Angle-resolved Photoemission Spectroscopy Studies Of 2D Material Heterostructures

Two-dimensional(2D)materials provide the various and important platforms for realizing new quantum phenomena,exploring new physics and designing new quantum devices.By stacking different 2D materials together,and utilizing the interfacial periodical potential and order-parameter coupling,the electronic structures of the heterostructure can be tuned to achieve novel properties distinct from the constitute materials.This thesis focuses on three typical 2D material heterostructures(graphene/h-BN,twisted bilayer graphene and topological insulator/high-temperature superconductor).1.We investigated the van der Waals heterostructure-graphene/h-BN utilizing angleresolved photoemission spectroscopy(ARPES)and for the first time obtained its modulated band structure.The results directly show the spectrum of secondgeneration Dirac cones,originated from the moiré potential caused by lattice mismatch.Meanwhile,we observe gap ? 100 me V and ? 160 me V at the secondgeneration and original Dirac cones.This work highlights the important role of inversion symmetry breaking on band structure modulation in heterostructures and provides the experimental baseline for understanding the physics in this prototypical heterostructure.2.Twisted bilayer graphene(t BLG)can be viewed as a simpler van der Waals heterostructure,yet with no lattice mismatch.For the first time,we utilized nanospot angle-resolved photoemission spectroscopy(nano-ARPES)to study the band structure of 6?t BLG with sample size around only a few micrometers.We directly resolved that the hybridization between the original and replica cones leads to the formation of second-generation Dirac cone below the van Hove singularity.This reveals the electronic origin of the recently observed Hofstadter butterfly states in t BLG and demonstrate the possibility of band modulation by simply twisting the stacked 2D materials.3.We demonstrate the first study on the band structure of topological insulator/hightemperature superconductor heterostructure-Bi2Se3/Bi2Sr2 Ca Cu2O8+?.Utilizing ARPES,we directly resolved the gap opening ? 15 me V at the surface states of Bi2Se3,due to the interfacial proximity effect.This provides a new platform for realizing Majorana Fermion in condensed matter physics,which has great application potential for topological quantum computation.These studies show the rich physics in 2D material heterostructures and prove the2 D material heterostructure has become an important research ares with great potential.More possibilities and new functionalities are waiting for investigation in the future.