Distinguishing finite momentum superconducting pairing states with two-electron photoemission spectroscopy

Abstract: We show theoretically that double photoemission (2$e$-ARPES) may be used to identify the pairing state in superconductors in which the Cooper pairs have a nonzero center-of-mass momentum, ${\bf q}{cm}$. We theoretically evaluate the 2$e$ ARPES counting rate, $P^{(2)}$, for the cases of a $d{x^2-y^2}$-wave superconductor, a pair-density-wave (PDW) phase, and a Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) phase. We show that $P^{(2)}$ provides direct insight into the center-of-mass momentum and spin state of the superconducting condensate, and thus can distinguish between these three different superconducting pairing states. In addition, $P^{(2)}$ can be used to map out the momentum dependence of the superconducting order parameter. Our results identify 2$e$-ARPES as an ideal tool for identifying and probing ${\bf q}_{cm} \neq 0$ superconducting pairing states in superconductors.