Abstract We apply to underdoped cuprates our FL* (fractionalized Fermi Liquid) formalism, where in addition to the standard holes other quasi-particle excitations are (semionic) holons that only carry charge and gapped spinons that only carry spin, interacting via a slave-particle gauge field. We first apply this approach to the “pseudogap phase” and we show that the slave-particle gauge interaction binds the holon and the spinon into a hole resonance whose spectral weight is essentially concentrated on Fermi arcs. Furthermore the self-energy of the hole exhibits what we call a Marginal FL* behaviour, i.e. the relaxation rate of the hole at zero temperature and small energy is proportional to the absolute value of the energy, measured from the Fermi surface. Along the nodal direction such behaviour combined with an additional Fermi liquid contribution is shown to be in agreement with many experimental data. We then apply the FL* formalism in the superconducting region of the doping-temperature phase diagram below the "pseudogap phase". There we show the appearance of a magnetic excitation, that we call magnon, as a spinon-antispinon resonance whose spectral weight exhibits a hourglass structure, qualitatively in agreement with neutron experiments. This structure appears as a consequence of a finite density of RVB spinon pairs and the slave-particle gauge attraction between unpaired spinons and antispinons.
P. A. Marchetti (2026) studied this question.