On the stability of polaronic superlattices in strongly coupled   electron-phonon systems
  We investigate the interplay of electron-phonon (EP) coupling and strong electronic correlations in the frame of the two-dimensional (2D) Holstein t-J model (HtJM), focusing on polaronic ordering phenomena for the quarter-filled band case. The use of direct Lanczos diagonalization on finite lattices allows us to include the effects of quantum phonon fluctuations in the calculation of spin/charge structure factors and hole-phonon correlation functions. In the adiabatic strong coupling regime we found evidence for ``self-localization'' of polaronic carriers in a $(\pi,\pi)$ charge-modulated structure, a type of superlattice solidification reminiscent of those observed in the nickel perovskites $La_{2-x}Sr_{x}NiO_{4+y}$. 
G. Wellein, H. Fehske, H. B\"uttner, A. R. Bishop