Spin polarized carrier injection into high-T-c superconductors: A test forthe superconductivity mechanism

We point out in this short paper, that be it an s-wave or d-wave supercondu ctor, in a nonequilibrium situation (i.e., in the presence of excess unpola rized and polarized quasiparticles maintained by an injection current) the superconducting gap suppression by the presence of the same amount of exces s quasiparticles, can at best differ by a factor of 2, for a conventional B CS superconductor. For the high-T-c superconductors on the other hand, ther e is a huge difference in gap suppression between unpolarized and polarized quasiparticle injection, as observed in the experiments [V. A. Vasko eh al ., Phys. Rev. Lett. 78, 1134 (1997); T. A. Venkatesan et al., Appl. Phys. L ett. 71, 1718 (1997)]. We argue that this large anomaly has a natural expla nation within the interlayer tunneling mechanism of Wheatley, Hsu, and Ande rson [J. M. Wheatley, T. C. Hsu, and P. W. Anderson, Phys. Rev. B 37, 5897 (1988)], and is due to the excess polarized quasiparticles blocking the int erlayer pair tunneling process. We also point out that spin polarized quasi particle injection in a superconductor is a very easy way to distinguish be tween an s-wave or an anisotropic gap superconductor.