Nonequilibrium Andreev resonances in ballistic graphene Andreev interferometers

We investigate the nonequilibrium populations of Andreev bound states (ABSs) in ballistic graphene three-terminal Josephson junctions (JJs). Our measurements reveal periodic resistance oscillations as a function of the superconducting phase, which is modulated by the applied magnetic flux. Additionally, we observe several voltage-induced crossovers, where resistance oscillations alternate between minima and maxima at integer flux quanta, corresponding to 0 and $\ensuremath{\pi}$ phase shifts, respectively. We utilize a microscopic model for long ballistic Andreev interferometers, accounting for both perturbative and nonperturbative scattering processes. This model attributes the $0\text{\ensuremath{-}}\ensuremath{\pi}$ crossovers to phase-sensitive Andreev reflections (ARs), which convert normal current into ABSs with nonequilibrium populations. Our combined theoretical and experimental approach suggests that unconventional energy-phase relations, such as $\ensuremath{\pi}$-shifted ABSs, can be created in multiterminal JJs without relying on complex Cooper quartet or Floquet physics.