Suppression of Nonequilibrium Quasiparticle Transport in Flat-Band Superconductors

We study nonequilibrium transport through a superconducting flat-band lattice in a two-terminal setup with the Schwinger-Keldysh method. We find that quasiparticle transport is suppressed and coherent pair transport dominates. For superconducting leads, the ac supercurrent overcomes the dc current, which relies on multiple Andreev reflections. With normal-normal and normal-superconducting leads, the Andreev reflection and normal currents vanish. Flat-band superconductivity is, thus, promising not only for high critical temperatures, but also for suppressing unwanted quasiparticle processes.