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

We show theoretically that double photoemission (2e-ARPES) may be used to identify the pairing state in superconductors in which the Cooper pairs have a nonzero center-of-mass momentum, q_cm. We theoretically evaluate the 2e-ARPES counting rate, P⁽²⁾, for the cases of a d_x²−y² 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 2e-ARPES as an ideal tool for identifying and probing q_cm ≠ 0 superconducting pairing states in superconductors.