Understanding pseudogaps in high Tc materials

We begin with the observation that acoustic bands and carrier bands cross on an interesting 1D manifold for 2D materials. The reason is that the acoustic band rises linearly from the Gamma point k=0, while the carrier band rises quadratically. The carrier band catches up to the phonon dispersion at higher k. The existence of this intersection is apparently missing in the literature. It is also buried deep in the Fermi sea for normal metals and unimportant. However this crossing becomes important for the emerging carrier bands in low doped cuprates. At every point on the intersection manifold, both phonon and carrier have the same frequency (energy) and the same wavelength, setting up a strong resonance. This resonance disrupts the carrier bands wherever this 1D track crosses them, causing gaps. Wherever the ''gap track'', as we call it, crosses the Fermi surface, probes like ARPES will find the carrier density simply missing - a gap. The rest of the Fermi surface not crossed by the gap track survives. Thus the Fermi arcs are naturally surviving segments of the usual Fermi surface. The spectral intensitiy is conserved, but cast far and wide, and the gap gives the appearance of being uncompensated. This talk will present strong evidence that these gap tracks agree with and explain the gap patterns seen in photoemission and ARPES. The phonon-carrier intersection gives rise to an avoided crossing and a new quasiparticle which we call a ''vibron''. The whole scenario is in perfect analogy to polariton physics, with the role of photon being played by the phonon. The mechanism we find also strongly suggests a path to incommensurate charge density waves.