Berlin 2024 – scientific programme

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MA: Fachverband Magnetismus

MA 10: Electron Theory of Magnetism and Correlations/Other Theory

MA 10.6: Talk

Monday, March 18, 2024, 16:15–16:30, EB 107

Two-particle self-consistent approach for broken symmetry phases — •Lorenzo Del Re — Max-Planck-Institute for Solid State Research, 70569 Stuttgart, Germany

Spontaneous symmetry breaking of interacting fermion systems constitutes a major challenge for many-body theory due to the proliferation of scattering channels once degenerate in the symmetric phase. One example is given by the ferro/antiferromagnetic broken symmetry phase (BSP) of the Hubbard model, where vertices in the spin-transverse and spin-longitudinal channels become independent with a consequent increase in the computational power for their calculation.

Here we generalize the formalism of the non-perturbative Two-Particle-Self-Consistent method (TPSC) to treat broken SU(2) magnetic phases of the Hubbard model. We show how in the BSP, the sum-rule enforcement of susceptibilities must be accompanied by a modified gap equation resulting in a renormalisation of the order parameter, vertex corrections and the preservation of the gap-less feature of the Goldstone modes.

We then apply the theory to the antiferromagnetic phase of the 3D-Hubbard model in the cubic lattice at half-filling. We compare our results of double occupancies and staggered magnetisation to the ones obtained using Diagrammatic Monte Carlo showing good quantitative agreement between the two methods.

We argue how vertex corrections play a central role in lowering the Higgs resonance with respect to the quasi-particle excitation gap in the spin-longitudinal susceptibility, yielding a well visible Higgs-mode.

Keywords: Hubbard model; Strongly correlated electron systems; TPSC; Vertex corrections; Higgs mode