Polaronic effects in the lightly doped cuprates

Kyle Shen

Department of Applied Physics, Stanford University, McCullough 433, 476 Lomita Mall, Stanford 94305, USA

The ability of ARPES to study the interactions of electrons with other degrees of freedom has made it an ideal tool for studying the microscopic properties of strongly interacting systems. Such strong couplings can often result in situations where the true eigenstates of the system are polaronic with an extremely small quasiparticle residue, Z. Here, we discuss this scenario in relation to the cuprate superconductors, particularly the Ca2-xNaxCuO2Cl2 family. We find that ARPES data from the undoped Mott insulator, Ca2CuO2Cl2, can be well explained within a polaronic Franck-Condon broadening model, together with the evolution of the chemical potential and quasiparticle-like excitations as a function of doping. Comparison of the lineshape and temperature dependence of the lower Hubbard band with valence band states in the undoped system suggests that this effect arises primarily from lattice polaron formation. Our work provides a new approach to analyzing and understanding ARPES spectra from the lightly doped and undoped cuprates in the context of strong electron-boson interactions.