Visualizing spinon Fermi surfaces with time-dependent spectroscopy

TL;DR

This paper proposes using time-dependent photo-emission spectroscopy in cold atom quantum simulators to visualize spinon Fermi surfaces and study their dynamics, revealing new insights into spin liquids and high-temperature superconductors.

Contribution

It introduces a novel application of time-dependent spectroscopy combined with magnetic field gradients to probe spinon excitations in quantum simulators, enabling visualization of unoccupied states and collective interactions.

Findings

Spinons can be driven to populate unoccupied states, revealing their band structure.

Spectral weight at specific momenta indicates collective spinon interactions.

Potential insights into Fermi arcs in cuprates are suggested.

Abstract

Quantum simulation experiments have started to explore regimes that are not accessible with exact numerical methods. In order to probe these systems and enable new physical insights, the need for measurement protocols arises that can bridge the gap to solid state experiments, and at the same time make optimal use of the capabilities of quantum simulation experiments. Here we propose applying time-dependent photo-emission spectroscopy, an established tool in solid state systems, in cold atom quantum simulators. Concretely, we suggest combining the method with large magnetic field gradients, unattainable in experiments on real materials, to drive Bloch oscillations of spinons, the emergent quasiparticles of spin liquids. We show in exact diagonalization simulations of the one-dimensional $t-J$ model that the spinons start to populate previously unoccupied states in an effective band structure, thus allowing to visualize states invisible in the equilibrium spectrum. The dependence of the spectral function on the time after the pump pulse reveals collective interactions among spinons. In numerical simulations of small two-dimensional systems, spectral weight appears at the ground state energy at momentum $\mathbf{q} = (\pi,\pi)$, where the equilibrium spectral response is strongly suppressed up to higher energies, indicating a possible route towards solving the mystery of the Fermi arcs in the cuprate materials.