Photoemission and optical experiments indicate that the transition to superconductivity in cuprates is an
'undressing' transition . In photoemission this is seen as a coherent quasiparticle peak emerging from an
incoherent background, in optics as violation of the Ferrell-Glover-Tinkham sum rule indicating effective
mass reduction of superconducting carriers. We propose that this is a manifestation of the fundamental
electron-hole asymmetry of condensed matter described by the theory of hole superconductivity. The theory
asserts that electrons in nearly empty bands and holes in nearly full bands are fundamentally different : the
former yield high conductivity and normal metals, the latter yield low normal state conductivity and high
temperature superconductivity. This is because the normal state transport of electrons is coherent and that of
holes is incoherent. We explain how this asymmetry arises from the Coulomb interaction between electrons
in atoms and the nature of atomic orbitals, and propose a simple Hamiltonian to describe it. A $universal$
mechanism for superconductivity follows from this physics, whereby dressed hole carriers undress by
pairing, turning (partially) into electrons and becoming more mobile in the superconducting state.
Return