On a repulsive quasi-spin model

M. J. Bhaseen, Fabian H. L. Eßler, Anja Grage

We consider spin correlations in the one-dimensional (1D) half-filled repulsive Hubbard model. For very large values of the on-site repulsion $U$ the spin correlations are dominated by virtual hopping processes of electrons and are described in terms of a spin-$1∕2$ Heisenberg chain. As $U$ is decreased real hopping processes of electrons become important and eventually dominate the spin response. We discuss the evolution of the dynamical structure factor as a function of $U$. We comment on the relevance of our results for inelastic neutron-scattering experiments on quasi-1D materials.

M. C. Cambiaggio, Angelo Plastino

Nikolai Nikolaevich Bogoliubov, A.S. Shumovsky

Nitin Kaushal, Marcel Franz

We study the emergence of altermagnetism from repulsive interactions for electrons on the Lieb lattice as a model of quasi-2D oxychalcogenides with the so-called "anti-CuO_{2}" lattice structure. A comprehensive study of the Lieb lattice Hubbard model, using unrestricted Hartree-Fock and exact diagonalization techniques, establishes the presence of a spin-1/2 altermagnetic Mott insulating ground state for average electron densities of 2 and 4 per unit cell. Both phases show the characteristic spin splitting in the electron bands as well as in the magnon bands, as indicated by solutions of an effective spin-1/2 Heisenberg model that we construct. We also provide evidence for altermagnetic metal formation in the electron- and hole-doped Mott state, giving rise to Fermi surfaces with d_{x^{2}-y^{2}}-wave spin splitting and quasi-one-dimensional characteristics.

Stanislav Alekseevich Molchanov, Nguyen The Long

H Aghahosseini, John B. Parkinson

The ground state in the spin-flop phase is investigated by means of numerical calculations of the static correlation functions for short chains of up to 12 atoms. In the light of these results the authors suggest a picture in which the deviations form extended quasi-particles with an effective long range repulsive interaction. The model gives reasonable results for the magnetisation as a function of field and for the spin wave spectrum in the spin-flop phase.