# Angle-resolved photoemission spectroscopy of a Fermi-Hubbard system

## TL;DR

This paper develops ARPES for strongly interacting fermions in optical lattices, enabling the study of pseudogap phenomena and pairing mechanisms in quantum simulators, with benchmarking against quantum Monte Carlo calculations.

## Contribution

The authors adapt ARPES to optical lattice systems and demonstrate its effectiveness by measuring the spectral function of an attractive Fermi-Hubbard model, revealing pseudogap behavior.

## Key findings

- Evidence of a pseudogap above the superfluid transition temperature.
- Successful benchmarking of ARPES measurements with quantum Monte Carlo simulations.
- Potential application to doped repulsive Hubbard models.

## Abstract

Angle-resolved photoemission spectroscopy (ARPES) measures the single-particle excitations of a many-body quantum system with both energy and momentum resolution, providing detailed information about strongly interacting materials. ARPES is a direct probe of fermion pairing, and hence a natural technique to study the development of superconductivity in a variety of experimental systems ranging from high temperature superconductors to unitary Fermi gases. In these systems a remnant gap-like feature persists in the normal state, which is referred to as a pseudogap. A quantitative understanding of pseudogap regimes may elucidate details about the pairing mechanisms that lead to superconductivity, but developing this is difficult in real materials partly because the microscopic Hamiltonian is not known. Here we report on the development of ARPES to study strongly interacting fermions in an optical lattice using a quantum gas microscope. We benchmark the technique by measuring the occupied single-particle spectral function of an attractive Fermi-Hubbard system across the BCS-BEC crossover and comparing to quantum Monte Carlo calculations. We find evidence for a pseudogap in our system that opens well above the expected critical temperature for superfluidity. This technique may also be applied to the doped repulsive Hubbard model which is expected to exhibit a pseudogap at temperatures close to those achieved in recent experiments.