Self-localization of a single hole in Mott antiferromagnets

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Anderson localization - quantum suppression of carrier
diffusion due to disorders - is a basic notion of modern condensed matter
physics. Here I will talk about a novel localization phenomenon totally
contrary to this common wisdom. Strikingly, it is purely of strong interaction
origin and occurs without the assistance of disorders. Specifically, by
combined numerical (density matrix renormalization group) method and analytic
analysis, we show that a single hole injected in a quantum antiferromagnetic
ladder is generally self-localized even though the system respects the
translational symmetry. The localization length is found to monotonically
decrease with the increase of leg number, indicating stronger self-localization
in the two-dimensional limit. We find that a peculiar coupling between the
doped charge and the quantum spin background causes quantum interference among
different hole paths. The latter brings the hole's itinerant motion to a halt,
a phenomenological analogy to Anderson localization. Our findings are opposite
to the common belief of the quasiparticle picture for the doped hole and unveil
a completely new paradigm for lightly doped Mott insulators.