Relaxation of strongly coupled electron and phonon fields after photoemission and high-energy part of ARPES spectra of cuprates

Abstract

An approach to considering systems with a high concentration of correlated carriers and strong long-range electron-phonon interaction and to calculating the high-energy part of the angle-resolved photoemission spectroscopy (ARPES) spectra of such systems is suggested. Joint relaxation of strongly coupled fields-a field of correlated electrons and phonon field-after photoemission is studied to clarify the nature of characteristic features observed in the high-energy part of the ARPES spectra of cuprate superconductors. Such relaxation occurs in systems with strong predominantly long-range electron-phonon interaction at sufficiently high carrier concentration due to the coexistence of autolocalized and delocalized carriers. A simple method to calculate analytically a high-energy part of the ARPES spectrum arising is proposed. It takes advantage of using the coherent states basis for the phonon field in the polaron and bipolaron states. The approach suggested yields all the high-energy spectral features like broad Gaussian band and regions of 'vertical dispersion' being in good quantitative agreement with the experiments on cuprates at any doping with both types of carriers. Demonstrated coexistence of autolocalized and delocalized carriers in superconducting cuprates changes the idea about their ground state above the superconducting transition temperature that is important for understanding transport and magnetic properties. High density of large-radius autolocalized carriers revealed may be a key to the explanation of charge ordering in doped cuprates.

Strong long-range electron–phonon interaction as possible driving force for charge ordering in cuprates

“…The strongest Coulomb on-site interaction and exchange interaction of carriers on neighboring sites considered theoretically with the help of Hubbard and t-J models are taken into account in the effective mass approximation, analogously to the way successfully applied in calculating the highenergy part of the ARPES spectra of the systems under study [26]. In such approach the dispersion of the Lower and Upper Hubbard bands (LHB and UHB) determined by (among other factors) charge and spin correlations is taken from the ARPES spectra as described in [26] and used to calculate the carrier effective mass near the bottom of both bands and the top of the LHB. It is possible since the ARPES band dispersion at strong EPI and low doping with holes follows the 'bare' carrier dispersion (i.e.…”

“…It is possible since the ARPES band dispersion at strong EPI and low doping with holes follows the 'bare' carrier dispersion (i.e. without EPI) [15,16,26] shifted much deeper along the binding energy axis. Close values of the effective mass result from the calculated in the Hubbard and t-J models carrier dispersion [33].…”

“…Cold carriers obey the distribution over wavepacket states, in the system's ground state they all are in ASs [29]. A bright illustration of this dichotomy of the carriers' momentum space is 'vertical dispersion' observed in the highenergy part of ARPES spectra of cuprates at the momentum k 0 [26]. As here we study primarily systems with high carriers density we will consider below ASs of only bipolaron type.…”

“…Recently it has been demonstrated that strong Frohlich EPI and high density of correlated carriers can result in the HEA in ARPES spectra of cuprates [26]. Namely, division of the momentum space between autolocalized and delocalized carriers (according to Pauli exclusion rule) results in 'waterfalls' in the ARPES spectrum due to different energetic cost of the system relaxation after photoemission from these two types of states.…”

“…Namely, division of the momentum space between autolocalized and delocalized carriers (according to Pauli exclusion rule) results in 'waterfalls' in the ARPES spectrum due to different energetic cost of the system relaxation after photoemission from these two types of states. The momentum position of 'waterfall' in cuprates related with the ASs size [26] reveals that at high carrier density it is smaller than the size of single bipolaron. This also shows necessity of studying the ground state of systems with strong Frohlich EPI and high carriers density.…”