Spin and charge modulations in a single-hole-doped Hubbard ladder: Verification with optical lattice experiments

Abstract

We show that pronounced modulations in spin and charge densities can be induced by the insertion of a single hole in an otherwise half-filled two-leg Hubbard ladder. Accompanied with these modulations is a loosely bound structure of the doped charge with a spin-1/2, in contrast to the tightly bound case where such modulations are absent. These behaviors are caused by the interference of the Berry phases associated with a string of flipped spins (or "phase strings") left behind as a hole travels through a spin bath with a short-range antiferromagnetic order. The key role of the phase strings is also reflected in how the system responds to increasing spin polarization and the on-site repulsion, addition of a second hole, and increasing asymmetry between intra-and interchain hopping. Remarkably, all these properties persist down to ladders as short as ∼10 sites, as the smoking gun of the phase-string effect. They can therefore be studied in cold-atom experiments using the recently developed fermion microscope.

On the possibility of many-body localization in a doped Mott insulator

“…As shown in Fig. 2 in the single hole case, all the Nagaoka polaron states (with S > 1/2) disappear in the so-called σ -Hubbard model 34 , in which only a conventional quasiparticle phase survives (cf. the smooth dashed curve in Fig.…”

“…By contrast, the Nagaoka polaron phases shown in Fig. 2 disappear in the so-called σ -Hubbard model 34 , as shown by the dashed curve, where the doped hole remains a conventional quasiparticle throughout the accessible regime of β . This σ -Hubbard model has been previously studied in ref.…”

“…This σ -Hubbard model has been previously studied in ref. 34 , which differs from the Hubbard model by a Berry-like phase 33 (phase string) as to be discussed in Sec. II E below.…”

“…However, once or by turning off the phase string in the σ -Hubbard model 34 (see Sec. II E), the pair binding and localization simultaneously collapse, as shown in Fig.…”

“…As such, the charge sector of lightly doped Hubbard model with sufficiently large but finite U has an emergent MBL violating ETH and with spontaneous translational symmetry breaking in finite energy-density states. Further, an eigenstate phase transition to a conventional delocalized phase has been found by increasing the anisotropy of the hopping integrals of the ladder or by turning off the so-called phase strings 33 34 as the intrinsic Berry phase of the Hubbard model.…”