Abstract
Surprising properties of doped Mott insulators are at the heart of many quantum materials, including transition metal oxides and organic materials. The key to unraveling complex phenomena observed in these systems lies in understanding the interplay of spin and charge degrees of freedom. One of the most debated questions concerns the nature of charge carriers in a background of fluctuating spins. To shed new light on this problem, we suggest a simplified model with mixed dimensionality, where holes move through a Mott insulator unidirectionally while spin exchange interactions are two dimensional. By studying individual holes in this system, we find direct evidence for the formation of mesonic bound states of holons and spinons, connected by a string of displaced spins – a precursor of the spin-charge separation obtained in the 1D limit of the model. Our predictions can be tested using ultracold atoms in a quantum gas microscope, allowing to directly image spinons and holons, and reveal the short-range hidden string order which we predict in this model.
Highlights
The Fermi-Hubbard model represents one of the most fundamental and paradigmatic models of strongly correlated matter
Instead of the two-dimensional (2D) t − J model, which is commonly used to capture the interplay of spin and charge degrees of freedom in the low energy sector of the Hubbard model [3], we suggest to realize a system with mixed dimensionality: While the spin system is fully 2D, the holes doped into the system can only move along one direction, see Fig. 1 (a)
Even in the presence of quantum fluctuations of the surrounding spins, we demonstrate that the individual partons can be directly detected using experimatal tools available in systems of ultracold atoms in quantum gas microscopes [27,28,29,30,31]
Summary
The Fermi-Hubbard model represents one of the most fundamental and paradigmatic models of strongly correlated matter. These authors suggested that the single hole can be understood as a bound state of two partons: a neutral spinon and a spin-less holon This closely resembles mesons formed by quark-antiquark pairs in high-energy physics. We study the resulting mixD t − J model in the low-doping regime and demonstrate that holes form mesonic bound states of spinons and holons (b), which can be directly observed using quantum gas microscopes. In a genuine 1D system, hole excitations decay into pairs of deconfined spinons and holons [32,33,34] This fractionalization of the hole introduces quasi-long range non-local string order in the 1D system [35], which has recently been observed using a Fermi gas microscope [36]. We discuss the possibilities of stripe formation and pairing of holes in the mixD model
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