We present a compelling response of a low-dimensional strongly correlated system to an external perturbation. Using the time-dependent Lanczos method we investigate a nonequilibrium evolution of the half-filled one-dimensional extended Hubbard model, driven by a transient laser pulse. When the system is close to the phase boundary, by tuning the laser frequency and strength, a sustainable charge order enhancement is found that is absent in the Mott insulating phase. We analyze the conditions and investigate possible mechanisms of emerging charge order enhancement. Feasible experimental realizations are proposed.
A numerical method to calculate optical conductivity based on a pump-probe setup is presented.Its validity and limits are tested and demonstrated via concrete numerical simulations on the halffilled one-dimensional extended Hubbard model both in and out of equilibrium. By employing either a steplike or a Gaussian-like probing vector potential, it is found that in nonequilibrium, the method in the narrow-probe-pulse limit can be identified with variant types of linear response theory, which, in equilibrium, produce identical results. The observation reveals the underlying probe-pulse dependence of the optical conductivity calculations in nonequilibrium, which may have applications in the theoretical analysis of ultrafast spectroscopy measurements.
We investigate time evolution of optical conductivity in the half-filled one-dimensional extended Hubbard model driven by a transient laser pulse, by using the time-dependent Lanczos method. Photoinduced in-gap excitations exhibit qualitatively different structure in the spin-density wave (SDW) in comparison to the charge-density wave (CDW) phase. In the SDW, the origin of a lowenergy in-gap excitation is attributed to even-odd parity of photoexcited states, while in the CDW an in-gap state is due to confined photo-generated carriers. The signature of the in-gap excitations can be identified as a characteristic oscillation in the time evolution of physical quantities.
Abstract:The electronic structures and optical properties of the monoclinic ZrO 2 (m-ZrO 2 ) are investigated by means of first-principles local density approximation (LDA) + U approach. Without on-site Coulomb interactions, the band gap of m-ZrO 2 is 3.60 eV, much lower than the experimental value (5.8 eV). By introducing the Coulomb interactions of 4d orbitals on Zr atom (U d ) and of 2p orbitals on O atom (U p ), we can reproduce the experimental value of the band gap. The calculated dielectric function of m-ZrO 2 exhibits a small shoulder at the edge of the band gap in its imaginary part, while in the tetragonal ZrO 2 and cubic ZrO 2 it is absent, which is consistent with the experimental observations. The origin of the shoulder is attributed to the difference of electronic structures near the edge of the valence and conduction bands.
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