Spectroscopy of Quasiparticle Excitations in Fermi-Hubbard Systems

Itinerant spin polarons, bound states of a dopant and a spin-flip, even in the absence of superexchange interactions, have been theoretically predicted in geometrically frustrated lattices. We directly image itinerant spin polarons in a triangular lattice Fermi-Hubbard system realised with ultracold Lithium-6 atoms [1]. Using full spin-charge resolution, we are able to measure arbitrary n-point correlation functions for a range of dopings and interaction strengths. We also present preliminary work towards characterization of systems of strongly interacting lattice fermions with Raman spectroscopy. This powerful approach can characterize excitations with energy and momentum resolution, allowing for measurement of the full many-body spectral function. As a first step, we benchmark this technique in the square lattice, where we directly inject magnon excitations and measure their binding energy. This scheme is applicable to general lattice geometries, and the application to frustrated lattices (such as the triangular) should allow spectroscopic characterization of the itinerant spin polarons present in this setting [2].

[1] arXiv:2308.12951

[2] arXiv:2312.00768