Magnons in multiorbital Hubbard models, from Lieb to kagome

TL;DR

This paper explores magnetic orders and excitations in a half-filled Hubbard model that transitions between Lieb and kagome lattices, revealing diverse magnetic states and excitation spectra through advanced theoretical methods.

Contribution

It introduces a comprehensive phase diagram for the Lieb-kagome lattice Hubbard model, identifying magnetic phases and excitation spectra using combined Hartree-Fock and Bethe-Salpeter approaches.

Findings

Identification of various magnetic phases including ferrimagnetic and antiferromagnetic states.

Discovery of gapped Higgs magnon bands from amplitude fluctuations.

Mapping of the U-t' phase diagram with detailed magnetic excitation spectra.

Abstract

We investigate the magnetic orders and excitations in a half-filled Hubbard model that continuously interpolates between the Lieb and kagome lattices. Using self-consistent Hartree-Fock approximation combined with real-time two-particle response functions from the Bethe-Salpeter equation in the random phase approximation, we map the $U-t'$ phase diagram of the Lieb-kagome lattices, identifying the typical magnetic states and the corresponding magnetic excitation spectra. In addition to gapless Goldstone magnons, the ferrimagnetic and antiferromagnetic symmetry-broken phases also exhibit gapped Higgs magnon bands, which originate from amplitude fluctuations in the order parameter characterizing spontaneous symmetry breaking.