Abstract
The t-J-U model of high-Tc copper-oxide superconductors incorporates both the on-site Coulomb repulsion and kinetic exchange interaction and yields a semi-quantitative description of the static properties of those materials. We extend this analysis to dynamic quantities and address collective spin- and charge excitations in the correlated metallic state of the t-J-U model. We employ VWF+1/Nf approach that combines the variational wave function (VWF) approach with the expansion in the inverse number of fermionic flavors (1/Nf). It is shown that the resonant (paramagnon) contribution to the dynamic magnetic susceptibility remains robust as one interpolates between the Hubbard- and t-J-model limits, whereas the incoherent continuum undergoes substantial renormalization. Energy of the collective charge mode diminishes as the strong-coupling limit is approached. We also introduce the concept of effective kinetic exchange interaction that allows for a unified interpretation of magnetic dynamics in the Hubbard, t-J, and t-J-U models. The results are discussed in the context of recent resonant inelastic x-ray scattering experiments for the high-Tc cuprates.
Highlights
High-temperature copper-oxide superconductors (SC) serve as paradigmatic strongly-correlated systems, evolving from the antiferromagnetic (AF) Mott insulating state, through high-Tc SC state, to normal metal phase as a function of chemical doping
The t-J-U-model studies have been hitherto restricted to static properties, whereas recent developments in spectroscopic techniques (in particular, resonant inelastic x-ray scattering (RIXS)) provide comprehensive evi dence for the relevance of collective excitations across the phase dia gram of high-Tc cuprates [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28]
We employ VWF+1/N f scheme [30,31,32], combining Variational Wave Function (VWF) approach in its diagram matic form with the field-theoretical 1/N f expansion (N f denotes the number of fermionic flavors)
Summary
High-temperature (high-Tc) copper-oxide superconductors (SC) serve as paradigmatic strongly-correlated systems, evolving from the antiferromagnetic (AF) Mott insulating state, through high-Tc SC state, to normal metal phase as a function of chemical doping. The t-J-U-model studies have been hitherto restricted to static properties, whereas recent developments in spectroscopic techniques (in particular, resonant inelastic x-ray scattering (RIXS)) provide comprehensive evi dence for the relevance of collective excitations across the phase dia gram of high-Tc cuprates [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28] In this respect, the t-J-U model remains largely unexplored and is yet to be tested as a tool to study many-particle dynamics. We employ VWF+1/N f scheme [30,31,32], combining Variational Wave Function (VWF) approach in its diagram matic form with the field-theoretical 1/N f expansion (N f denotes the number of fermionic flavors) The latter has been recently benchmarked [31] against determinant quantum Monte-Carlo for small systems. This analysis supports the t-J-U model as a tool to study semi-quantitatively collective modes in high-Tc cuprates
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