RIKEN-Japan
The angle resolved photoemission spectra (ARPES) and optical conductivity (OC) of the underdoped high temperature superconductors is studied in the framework of the low density limit of the t-J-Holstein model in which hole in the antiferromagnetic background is coupled to optical phonons. It is shown that both magnetic excitations of the t-J model and strong coupling to phonons are important to explain the ARPES and OC in the underdoped compounds. Strong coupling to phonons leads to the transfer of the spectral weight of ARPES from the narrow quasiparticle peak to the broad Franck-Condon shake-off band which maximum, nevertheless, copies dispersion of a hole in the pure t-J model without coupling to phonons [1]. The infrared OC of the underdoped compounds reveal, both in theory and experiment, the two band structure with low energy band arising due to phonon scattering and high energy peak emerging because of complex process of simultaneous emission of magnon and several phonons [2]. Both t-J and Holstein model fail to describe anomalous temperature dependence of ARPES whereas the t-J-Holstein model is in semi quantitative agreement with experiment [3]. Further generalization of the model to nonlocal electron-phonon couplings is considered [4]. It is shown that analysis of ARPES and OC data for larger dopings suggests fast decrease of the electron-phonon coupling strength with doping having universal dependence of the coupling strength on the in-plain hole doping concentration [2].
[1] A. S. Mishchenko, N. Nagaosa, Phys. Rev. Lett, 93 036402 (2004)
[2] A. S. Mishchenko et al, Phys. Rev. Lett, 100 166401 (2008)
[3] V. Cataudella et al, Phys. Rev. Lett, 99 226402 (2007)
[4] G. De Filippis et al, Phys. Rev. Lett, 99 146405 (2007)