Pressure suppression of electron correlation in the collapsed tetragonal phase of CaFe2As2: A DFT-DMFT investigation

Recent studies reveal a pressure induced transition from a paramagnetic tetragonal phase (T) to a collapsed tetragonal phase (CT) in CaFe2As2, which was found to be superconducting with pressure at low temperature. We have investigated the effects of electron correlation and a local fluctuating moment in both tetragonal and collapsed tetragonal phases of the paramagnetic CaFe2As2 using self-consistent DFT-DMFT with continuous time quantum Monte Carlo as the impurity solver. From the computed optical conductivity, we find a gain in the optical kinetic energy due to the loss in Hund's rule coupling energy in the CT phase. We find that the transition from T to CT turns CaFe2As2 from a bad metal into a good metal. Computed mass enhancement and local moments also show a significant decrease in the CT phase, which confirms the suppression of the electron correlation in the CT phase of CaFe2As2.