Interference of Holon Strings in 2D Hubbard Model

TL;DR

This paper investigates holon strings in the 2D Hubbard model, revealing how their interference affects spin correlations and magnetic order, with implications for observing spin-charge separation in cold atom experiments.

Contribution

It identifies the Marshall phase of holon strings as observable via spin correlations and demonstrates how interference influences holon propagation and magnetic order.

Findings

Holon strings' interference causes anisotropic holon propagation.

Large suppression of magnetic order occurs along holon paths.

Marshall phase effects can be observed through spin correlation measurements.

Abstract

The 2D Hubbard model with large repulsion is a central and yet unsolved problem in condensed matter physics for decades. The challenge appears below half filling, where the system is a doped antiferromagnet. In this regime, the fermion excitations are nothing like those in a Fermi liquid, which carry both spin and charge. Rather, they split up into holons and spinons, carrying charge and spin separately. Moreover, the motion of a holon is believed to stir up the underlying antiferromagnetic order, leaving behind it a string of "wrong" spins. While direct observation of the holon string is difficult in electron systems, it has become possible in cold atom experiments due to recent experimental advances. Here, we point out the key feature of the holon strings, i.e. its Marshall phase, can be observed through measurements of spin correlations. Moreover, the interference of these strings leads to an anisotropic holon propagation clearly distinguishable than those of spinless fermions, as well as a large suppression of the magnetic order in the region swept through by the strings, as if the system is driven towards a spin liquid. We further illustrate the effect of the Marshall phase by showing the motion of a holon in the so-called $\sigma tJ$-model where the Marshall phase is removed.