Polaronic metal in lightly doped high-Tc cuprates
  We present a combined study of the angle-resolved-photoemission spectroscopy (ARPES) and quantum Monte Carlo simulations to propose a novel polaronic metallic state in underdoped cuprates. An approximation scheme is proposed to represent underdoped cuprates away from 1/2 filling, replacing the many-body Hamiltonian by that of a single polaron with effective electron-phonon interaction (EPI), that successfully explains many puzzles such as a large momentum-dependent dichotomy between nodal and anti-nodal directions, and an unconventional doping dependence of ARPES in the underdoped region. 
A. S. Mishchenko, N. Nagaosa, K. M. Shen, Z.-X. Shen, X. J. Zhou and   T. P. Devereaux
cond-mat.str-el