Investigation Of Magnetic Topological States And Mott Insulators

Topological quantum states and strongly correlated systems represent two important fields within condensed matter physics,both of which have significantly advanced modern physics.In recent decades,tremendous success has been achieved in the theoretical and experimental explorations of nonmagnetic topological states.However,the intricate interactions introduced by magnetic orders have posed challenges for theoretical analysis and experimental verification.Following scientist’s pursuit of the quantum anomalous Hall effect（QAHE）,the author reviews the development of magnetic topological states in Chapter 1.Using the angle-resolved photoemission spectroscopy（ARPES）,as introduced in Chapter 3,the author carried out detailed studies of these magnetic topological materials,yielding two important findings:（1）In Chapter 4,the author performed detailed ARPES studies on the electronic structures of the intrinsic antiferromagnetic topological insulators Mn Bi_2nTe_3n+1 family.The author observed nearly gapless Dirac surface states,and further discussed the effect of the magnetic order on the Dirac surface states.Furthermore,the author observed three type Dirac surface states with different termination on the（001）surface of the Mn B₆Te₁₀ single crystal.In addition,the author investigated the feasibility of realizing high-temperature QAHE in few-layer Mn Bi₆Te₁₀.（2）In Chapter 5,the author discovered the termination-dependent dispersions of EuB₆,and visualized the topological phase transition of bulk bands driven by time reversal symmetry breaking,confirming that EuB₆ is a magnetic topological semimetal.Remarkably,the author found that the magnetic topological state has an ideal electronic structures,and the crossing points are located at the Fermi level without interference from other trivial bands.This discovery provides an excellent platform for exploring novel quantum phenomena in magnetic topological materials,such as the high temperature QAHE at the 2D limit.The vigorous development of topological quantum states proves the success of the band theory.Nevertheless,numerous exotic phenomena in strongly correlated systems remain beyond the grasp of band theory based on single-particle approximation,such as the Mott insulator.While numerous Mott insulators have been experimentally identified,the low-energy excitations of most systems are highly complex,with only a few qualifying as the single-band Mott–Hubbard insulator.Consequently,an ideal single-band Mott-Hubbard insulator could serve as an excellent starting point for exploring many correlation phenomena.The author reviews the intricate interactions in Mott insulators in Chapter 2,and highlights the significance of studying single-band Mott insulators.The author describes the Mott physics in the Nb₃Cl₈ system in Chapter（3）In Chapter 6,by combining the dynamical mean-field theory,angle-resolved photoemission spectroscopy,and photoluminescence spectroscopy,the author dentified a model single-band Mott-Hubbard insulator state in a-Nb₃Cl₈ unambiguously,providing a paradigm for studying Mott physics.Furthermore,the author performed temperature-dependent measurements of the electronic structures of b-Nb₃Cl₂Br_6,finding a bonding/antibonding splitting caused by enhanced interlayer coupling.Nevertheless,the energy gap remains dominated by the electron correlation,so the b phase is still a Mott insulator.In the exploration of magnetic topology states or Mott insulators,physicists have consistently sought ideal system with the simplest degree of freedom.It is anticipated that in the near future,exotic topological states and correlation physics will be realized and controlled based on these ideal materials.