Localization in a t-J-Type Model with Translational Symmetry.

An explicit spatial localization of a hole is shown in a two-leg t-J ladder in the presence of a staggered chemical potential, which still retains translational symmetry, by the density matrix renormalization group method. Delocalization can be recovered in the following cases, where either the hidden phase string effect is turned off or a finite next-nearest-neighbor hopping t^{'} is added to sufficiently weaken the phase string effect. In addition, two holes are always delocalized by forming a mobile bound pair, in contrast to the localized single holes, which points to a novel pairing mechanism as one of the essential properties of a doped Mott insulator.