Spin Meissner Effect in Superconductors and the Origin of the Meissner Effect

We propose a dynamical explanation of the Meissner effect in superconductors and predict the existence of a spin Meissner effect: that a macroscopic spin current flows within a London penetration depth $\lambda_L$ of the surface of superconductors in the absence of applied external fields, with carrier density = the superfluid density and carrier speed $v=\hbar/(4m_e\lambda_L$) ($m_e=$bare electron mass). The two members of a Cooper pair circulate in orbits of radius $2\lambda_L$ in opposite direction and the spin current in a Cooper pair has orbital angular momentum $\hbar$. Our description also provides a 'geometric' interpretation of the difference between type I and type II superconductors.