Gauge approach to the 'pseudogap' phenomenology of the spectral weight in high Tc cuprates

We assume the t–t'–J model to describe the CuO2 planes of hole-doped cuprates and we adapt the spin–charge gauge approach, previously developed for the t–J model, to describe the holes in terms of a spinless fermion carrying the charge (holon) and a neutral boson carrying spin 1/2 (spinon), coupled by a slave-particle gauge field. In this framework we consider the effects of a finite density of incoherent holon pairs in the normal state. Below a crossover temperature, identified as the experimental 'upper pseudogap', the scattering of the 'quanta' of the phase of the holon-pair field against holons reproduces the phenomenology of nodal Fermi arcs coexisting with a gap in the antinodal region. We thus obtain a microscopic derivation of the main features of the hole spectra due to the pseudogap. This result is obtained through a holon Green function which follows naturally from the formalism and analytically interpolates between a Fermi liquid-like and a d-wave superconductor behaviour as the coherence length of the holon-pair order parameter increases. By inserting the gauge coupling with the spinon we construct explicitly the hole Green function and calculate its spectral weight and the corresponding density of states. So we prove that the formation of holon pairs induces a depletion of states on the hole Fermi surface. We compare our results with ARPES and tunnelling experimental data. In our approach the hole preserves a finite Fermi surface until the superconducting transition, where it reduces to four nodes. Therefore we propose that the gap seen in the normal phase of cuprates is due to the thermal broadening of the SC-like peaks masking the Fermi-liquid peak in the spectral weight. The Fermi arcs then correspond to the region of the Fermi surface where the Fermi-liquid peak is unmasked.