| Low-dimensional quantum materials have attracted wide interest due to their novel physical properties and potential application prospects.Molecular beam epitaxy(MBE)and scanning tunneling microscope(STM)are powerful methods for preparing and studying low-dimensional quantum materials.To this end,we independently designed and built two sets of molecular beam epitaxy systems,including vacuum chambers,a pump set,a sample console,a sample growth monitoring device,an argon ion sputtering gun,and a needle tip processing device.We also integrated two sets of molecular beam epitaxy systems that we built independently into two sets of commercial scanning tunneling microscope systems of low temperature(5 K)and room temperature produced by Unisoku.Both sets of MBE-STM joint systems can be used for the growth of low-dimensional quantum material systems and the characterization of atomic-level morphology and electronic structure,which effectively improve our research efficiency and ability.In addition,under the synergy of the spin-orbit coupling effect,a topological superconducting state can be realized in the heterostructures combining 2D ferromagnetism with superconductivity in theory,which is characterized by the induction of the Majorana edge state in the superconducting energy gap on the boundary of the ferromagnetic island.At present,it is theoretically predicted that monolayer VSe2 has intrinsic ferromagnetism,but the research results of various experimental methods are inconsistent,and the magnetic properties of monolayer VSe2 have yet to be confirmed.In this thesis,we use the MBE method to grow monolayer VSe2 on s-wave superconductor NbSe2 substrate to construct a two-dimensional transition metal dichalcogenides(2D-TMDs)heterostructure.And we use the scanning tunneling microscope/spectroscopy(STM/STS)surface analysis techniques to study the structure and electronic properties of the heterostructure,to further confirm the magnetic properties of monolayer VSe2 and to find possible Majorana boundary state.In our study,we discovered three phases of monolayer VSe2:the reported31/2×71/2 and 2×31/2 chare density wave(CDW)phase,the disordered phase,the never reported31/2×31/2CDW phase.The structure and electronic properties of31/2×71/2 and 2×31/2 CDW phase are consistent with the report,and it is not magnetic.The disordered phase maintains the original lattice structure,but the surface electronic states are not uniform.The superconductivity in the VSe2 islands are suppressed,the superconducting energy gap and coherent peaks almost disappear,which may be ferromagnetic,but no topological superconducting signal is found at the boundary.The31/2×31/2 superlattice of31/2×31/2CDW phase and the31/2 times lattice of NbSe2 are common,and the surface selenium atoms dimerize.31/2×31/2 CDW phase is not ferromagnetic,but a sharp peak appears near the Fermi level.We further found that the influence of the boundary and defects on the sharp peak is similar to the change trend of the carrier doping in the center of the twisted bilayer graphene AA stack area,so it is speculated that this structure may form a narrow band near the Fermi surface,resulting in the appearance of the sharp peak.The narrow band near the Fermi surface may have new electronic correlation properties through regulation.If the speculation is confirmed,this system can provide a new research platform for the related physics research of the 2D-TMDs heterostructures. |
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