Photodynamics of optical excitations in Mott insulators via differential optical conductivity

We examine the nonequilibrium optical response of the one-dimensional half-filled extended Hubbard model to a pump field pulse. We derive, compute, and analyze the differential optical conductivity, which is related to the time-resolved optical conductivity: a key quantity in pump and probe spectroscopy experiments. Using time-dependent density matrix renormalization group, we calculate the differential optical conductivity and detect a concurrent photoexcitation of doublons and holons along with a reduction of the local magnetic moment and antiferromagnetic correlations. The differential optical conductivity exhibits two main features: (1) photogeneration of mid-gap spectral weight associated to parity-forbidden optical states, and (2) melting of the excitonic peak and emergence of a Fano-like optical resonance due to quantum interference of the excitons and the absorption band. The resulting nonequilibrium optical excitations correspond to renormalized excitonic strings, excitons, or unbound doublon-holon pairs, upon decreasing of intersite Coulomb repulsion, respectively. Our results have direct relevance to pump and probe spectroscopy experiments in the THz domain performed on organic salts such as ET-F₂TCNQ, where quantum interference between excitons and absorption-band states give rise to nonequilibrium optical excitations and photometallization.