Spin polarized carrier injection into high-Tc superconductors:: A test for the superconductivity mechanism

We point out in this short paper, that be it an s-wave or d-wave superconductor, in a nonequilibrium situation (i.e., in the presence of excess unpolarized and polarized quasiparticles maintained by an injection current) the superconducting gap suppression by the presence of the same amount of excess quasiparticles, can at best differ by a factor of 2, for a conventional BCS superconductor. For the high-T-c superconductors on the other hand, there 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. Lett. 71, 1718 (1997)]. We argue that this large anomaly has a natural explanation within the interlayer tunneling mechanism of Wheatley, Hsu, and Anderson [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 interlayer pair tunneling process. We also point out that spin polarized quasiparticle injection in a superconductor is a very easy way to distinguish between an s-wave or an anisotropic gap superconductor.