Size and mass of Cooper pairs determined by low-energy $\mu$SR and PNR
  The Pippard coherence length $\xi_0$ (the size of a Cooper pair) in an extreme type-I superconductor was determined directly through high-resolution measurement of the nonlocal electrodynamic effect combining low-energy muon spin rotation spectroscopy and polarized neutron reflectometry. The renormalization factor $Z$=m_cp*/2m (m_cp* and m are the mass of the Cooper pair and the electron, respectively) resulting from the electron-phonon interaction, and the temperature dependent London penetration depth $\lambda_L(T)$ were determined as well. A general expression linking $\xi_0$, $Z$ and $\lambda_L(0)$ is introduced and experimentally verified. This expression allows one to determine experimentally the Pippard coherence length in \textit{any} superconductor, independent of whether the electrodynamics is local or nonlocal, conventional or unconventional. 
V. Kozhevnikov, A. Suter, H. Fritzsche, V. Gladilin, A. Volodin, J.   Cuppens, T. Prokscha, E. Morenzoni, M. J. Van Bael, K....
cond-mat.supr-con