Observation of Magnon-Polarons in the Fermi-Hubbard Model

TL;DR

This paper reports the experimental observation of magnon-polarons in a doped Fermi-Hubbard system, revealing how magnetic excitations interact with charge carriers and are renormalized, advancing understanding of strongly correlated electron systems.

Contribution

It introduces the first observation of magnon-polarons in a cold atom Fermi-Hubbard system, demonstrating the dressing of magnons by doped holes using Raman spectroscopy.

Findings

Detection of magnon-polaron formation with doping

Energy shift of polarons depends on momentum

Spectral weight reduction with increased doping

Abstract

The interplay of magnetic excitations and itinerant charge carriers is a ubiquitous phenomenon in strongly correlated electron systems. In the vicinity of magnetically ordered phases, strong interactions between itinerant quasiparticles and magnetic excitations can result in the dramatic renormalization of both. A key theoretical question is understanding the renormalization of the magnon quasiparticle, a collective spin excitation, upon doping a magnetic insulator. Here, we report the observation of a new type of quasiparticle arising from the dressing of a magnon with the doped holes of a cold atom Fermi-Hubbard system, i.e. a magnon-Fermi-polaron. Utilizing Raman excitation with controlled momentum in a doped, spin-polarized band insulator, we address the spectroscopic properties of the magnon-polaron. In an undoped system with strong interactions, photoexcitation produces magnons, whose properties are accurately described by spin wave theory. We measure the evolution of the photoexcitation spectra as we move away from this limit to produce magnon-polarons due to dressing of the magnons by charge excitations. We observe a shift in the polaron energy with doping that is strongly dependent on the injected momentum, accompanied by a reduction of spectral weight in the probed energy window. We anticipate that the technique introduced here, which is the analog of inelastic neutron scattering, will provide atomic quantum simulators access to the dynamics of a wide variety of excitations in strongly correlated phases.