Theoretical Study On Manipulation Of Band Structure And Local Magnetic Moment Of 2D Electronic Systems By Adatoms

Since the 1980 s,with the rapid development of scanning tunneling microscopy(STM)and other surface technologies,it has become increasingly common to design and control the adsorbed atoms on surfaces to regulate the physical properties of two-dimensional(2D)electronic systems.The famous quantum corral experiment is a typical example of using surface adsorbed atoms to regulate the two-dimensional electronic states on a metal surface.In the quantum corral experiment,adatoms on metal surface are arranged into an atomic fence by atomic manipulation with STM tip.As a 2D electronic system,the electronic wave function of metal surface state is modulated by the scattering of the atomic fence and clearly shows the wave characteristics.Then by controlling and designing the shape of the quantum corral,people can create desired corral bound states.In recent 20 years,with the rapid development of two-dimensional materials such as graphene,controlling the energy bands,spin and topological properties of various 2D systems by purposefully adsorbing different atoms on the 2D surfaces has been widely studied.How to modulate the physical properties of 2D electronic systems by adsorbed atoms is still a hot topic in condensed matter physics.In this thesis,combining with the recent important advances in surface atom adsorption experiments,we theoretically and systematically study two specific applications of regulating the physical properties of 2D systems through adsorbing atoms on its surfaces:(1)Based on the theoretical calculation and simulation,we first propose an experimental scheme for the preparation of artificial electronic Kagome lattice on Cu(111)surface by designing an appropriate arrangement of the adsorbed CO molecules,and then we design the artificial electronic Lieb lattice using this method.In 2012,K.K.Gomes,et al.,first fabricated a novel two-dimensional artificial electronic lattice on the metal surface [Cu(111)]: molecular graphene [K.K.Gomes et al.,Nature(London)483,306(2012)].In the experiment,the CO molecules adsorbed on Cu(111)surface are arranged into a regular triangular lattice by atomic manipulation with STM.The electrons on Cu(111)surface are scattered by the periodic molecular potential to form a honeycomb electron lattice and transform into the Dirac fermions with linear dispersion.In our work,we theoretically propose that with this technique,we can build other complex artificial electronic lattices with peculiar energy bands,such as Kagome and Lieb lattices.This metal surface system is a quantum anti-dot system due to the repulsive potential exerted by the adsorbed CO molecules.Utilizing this property,we design the arrangement of the adsorbed CO molecules on Cu(111)surface for constructing the Kagome and Lieb electron lattices,and adopt an effective theoretical model to simulate and numerically prove the correctness and feasibility of our design.This kind of artificial two-dimensional electronic lattice on metal surface is expected to serve as a new quantum simulation platform to investigate the basic physical properties and many-body effects of 2D electronic systems.Meanwhile,our proposed experimental scheme of the electronic Lieb lattice on metal surface has already been verified in experiments [M.R.Slot et al.,Nature Physics 13,672-676(2017)];(2)We propose a simple and equivalent Anderson impurity model to describe the local magnetic moment oscillation in graphene induced by hydrogen atom adsorption.The hydrogen-adsorption-induced local magnetic moment in graphene has always been a hot topic in the studies of graphene spintronics.This phenomenon was predicted theoretically in 2007(by first-principles calculations),and it was not observed experimentally until 2016 [Gonz'alez-Herrero et al.,Science 352,437(2016)].In the experiment,the longrange(about 2 nm)local magnetic moment oscillation was observed at the carbon atoms of graphene near the adsorbed hydrogen atom by STM measurement.Theoretically,it is generally believed that the local magnetic moment is caused by the Coulomb interaction of electrons on the carbon atoms of graphene.But if the Coulomb interaction of graphene electrons is taken into account,from the perspective of theoretical calculations,we must build a supercell of graphene with an enormous number of atoms.Thus we can only describe the local magnetic moment oscillation phenomenon by complex numerical simulations(for example,first-principles simulations).Here,we propose through theoretical analysis that the effect of Coulomb interaction of graphene electrons can be described by a simple Anderson impurity model,and all the effects of the Coulomb interaction can be equivalent to a fitting parameter: the on-site Coulomb interaction U at the impurity.This model overcomes the difficulty of describing the magnetic moment oscillation only by complex numerical simulations for a long time,greatly simplifies the calculations and perfectly explains all the experimental phenomena reported by Science(including the cases of a single hydrogen atom and hydrogen dimer).Our model provides a concise physical picture for understanding the important phenomenon of hydrogen-induced magnetic moment oscillation in graphene;(3)Based on our theoretical model,we further point out that the magnetic moment oscillation in graphene induced by hydrogen adsorption can be equivalent to a Friedel oscillation in magnetic moment,and an analytical expression of the magnetic moment oscillation is derived.Our calculations show that although the experimentallyobserved magnetic moment induced by hydrogen adsorption monotonically decays with the distance from the impurity,if appropriate doping is adopted(through gate voltage),it will form Friedel oscillations as a Sine function,and the magnetic moment oscillations on the two sublattices of graphene can have different oscillation phases.We expect that such Friedel oscillations in magnetic moment can be observed by spin polarized STM.