Destroying pairing by repulsion: the vortex-binding picture

When fermions interact via a repulsive dynamical interaction (which depends on the energy transfer), an s-wave superconductor can form. A hallmark of such pairing state are dynamical vortices in the gap function. However, when the repulsion becomes too strong, pairing is lost. We show that the corresponding quantum critical point (QCP) features an exotic singularitiy in the gap equation, which signals the binding of vortex-antivortex pairs at the transition. Furthermore, close to QCP the superconductor can be a mixed state of even-frequency and odd-frequency components and spontaneously break time-reversal symmetry.