TY  - JOUR
PB  - SciPost Foundation
DO  - 10.21468/SciPostPhys.18.3.077
TI  - Two-particle self-consistent approach for broken symmetry phases
PY  - 2025/03/03
UR  - https://www.scipost.org/SciPostPhys.18.3.077
JF  - SciPost Physics
JA  - SciPost Phys.
VL  - 18
IS  - 3
SP  - 077
A1  - Del Re, Lorenzo
AB  - Spontaneous symmetry breaking of interacting fermion systems constitutes a major challenge for many-body theory due to the proliferation of new independent scattering channels once absent or 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. We generalise the non-perturbative Two-Particle-Self-Consistent method (TPSC) to address broken SU(2) magnetic phases in the Hubbard model, offering an efficient approach that incorporates strong correlations. We show that 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 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 excellent quantitative agreement. We demonstrate 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.
ER  -

@Article{10.21468/SciPostPhys.18.3.077,
	title={{Two-particle self-consistent approach for broken symmetry phases}},
	author={Lorenzo Del Re},
	journal={SciPost Phys.},
	volume={18},
	pages={077},
	year={2025},
	publisher={SciPost},
	doi={10.21468/SciPostPhys.18.3.077},
	url={https://scipost.org/10.21468/SciPostPhys.18.3.077},
}