Andreev reflection in normal metal/charge- 4e superconductor junctions

We investigate the Andreev reflection in a normal metal/charge-4e superconductor junction.Compare with the electron-hole conversion in normal charge-2e superconductors, here four electrons participate simultaneously, enriching the possibility of conversion ways.Using nonequilibrium Green's function method, we obtain a four-particle-type Laudauer-B\"uttiker formula with generalized charge-4e anomalous Green's function to describe it.We then calculate and clarify the behavior of the Andreev coefficient with various incident energy and show the conductance contributed by it.Our research makes up the blank of research for transport property of charge-4e superconductors and can be served as hallmarks for future experimental verifications.