 种基金the National Natural Science Foundation of China (Grant Nos.U22A600018,U1832202,12074425,11874422,11925408,11921004,and 12188101)the Informatization Plan of Chinese Academy of Sciences (Grant No.CAS-WX2021SF-0102)the Synergetic Extreme Condition User Facility (SECUF)。
文摘One of the greatest triumph of condensed matter physics in the past ten years is the classification of materials by the principle of topology.The existence of topological protected dissipationless surface state makes topological insulators great potential for applications and hotly studied.However,compared with the prosperity of strong topological insulators,theoretical predicted candidate materials and experimental confirmation of weak topological insulators(WTIs) are both extremely rare.By combining systematic first-principles calculation and angle-resolved photoemission spectroscopy measurements,we have studied the electronic structure of the dark surface of the WTI candidate Zintl Ba_(3)Cd_(2)Sb_(4)and another related material Ba_(3)Cd_(2)As_(4).The existence of two Dirac surface states on specific side surfaces predicted by theoretical calculations and the observed two band inversions in the Brillouin zone give strong evidence to prove that the Ba_(3)Cd_(2)Sb_(4)is a WTI.The spectroscopic characterization of this Zintl Ba_(3)Cd_(2)N_(4)(N = As and Sb) family materials will facilitate applications of their novel topological properties.
基金Supported by the National Key Research and Development Program of China under Grant Nos 2016YFA0401000,2015CB921300,2016YFA0300303,2016YFA0401002 and 2017YFA0303103the National Natural Science Foundation of China under Grant Nos 11674371,11774401 and 11874330+4 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences under Grant No XDB07000000the Beijing Municipal Science and Technology Commission under Grant No Z171100002017018the Hundred-Talent Program(type C)of the Chinese Academy of Sciencesthe Sino-Swiss Science and Technology Cooperation under Grant No IZLCZ2-170075the Swiss National Science Foundation under Grant No 200021-159678
文摘We utilize high-resolution resonant angle-resolved photoemission spectroscopy(ARPES)to study the band structure and hybridization effect of the heavy-fermion compound Ce2 IrIn8.We observe a nearly flat band at the binding energy of 7 meV below the coherent temperature Tcoh^40 K,which characterizes the electrical resistance maximum and indicates the onset temperature of hybridization.However,the Fermi vector and the Fermi surface volume have little change around Tcoh,which challenges the widely believed evolution from a hightemperature small Fermi surface to a low-temperature large Fermi surface.Our experimental results of the band structure fit well with the density functional theory plus dynamic mean-field theory calculations.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11774421,11774424,11574394,11774423,11822412,and 11874047)the National Key R&D Program of China(Grant Nos.2016YFA0401002,2018YFA0307000,2016YFA0300504,and 2018FYA0305800)the Fundamental Research Funds for the Central Universities,China(Grant No.2042018kf-0030)。
文摘By using angle-resolvea photoemission spectroscopy(ARPES) combined with the first-principies electronic structure calculations,we report the quantized states at the surface of a single crystal 2 H-TaSe_(2).We have observed sub-bands of quantized states at the three-dimensional Brillouin zone center due to a highly dispersive band with light effective mass along k_(z) direction.The quantized sub-bands shift upward towards E_(F) while the bulk band at Γ shifts downward with the decrease of temperature across charge density wave(CDW) formation.The band shifts could be intimately related to the CDW.While neither the two-dimensional Fermi-surface nesting nor purely strong electron-phonon coupling can explain the mechanism of CDW in 2 H-TaSe_(2),our experiment may ignite the interest in understanding the CDW mechanism in this family.
基金supported by the Synergetic Extreme Condition User Facility(SECUF)the National Key Research and Development Program of China(Grant Nos.2022YFA1403800,2022YFA1403900,and 2018YFE0202600)+3 种基金the National Natural Science Foundation of China(Grant Nos.U22A6005,51832010,11888101,11925408,11921004,and 12188101)the Informatization Plan of the Chinese Academy of Sciences(Grant No.CASWX2021SF-0102)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB33000000,and XDB28000000)the“Dreamline”beamline of Shanghai Synchrotron Radiation Facility(SSRF)。
文摘Kagome magnets with diverse topological quantum responses are crucial for next-generation topological engineering.The anisotropic magnetism and band evolution induced by ferromagnetic phase transition(FMPT)is reported in a newly discovered titanium-based kagome ferromagnet Sm Ti3Bi4,which features a distorted Ti kagome lattice and Sm atomic zig-zag chains.Temperature-dependent resistivity,heat capacity,and magnetic susceptibility reveal a ferromagnetic ordering temperature Tc of23.2 K.A large magnetic anisotropy,observed by applying the magnetic field along three crystallographic axes,identifies the b axis as the easy axis.Angle-resolved photoemission spectroscopy with first-principles calculations unveils the characteristic kagome motif,including the Dirac point at the Fermi level and multiple van Hove singularities.Notably,a band splitting and gap closing attributed to FMPT is observed,originating from the exchange coupling between Sm 4 f local moments and itinerant electrons of the kagome Ti atoms,as well as the time-reversal symmetry breaking induced by the long-range ferromagnetic order.Considering the large in-plane magnetization and the evolution of electronic structure under the influence of ferromagnetic ordering,such materials promise to be a new platform for exploring the intricate electronic properties and magnetic phases based on the kagome lattice.
基金National Key Research and Development Program of China(2022YFA1402404)National Natural Science Foundation of China(92161201,T2221003,12104221,12104220,12274208,12025404,12004174,91961101,61822403,11874203,and 12374043)+1 种基金Natural Science Foundation of Jiangsu Province(BK20230079)Fundamental Research Funds for the Central Universities(020414380192 and 2024300432)。
文摘Kagome lattice,characterized by two-dimensional honeycomb network of corner-sharing triangles[1],presents flat bands,Dirac cones,and van Hove singularities(VHSs),which have been theoretically predicted and experimentally observed[2-4].When combined with spin-orbit coupling(SOC)and magnetism,novel properties have emerged.Although kagome materials vary,most of their strong interlayer interactions make the synthesized crystals not layered,and the properties deviating from the raw two-dimensional kagome lattices.These crystals are difficult to fabricate into thin devices and to tune the physical properties of the materials using gate voltage.
基金supported by the National Natural Science Foundation of China(U1832202,11888101,11920101005,12141402,and 12274459)the Chinese Academy of Sciences(QYZDB-SSW-SLH043,XDB33020100,and XDB28000000)+4 种基金the Beijing Municipal Science and Technology Commission(Z171100002017018,and Z200005)the National Key R&D Program of China(2018YFE0202600,2022YFA1403100,and 2022YFA1403800)the Fundamental Research Funds for the Central Universities and Research Funds of Renmin University of China(RUC)(18XNLG14,19XNLG13,19XNLG17,and 20XNH062)the Synergic Extreme Condition User Facility,Beijing,ChinaBeijing National Laboratory for Condensed Matter Physics。
基金Fruitful discussions with Dr.Qitang Fan are greatly appreciated.This work was financially supported by National Natural Science Foundation of China(Nos.11874380,11874427,and U1732267)the National Key Research and Development Program of China(No.2016YFA040130201)the Hundred Talents Program of Chinese Academy of Sciences.
文摘On-surface Ullmann coupling has been intensely utilized for the tailor-made fabrication of conjugated frameworks towards molecular electronics, however, reaction mechanisms are still limitedly understood. Herein, we provide a comprehensive elucidation of the surface Ullmann coupling of 2,7-dibromopyrene (Br2Py) on Ag(111) by scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and density function theory (DFT), and reveal that the Ullmann reaction path is unique regardless of predesigned assembled structures. By manipulating deposition conditions, diverse assembled architectures have been constructed for Br2Py on Ag(111), including the ladder phase, parallel arrangement, hexagonal patterns from monomers or Kagome lattices based on organometallic (OM) dimers. Intriguingly, stepwise annealing leads to an identical reaction diagram for the surface Ullmann coupling from individual assembled structures convergent into the brick-wall-pattern OM dimers first, which is deemed to be a stable phase, and then into elongated OM chains in order and eventually long-range polymers with direct C-C coupling. While the reaction mechanism is demonstrated to be dominated by the metal coordinated and halogen bonding motifs, interestingly, it has also been revealed that surface adatoms and dissociated Br atoms play a crucial role in coupling reactions. In contrast to previous reports demonstrating the manipulation of Ullmann reactions by preassembled strategy, herein, weak intermolecular interaction in assembled nanostructures is immediately suppressed by strong covalent bonding during reactions. Importantly, our report proposes essential insights on fundamental understanding of surface Ullmann coupling towards high-yield surface synthesis.
基金the National Key R&D Program of the China(2016YFA0300402,2014CB648400,and 2016YFA0300203)the National Natural Science Foundation of China(11774305 and 11274006)the Fundamental Research Funds for the Central Universities of China。
文摘Topological materials and topological phases have recently become a hot topic in condensed matter physics.In this work,we report an In-intercalated transition-metal dichalcogenide In_(x)TaSe_(2)(named 112 system),a topological nodal-line semimetal in the prep seffiffinffi ce of both charge density wave(CDW)and superconductivity.In the x=0.58 sample,the 2×√3 commensurate CDW(CCDW)and the 2×2 CCDW are observed below 116 and 77 K,respectively.Consistent with theoretical calculations,the spin–orbital coupling gives rise to two twofold-degenerate nodal rings(Weyl rings)connected by drumhead surface states,confirmed by angle-resolved photoemission spectroscopy.Our results suggest that the 2×2 CCDW ordering gaps out one Weyl ring in accordance with the CDW band folding,while the other Weyl ring remains gapless with intact surface states.In addition,superconductivity emerges at 0.91 K,with the upper critical field deviating from the s-wave behavior at low temperature,implying possibly unconventional superconductivity.Therefore,we think this type of the 112 system may possess abundant physical states and offer a platform to investigate the interplay between CDW,nontrivial band topology and superconductivity.
基金supported by the National Natural Science Foundation of China(Grant Nos.11874330,11774320,U1630248,and 11904334)the National Key Research and Development Program of China(Grant No.2017YFA0303104)+5 种基金the National Key R&D Program of the MOST of China(Grant No.2016YFA0300204)the special fund from Institute of Materials,CAEP(Grant No.TP02201904)the Equipment development fund(Grant No.JZX7Y201901SY00900107)the Science Challenge Project(Grant No.TZ2016004)Part of this research used Beamline 03U of the Shanghai Synchron Radiation Facility,which is supported by ME2 project under contract No.11227902 from National Natural Science Foundation of Chinasupported by“Award for Outstanding Member in Youth Innovation Promotion Association CAS”。
文摘LaIrIn5 is a reference compound of the heavy-fermion superconductor LaIrIn5.The lack of f electrons in LaIrIn5 indicates that there should not be any f electron participating in the construction of its Fermi surface.Thus the electronic structure comparison between LaIrIn5 and LaIrIn5 provides a good platform to study the properties of f electrons.Here angle-resolved photoemission spectroscopy(ARPES)measurements and density functional theory(DFT)calculations are performed to study the electronic structures of LaIrIn5 and LaIrIn5.We find the valence band structures of the two materials are similar to each other,except for the absence of f bands in LaIrIn5.By analyzing the Fermi crossings of the three conduction bands of the two materials quantitatively,we find the volumes of the electron pocketsαandβaround the M′point become larger from LaIrIn5 to LaIrIn5,while the hole pocketγaround theΓ′point becomes smaller.Together with the calculation results,we confirm that this is mainly originated from the f-electron contribution,while the lattice-constant difference between LaIrIn5 and LaIrIn5 only has a finite influence.We also give a summary of the f-electron character in its related Ce-115 heavy fermion compounds.Our results may be essential for the complete microscopic understanding of the 115 compounds and the related heavy-fermion systems.
基金supported by the Ministry of Science and Technology of China(Grant Nos.2016YFA0401000,2016YFA0300600,2018YFE0202600,and 2016YFA0300504)the National Natural Science Foundation of China(Grant Nos.U1832202,11774423,118224121,and 1888101)+4 种基金the Chinese Academy of Sciences(Grant Nos.QYZDB-SSW-SLH043,XDB33020100,and XDB28000000)the Beijing Natural Science Foundation(Grant No.Z200005)the Fundamental Research Funds for the Central Universities and Research Funds of Renmin University of China(Grant Nos.18XNLG14,and 19XNLG17)the Beijing Municipal Science and Technology Commission(Grant No.Z171100002017018)support by the CAS Pioneer“Hundred Talents Program”(type C)。
文摘The CoSi family hosts unconventional topological nodes with nonzero Chern numbers.The nontrivial topology is manifested by conspicuous surface Fermi arcs connecting surface projections of the nodes.Here,using angle-resolved photoemission spectroscopy,we have systematically investigated the(001)surface states of pristine and Ni-doped Co Si.The surface states form saddle-like band structures at/near the time-reversal invariant point near the Fermi level.The Fermi arcs undergo consecutive Lifshitz transitions at the saddle points X,leading to changes of the Fermi arc configuration.As the density of states has a van Hove singularity at the saddle points,exotic many-body physical phenomena may emerge accompanied by the topological transitions of surface Fermi arcs.
