Superconductivity from undressing

Photoemission experiments in high-$T_c$ cuprates indicate that quasiparticles are heavily “dressed” in the normal state, particularly in the low doping regime. Furthermore, these experiments show that a gradual undressing occurs both in the normal state as the system is doped and the carrier concentration increases, as well as at a fixed carrier concentration as the temperature is lowered and the system becomes superconducting. A similar picture can be inferred from optical experiments. It is argued that these experiments can be simply understood with the single assumption that the quasiparticle dressing is a function of the local carrier concentration. Microscopic Hamiltonians describing this physics are discussed. The undressing process manifests itself in both the one- and two-particle Green’s functions, and hence leads to observable consequences in photoemission and optical experiments, respectively. An essential consequence of this phenomenology is that the microscopic Hamiltonians describing it break electron-hole symmetry: these Hamiltonians predict that superconductivity will only occur for carriers with holelike character, as proposed in the theory of hole superconductivity.