Wafer-scale 30°twisted bilayer graphene epitaxially grown on Cu_(0.75)Ni_(0.25)(111)

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.

High-resolution ARPES endstation for in situ electronic structure investigations at SSRF

Angle-resolved photoemission spectroscopy(ARPES)is one of the most powerful experimental techniques in condensed matter physics.Synchrotron ARPES,which uses photons with high flux and continuously tunable energy,has become particularly important.However,an excellent synchrotron ARPES system must have features such as a small beam spot,super-high energy resolution,and a user-friendly operation interface.A synchrotron beamline and an endstation(BL03 U)were designed and constructed at the Shanghai Synchrotron Radiation Facility.The beam spot size at the sample position is 7.5(V)μm×67(H)μm,and the fundamental photon range is 7-165 eV;the ARPES system enables photoemission with an energy resolution of 2.67 meV at21.2 eV.In addition,the ARPES system of this endstation is equipped with a six-axis cryogenic sample manipulator(the lowest temperature is 7 K)and is integrated with an oxide molecular beam epitaxy system and a scanning tunneling microscope,which can provide an advanced platform for in situ characterization of the fine electronic structure of condensed matter.

Electronic structure of single-crystalline graphene grown on Cu/Ni(111) alloy film

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.

Investigation of the room-temperature photoelectron spectroscopy of type-Ⅱ Weyl semimetal candidate WTe_(2)

Layered transition metal dichalcogenides have novel physical properties and great potential for applications.Among them,WTe2,which has an extremely large unsaturated magnetoresistance and is theoretically predicted to be a type-Ⅱ Weyl semimetal,has been extensively studied.Here,we systematically probe the electronic structure of WTe_(2) at room temperature using high-resolution angle-resolved photoelectron spectroscopy(ARPES).We find that temperature-driven chemical potential shift and Lifshitz transition,which is equivalent to low-energy band structures shift downward by around 50 meV,compared to the results at low temperatures.Our ARPES experimental results match well with previous theoretical calculations,implying the possible existence of type-Ⅱ Weyl points near the Γ-X axis.Also,as expected,there exists a dominantly electron-like Fermi surface instead of the one with compensated electrons and holes.Meanwhile,our ARPES results show that the flat band(FB) lying below the Fermi level(EF) becomes closer to the Fermi level at room temperature,which might start to dominate the transport behavior and lead to the disappearance of the unsaturated giant magnetoresistance effect.These findings not only reveal the electronic structure features of WTe_(2) at room temperature,but also provide new insights into the development of room-temperature topological quantum devices.