Temperature dependence of correlated electronic states in archetypal kagome metal CoSn

Abstract: Hexagonal CoSn is a newly-discovered frustrated kagome metal. It shows close-to-textbook flat bands and orbital-selective Dirac fermions, which are largely associated with its strongly correlated Co-3$d$ orbitals. Because correlated electronic states are easily regulated by external conditions (such as chemical doping, pressure, and temperature), the fate of these kagome-derived electronic bands upon temperature becomes an interesting and unsolved question. In this work, we try to study the temperature-dependent electronic structures of hexagonal CoSn by means of the density functional theory in conjunction with the embedded dynamical mean-field theory. We find that hexagonal CoSn is in close proximity to a Mott insulating state at ambient condition. Special attention is devoted to the evolution of its Co-3$d$ electronic states with respect to temperature. At least six different temperatures (or energy scales), namely $T^{*}$, $T_{\text{FL}}$, $T_{\text{S1}}$ (and $T_{\text{S2}}$), $T_{\text{SF}}$, and $\bar{T}$, are figured out. They are related to stabilization of the "pseudogap" state, emergence of the non-Fermi-liquid phase, onset (and completeness) of the intermediate spin state, occurrence of the spin-frozen phase, beginning of the orbital freezing transition, respectively.