Visualizing spinon Fermi surfaces with time-dependent spectroscopy

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.