Temperature dependence of correlated electronic states in the archetypal kagome metal CoSn

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 $3d$ 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 the Co $3d$ electrons are in close proximity to Mott insulating states at ambient condition. Special attention is devoted to the evolution of Co $3d$ electronic states with respect to temperature. At least six different temperatures (or energy scales), namely T*, TFL, TS1 (and TS2), TSF, and T̄, are figured out. They are related to stabilization of the ``pseudogap'' state, emergence of the non-Fermi-liquid phase, onset (and completeness) of the spin plateau, occurrence of the spin-frozen phase, and beginning of the orbital freezing transition, respectively.