Bose-Glass behaviour in Bi_{2}Sr_{2}Ca_{1-x}Y_{x}Cu_{2}O_{8} crystals   with columnar defects: experimental evidence for variable-range hopping
  We report on vortex transport in Bi_{2}Sr_{2}Ca_{1-x}Y_{x}Cu_{2}O_{8} crystals irradiated at different doses of heavy ions. We show evidence of a flux-creep resistivity typical of a variable-range vortex hopping mechanism as predicted by Nelson and Vinokur. 
J. C. Soret, L. Ammor, V. Ta Phuoc, R. De Sousa, A. Ruyter, A. Wahl,   G. Villard