Theoretical Study On The Correlation Effect Of Antiferromagnetic State FeSe

In recent years,iron-based superconductors have attracted extensive attention.Condensed matter physicists are hope to break through the belief that high-temperature superconductors cannot contain magnetic atoms by studying such new high-temperature superconducting materials containing magnetic ions.When the temperature of bulk FeSe material drops to about 90K,there is a structural transition from tetragonal to orthogonal phase,which companied by a new structural phase---nematic phase.However,despite the large amount of results,the origin of nematic phase is not still determined.The main viewpoints on nematic phase are believe that nematic structure is derived from the magnetic order and the orbital order.FeSe is a correlated electronic system material,and the correlation effect has a great influence on its electronic properties.Exploring its influence on superconductivity is also a hot topic and difficult problem in the field of condensed matter physics.In this paper,the electronic properties of antiferromagnetic monolayer FeSe are studied by first-principles method,and Hubbard's corrected density functional theory?LDA+U?and density functional theory combined with dynamic mean field theory?DFT+DMFT?.We firstly calculated the total energy of different magnetic configurations and obtained a new metastable lower energy magnetic structure named as QAFM.The new lower magnetic structure breaks the C₄ symmetry in both aspects of structure and charge density,which may result in the formation of a nematic phase.We further investigated the correlation effect on the electronic properties of monolayer FeSe.The single-layer FeSe magnetic ground state—the double checkerboard antiferromagnetic state?OAFM?has undergone a great change in the electronic properties after considering the correlation effect of Fe-d orbitals.In the case of fully optimized structure,a open-close-reopen of band gap occurs after the Coulomb interaction U is added.Moreover,the effect of Coulomb interaction U on the Fe d-orbital electrons is different near the Fermi level,and leads to a orbital selectivity.Additionally,when the Coulomb interaction U is small,the Hund coupling interaction J has a great influence on the electronic properties of the FeSe in OAFM state,and when U increases,the influence of J on its electronic properties is gradually weaken.In our research,the discovery of new metastable magnetic order has an important significance for explaining the origin of the nematic phase of FeSe at low temperature,and the study of FeSe correlation effect is also helpful to reveal finally the mechanism of unconventional high temperature superconductivity.