Many qualitative features (e.g. hourglass structure and presence vs absence of the “resonance”) of neutron experiments on the spin excitation (here called magnon) in several hole-underdoped superconducting (SC) cuprates (YBCO [1],LSCO[2], Hg1201) can be recovered within a FL* approach based on a 2D t-t'-J model [3] using few phenomenological parameters independent of temperature (T) , energy (E) and doping (p). Our FL* satisfies a topological version of Luttinger's theorem, and besides standard holes, the quasiparticle excitations are gapless, charged spinless holons and gapped, neutral, with spin1/2 spinons interacting via a slave-particle gauge field. We apply the FL* formalism to the SC region of the p-T phase diagram below the "pseudogap phase". There we show the appearence of the magnon as a spinon-antispinon bound state. Its spectral weight exhibits an hourglass structure, due to a finite density of RVB spinon pairs in the SC state, and its self-energy exhibits a "Marginal Fermi Liquid (MFL)" behavior, due to the slave-particle attraction between unpaired spinons and antispinons. The appearence of the "resonance" is controlled by adding a phenomenological term describing the effect of the stripes, but still with self-energy of MFL type.

[1] V. Hinkov et al., Nat. Phys. 3, 780 (2007)

[2] B. Vignolle et al., Nat Phys. 3, 163 (2007)

[3] P.A. Marchetti et al., PRB 84, 214525 (2011); P.A. Marchetti, J. Superc. Nov. Magn. 39:48 (2026)