Comment on "Unified Formalism of Andreev Reflection at a Ferromagnet/Superconductor Interface" by T.Y. Chen, et al

TL;DR

This comment critiques Chen et al.'s claimed unified formalism for Andreev Reflection, demonstrating that their formulas are incorrect for non-zero spin polarization and violate fundamental physical principles.

Contribution

It clarifies that existing works already correctly address Andreev Reflection with arbitrary spin polarization, challenging Chen et al.'s claimed novelty.

Findings

Chen et al.'s formulas are incorrect for P ≠ 0

Their approach violates basic physical principles

Existing solutions already cover the problem

Abstract

A recent paper of Chen et al. claims to have derived an allegedly previously unavailable "unified" Andreev Reflection (AR) formalism for an arbitrary spin polarization P that recovers earlier results as its special limits. In this Comment we show that, contrary to this claim, there are numerous works correctly solving the problem formulated in this paper for an arbitrary P, while Chen et al formulas fail to correctly incorporate P \neq 0 effects and violate basic physical principles.