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Pseudogap in the c-axis (along the ladder) optical conductivity of t - J ladders and its quasiparticle interpretation



Rok publikování 2019
Druh Článek v odborném periodiku
Časopis / Zdroj Journal of Physics: Condensed Matter
Fakulta / Pracoviště MU

Přírodovědecká fakulta

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Klíčová slova optical response; two-leg ladder; t - J model; pseudogap; cuprate superconductors
Popis Motivated by similarities between cuprate superconductors and two-leg ladder copper-oxide compounds and in order to obtain a better understanding of optical properties of cuprate superconductors we have studied the c-axis (along the ladder) optical conductivity sigma(omega) of a doped t(parallel to) - t(perpendicular to) - J(parallel to) - J(perpendicular to) two-leg ladder. Using exact diagonalization, we have calculated the conductivity and related quantities for cyclic ladders of up to 13 rungs. In agreement with results of an early study by Hayward and coworkers (Hayward et al 1996 Phys. Rev. B 53 8863) we find that sigma(omega) consists of a Drude peak at zero frequency and an absorption band in the infrared region that is separated from the former by a pseudogap. The width of the pseudogap E-pG increases with increasing J/t, in parallel with an increase of the magnitude E-QP of the gap in the quasiparticle excitation spectra. Our central finding is that E-PG approximate to E-QP + Delta(s), where Delta(s) is the magnitude of the gap in the spin excitation spectra. We demonstrate that this approximate relation can be understood in terms of a phenomenological model involving a superconducting ladder and a coupling between charged quasiparticles and spin excitations. The relation is remarkably similar to the one between experimental values of the energy scale of a dip in the in-plane optical conductivity, the superconducting gap 2 Delta and the energy of the spin-resonance in cuprate superconductors (for a recent discussion of the optical data, see Sopik et al 2015 New J. Phys. 17 053022). Our findings support the point of view that low energy infrared active excited states of cuprate superconductors can be viewed as consisting of two charged quasiparticles connected with pair-breaking and a spin excitation.
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