Experimental Evidence for Zero DC Resistance of Superconductors
  Even after nearly a century of discovery of superconductivity, there has been no direct experimental proof of the expected zero resistance of superconductors. Indeed, it has been believed that it is impossible to experimentally show that the resistance has fallen exactly to zero. In this work we demonstrate that the dc resistivity of a superconducting material below the transition temperature has to be exactly zero. 
S. Sarangi, S. P. Chockalingam, Raghav G. Mavinkurve and S. V. Bhat