Localization in a t − J type ladder 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 density matrix renormalization group method. Delocalization can be recovered in following cases, in which either the hidden phase string effect is turned off or a finite next-neighbor hopping t′ is added to sufficiently weaken the phase string effect. In particular, two holes are always delocalized by forming a mobile bound pair in contrast to the localized single holes, pointing to a novel pairing mechanism of strong correlation nature.