Abstract
When a mobile hole is moving in an antiferromagnet it distorts the surrounding Néel order and forms a magnetic polaron. Such interplay between hole motion and antiferromagnetism is believed to be at the heart of high-temperature superconductivity in cuprates. In this article, we study a single hole described by the model with Ising interactions between the spins in two dimensions. This situation can be experimentally realized in quantum gas microscopes with Mott insulators of Rydberg-dressed bosons or fermions, or using polar molecules. We work at strong couplings, where hole hopping is much larger than couplings between the spins. In this regime we find strong theoretical evidence that magnetic polarons can be understood as bound states of two partons, a spinon and a holon carrying spin and charge quantum numbers, respectively. Starting from first principles, we introduce a microscopic parton description which is benchmarked by comparison with results from advanced numerical simulations. Using this parton theory, we predict a series of excited states that are invisible in the spectral function and correspond to rotational excitations of the spinon-holon pair. This is reminiscent of mesonic resonances observed in high-energy physics, which can be understood as rotating quark-antiquark pairs carrying orbital angular momentum. Moreover, we apply the strong-coupling parton theory to study far-from-equilibrium dynamics of magnetic polarons observable in current experiments with ultracold atoms. Our work supports earlier ideas that partons in a confining phase of matter represent a useful paradigm in condensed-matter physics and in the context of high-temperature superconductivity in particular. While direct observations of spinons and holons in real space are impossible in traditional solid-state experiments, quantum gas microscopes provide a new experimental toolbox. We show that, using this platform, direct observations of partons in and out of equilibrium are now possible. Extensions of our approach to the model are also discussed. Our predictions in this case are relevant to current experiments with quantum gas microscopes for ultracold atoms.
- Received 30 October 2017
- Revised 18 January 2018
DOI:https://doi.org/10.1103/PhysRevX.8.011046
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
At low temperatures, some materials become superconducting and support persistent electrical currents with zero resistance. The materials with the highest superconducting temperatures host some of the most exotic phases of matter, for which current theoretical understanding is limited. The carriers of charge in these materials emerge from holes inside a lattice, which is otherwise occupied by one electron per site, where the electron spins prefer to order themselves in a checkerboardlike pattern of alternating spin directions. To understand the dynamical properties of mobile holes, we introduce a theoretical formalism that highlights how these holes closely resemble pairs of quarks constituting mesons in high-energy physics.
We model the holes as being attached to one end of a string formed by displaced spins, with a fractional spin- excitation (a spinon) at its opposite end. For the case of Ising interactions favoring one spin direction, we show how this spinon acquires dynamics when the hole moves in loops. Similar to the situation in high-energy physics, we find that rotational excitations of the mesons (defined by the string and its attachments) exist. Utilizing the meson formalism, we calculate dynamics of holes that are far from equilibrium, which can be detected using state-of-the-art quantum gas microscopes. We show how such experiments can provide direct evidence of the meson nature of charge carriers in an antiferromagnetic spin environment.
Taking into account the effects of quantum fluctuations, our formalism might pave the way for simplified mean-field descriptions of high-temperature superconductors.
