Anomalous Hopping Exponents of Ultrathin Films of Metals
  The temperature dependence of the resistance R(T) of ultrathin quench-condensed films of Ag, Bi, Pb and Pd has been investigated. In the most resistive films, R(T)=Roexp(To/T)^x, where x=0.75. Surprisingly, the exponent x was found to be constant for a wide range of Ro and To in all four materials, possibly implying a consistent underlying conduction mechanism. The results are discussed in terms of several different models of hopping conduction. 
N. Markovic, C. Christiansen, D. E. Grupp, A. M. Mack, G.   Martinez-Arizala, and A. M. Goldman