Hubbard-model description of the high-energy spin-weight distribution in La2CuO4

Abstract

The spectral-weight distribution in recent neutron scattering experiments on the parent compound La2CuO4 (LCO), which are limited in energy range to about 450 meV, is studied in the framework of the Hubbard model on the square lattice with effective nearest-neighbor transfer integral t and on-site repulsion U. Our study combines a number of numerical and theoretical approaches, including, in addition to standard treatments, density matrix renormalization group calculations for Hubbard cylinders and a suitable spinon approach for the spin excitations. The latter spin-1/2 spinons are the spins of the rotated electrons that singly occupy sites. These rotated electrons are mapped from the electrons by a uniquely defined unitary transformation, in which rotated-electron single and double occupancy are good quantum numbers for finite interaction values. Our results confirm that the U/8t magnitude suitable to LCO corresponds to intermediate U values smaller than the bandwidth 8t , which we estimate to be 8t ≈ 2.36 eV for U/8t ≈ 0.76. This confirms the unsuitability of the conventional linear spin-wave theory. Our theoretical studies provide evidence for the occurrence of ground-state d-wave spinon pairing in the half-filled Hubbard model on the square lattice. This pairing applies only to the rotated-electron spin degrees of freedom, but it could play a role in a possible electron d-wave pairing formation upon hole doping. We find that the higher-energy spin spectral weight extends to about 566 meV and is located at and near the momentum [π,π]. The continuum weight energy-integrated intensity vanishes or is extremely small at momentum [π,0]. This behavior of this intensity is consistent with that of the spin waves observed in recent high-energy neutron scattering experiments, which are damped at the momentum [π,0].We suggest that future LCO neutron scattering experiments scan the energies between 450 and 566 meV and momenta around [π,π].