Twisted bilayer graphene(TBG) has been extensively studied because of its novel physical properties and potential application in electronic devices.Here we report the synthesis and characterization of 300 TBG naturall...Twisted bilayer graphene(TBG) has been extensively studied because of its novel physical properties and potential application in electronic devices.Here we report the synthesis and characterization of 300 TBG naturally grown on Cu_(0.75)Ni_(0.25)(111) film and investigate the electronic structure by angle-resolved photoemission spectroscopy.Compared with other substrates,our TBG with a wafer scale is acquired with a shorter growth time.The Fermi velocity and energy gap of Dirac cones of TBG are comparable with those of a monolayer on Cu_(0.85)Ni_(0.15)(111).The signature of moré lattices has not been observed in either the low-energy electron diffraction patterns or the Fermi surface map within experimental resolution,possibly due to different Cu and Ni contents in the substrates enhancing the different couplings between the substrate and the first/second layers and hindering the formation of a quasiperiodic structure.展开更多
The iron-based superconductivity (IBSC) is a great challenge in correlated system. Angle-resolved photoemission spectroscopy (ARPES) provides electronic structure of the IBSCs, the pairing strength, and the order ...The iron-based superconductivity (IBSC) is a great challenge in correlated system. Angle-resolved photoemission spectroscopy (ARPES) provides electronic structure of the IBSCs, the pairing strength, and the order parameter symmetry. Here, we briefly review the recent progress in IBSCs and focus on the results from ARPES. The ARPES study shows the electronic structure of "122", "111", "11", and "122"" families of IBSCs. It has been agreed that the IBSCs are unconventional superconductors in strong coupling region. The order parameter symmetry basically follows s form with considerable out-of-plane contribution.展开更多
Graphene with a Dirac cone-like electronic structure has been extensively studied because of its novel transport properties and potential application for future electronic devices.For epitaxially grown graphene,the pr...Graphene with a Dirac cone-like electronic structure has been extensively studied because of its novel transport properties and potential application for future electronic devices.For epitaxially grown graphene,the process conditions and the microstructures are strongly dependent on various substrate materials with different lattice constants and interface energies.Utilizing angle-resolved photoemission spectroscopy,here we report an investigation of the electronic structure of single-crystalline graphene grown on Cu/Ni(111)alloy film by chemical vapor deposition.With a relatively low growth temperature,graphene on Cu/Ni(111)exhibits a Dirac cone-like dispersion comparable to that of graphene grown on Cu(111).The linear dispersions forming Dirac cone are as wide as 2 e V,with the Fermi velocity of approximately 1.1×10^6 m/s.Dirac cone opens a gap of approximately 152 meV at the binding energy of approximately 304 meV.Our findings would promote the study of engineering of graphene on different substrate materials.展开更多
Recently, 5d transition metal iridates have been reported as promising materials for the manttfacture of exotic quan- tum states. Apart from the semimetallic ground states that have been observed, perovskite SrlrO3 is...Recently, 5d transition metal iridates have been reported as promising materials for the manttfacture of exotic quan- tum states. Apart from the semimetallic ground states that have been observed, perovskite SrlrO3 is also predicted to have a lattice-symmetrically protected topological state in the (110) plane due to its strong: spin-orbil coupling and electron correlation. Compared with non-polar (001)-SflrO3, the especial polarity of (110)-SrIrC)3 undoubtedly adds the: difficulty of fabrication and largely impedes the research on its surface states. Here, we have successfully synthesized high-quality (110)-SflrO3 thin films on (110)-SrTiO3 substrates by reactive molecular beam epitaxy fi^r the first time. Both reflec- tion high-energy electron diffraction pattems and x-ray diffraction measurements suggest the expected orientation and outstanding crystallinity. A (1 × 2) surface reconstruction driven from the surface instabiJity, the. same as that reported in (110)-SrTiO3, is observed. The electric transport measurements uncover that (110)-SrIrO3 exhibits a more prominent semimetallic property in comparison to (001)-SrIrO3.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
Signatures of topological superconductivity(TSC)in superconducting materials with topological nontrivial states prompt intensive researches recently.Utilizing high-resolution angle-resolved photoemission spectroscopy ...Signatures of topological superconductivity(TSC)in superconducting materials with topological nontrivial states prompt intensive researches recently.Utilizing high-resolution angle-resolved photoemission spectroscopy and first-principles calculations,we demonstrate multiple Dirac fermions and surface states in superconductor BaSn_(3) with a critical transition temperature of about 4.4 K.We predict and then unveil the existence of two pairs of type-Ⅰtopological Dirac fermions residing on the rotational axis.Type-ⅡDirac fermions protected by screw axis are confirmed in the same compound.Further calculation for the spin helical texture of the observed surface states originating from the Dirac fermions gives an opportunity for realization of TSC in one single material.Hosting multiple Dirac fermions and topological surface states,the intrinsic superconductor BaSn_(3) is expected to be a new platform for further investigation of topological quantum materials as well as TSC.展开更多
Using angle-resolved photoemission spectroscopy, we study the low-energy electronic structure of a layered ternary telluride EuSbTe3 semiconductor. It is found that the photoemission constant energy contours can be we...Using angle-resolved photoemission spectroscopy, we study the low-energy electronic structure of a layered ternary telluride EuSbTe3 semiconductor. It is found that the photoemission constant energy contours can be well described by the simple two-parameter(t(perp) and t(para)) tight-binding model based on the Te orbitals in square-net planes of EuSbTe3, suggesting its Te 5p orbitals dominated low-lying electronic structure, which is reminiscent of other rare-earth tritellurides. However, a possible charge-density-wave gap of 80 meV is found to persist in 300 K,which renders the unexpected semiconducting properties in EuSbTe3. Moreover, we reveal an extra band gap occurring around 200 meV below the Fermi level at low temperatures, which can be attributed to the interaction between the main and folded bands due to lattice scatterings. Our findings provide the first comprehensive understanding of the electronic structure of layered ternary tellurides, which lays the basis for future research on these compounds.展开更多
基金Project supported by the National Key R&D Program of China (Grant Nos. 2022YFB3608000 and 2022YFA1204900)the National Natural Science Foundation of China (Grant Nos. 12222413 and 12074205)+2 种基金the Natural Science Foundation of Shanghai (Grant Nos. 23ZR1482200 and 22ZR1473300)the Natural Science Foundation of Zhejiang Province (Grant No. LQ21A040004)the funding of Ningbo University (Grant No. LJ2024003)。
文摘Twisted bilayer graphene(TBG) has been extensively studied because of its novel physical properties and potential application in electronic devices.Here we report the synthesis and characterization of 300 TBG naturally grown on Cu_(0.75)Ni_(0.25)(111) film and investigate the electronic structure by angle-resolved photoemission spectroscopy.Compared with other substrates,our TBG with a wafer scale is acquired with a shorter growth time.The Fermi velocity and energy gap of Dirac cones of TBG are comparable with those of a monolayer on Cu_(0.85)Ni_(0.15)(111).The signature of moré lattices has not been observed in either the low-energy electron diffraction patterns or the Fermi surface map within experimental resolution,possibly due to different Cu and Ni contents in the substrates enhancing the different couplings between the substrate and the first/second layers and hindering the formation of a quasiperiodic structure.
基金supported by the National Natural Science Foundation of China(Grant No.11274381)the National Basic Research Program of China(GrantNo.2010CB923000)
文摘The iron-based superconductivity (IBSC) is a great challenge in correlated system. Angle-resolved photoemission spectroscopy (ARPES) provides electronic structure of the IBSCs, the pairing strength, and the order parameter symmetry. Here, we briefly review the recent progress in IBSCs and focus on the results from ARPES. The ARPES study shows the electronic structure of "122", "111", "11", and "122"" families of IBSCs. It has been agreed that the IBSCs are unconventional superconductors in strong coupling region. The order parameter symmetry basically follows s form with considerable out-of-plane contribution.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51772317,11604356,and 11704394)
文摘Graphene with a Dirac cone-like electronic structure has been extensively studied because of its novel transport properties and potential application for future electronic devices.For epitaxially grown graphene,the process conditions and the microstructures are strongly dependent on various substrate materials with different lattice constants and interface energies.Utilizing angle-resolved photoemission spectroscopy,here we report an investigation of the electronic structure of single-crystalline graphene grown on Cu/Ni(111)alloy film by chemical vapor deposition.With a relatively low growth temperature,graphene on Cu/Ni(111)exhibits a Dirac cone-like dispersion comparable to that of graphene grown on Cu(111).The linear dispersions forming Dirac cone are as wide as 2 e V,with the Fermi velocity of approximately 1.1×10^6 m/s.Dirac cone opens a gap of approximately 152 meV at the binding energy of approximately 304 meV.Our findings would promote the study of engineering of graphene on different substrate materials.
基金Project supported by the National Key Research and Development Program of the MOST of China(Grant No.2016YFA0300204)the National Key Basic Research Program of China(Grant No.2015CB654901)+2 种基金the National Natural Science Foundation of China(Grant Nos.11574337,11227902,11474147,and11704394)Shanghai Sailing Program(Grant No.17YF1422900)the Award for Outstanding Member in Youth Innovation Promotion Association of the Chinese Academy of Sciences
文摘Recently, 5d transition metal iridates have been reported as promising materials for the manttfacture of exotic quan- tum states. Apart from the semimetallic ground states that have been observed, perovskite SrlrO3 is also predicted to have a lattice-symmetrically protected topological state in the (110) plane due to its strong: spin-orbil coupling and electron correlation. Compared with non-polar (001)-SflrO3, the especial polarity of (110)-SrIrC)3 undoubtedly adds the: difficulty of fabrication and largely impedes the research on its surface states. Here, we have successfully synthesized high-quality (110)-SflrO3 thin films on (110)-SrTiO3 substrates by reactive molecular beam epitaxy fi^r the first time. Both reflec- tion high-energy electron diffraction pattems and x-ray diffraction measurements suggest the expected orientation and outstanding crystallinity. A (1 × 2) surface reconstruction driven from the surface instabiJity, the. same as that reported in (110)-SrTiO3, is observed. The electric transport measurements uncover that (110)-SrIrO3 exhibits a more prominent semimetallic property in comparison to (001)-SrIrO3.
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 National Key R&D Program of China (Grant No. 2016YFA0300204)the National Natural Science Foundation of China (Grant Nos. U2032208 and 11874264)+6 种基金the Natural Science Foundation of Shanghai (Grant No. 14ZR1447600)the starting grant of Shanghai Tech University and the Program for Professor of Special Appointment (Shanghai Eastern Scholar)supported by ME~2 project (Grant No. 11227902) from the National Natural Science Foundation of Chinasupported by the National Natural Science Foundation of China (Grant No. 11974395)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB33000000)the Center for Materials Genomethe support from Analytical Instrumentation Center,SPST,Shanghai Tech University (Grant No. SPST-AIC10112914)
文摘Signatures of topological superconductivity(TSC)in superconducting materials with topological nontrivial states prompt intensive researches recently.Utilizing high-resolution angle-resolved photoemission spectroscopy and first-principles calculations,we demonstrate multiple Dirac fermions and surface states in superconductor BaSn_(3) with a critical transition temperature of about 4.4 K.We predict and then unveil the existence of two pairs of type-Ⅰtopological Dirac fermions residing on the rotational axis.Type-ⅡDirac fermions protected by screw axis are confirmed in the same compound.Further calculation for the spin helical texture of the observed surface states originating from the Dirac fermions gives an opportunity for realization of TSC in one single material.Hosting multiple Dirac fermions and topological surface states,the intrinsic superconductor BaSn_(3) is expected to be a new platform for further investigation of topological quantum materials as well as TSC.
基金Supported by the National Key R&D Program of China under Grant No 2016YFA0300204the National Basic Research Program of China under Grant No 2015CB654901+2 种基金the National Natural Science Foundation of China under Grant Nos 11574337,11227902,11474147 and 11704394the Shanghai Sailing Program under Grant No 17YF1422900the Award for Outstanding Member in Youth Innovation Promotion Association CAS
文摘Using angle-resolved photoemission spectroscopy, we study the low-energy electronic structure of a layered ternary telluride EuSbTe3 semiconductor. It is found that the photoemission constant energy contours can be well described by the simple two-parameter(t(perp) and t(para)) tight-binding model based on the Te orbitals in square-net planes of EuSbTe3, suggesting its Te 5p orbitals dominated low-lying electronic structure, which is reminiscent of other rare-earth tritellurides. However, a possible charge-density-wave gap of 80 meV is found to persist in 300 K,which renders the unexpected semiconducting properties in EuSbTe3. Moreover, we reveal an extra band gap occurring around 200 meV below the Fermi level at low temperatures, which can be attributed to the interaction between the main and folded bands due to lattice scatterings. Our findings provide the first comprehensive understanding of the electronic structure of layered ternary tellurides, which lays the basis for future research on these compounds.
基金This work was supported by the National Key R&D Program of the MOST of China(2016YFA0300204)the National Natural Science Foundation of China(11574337,11874199,and 11874263)+2 种基金supported by the National Basic Research Program of China(2015CB654901)Part of this research used Beamline 03U of the Shanghai Synchron Radiation Facility,which is supported by ME2 project(11227902)from the National Natural Science Foundation of Chinasupported by‘‘Award for Outstanding Member in Youth Innovation Promotion Association CAS”。