Large copper isotope effect on the pseudogap in the high-temperature superconductor HoBa2Cu4O8 D. Rubio Temprano, J. Mesot, S. Janssen, K. Conder, A. Furrer, A. Sokolov, V. Trounov, S. M. Kazakov, J. Karpinski and K. A. Müller Eur. Phys. J. B, 19 1 (2001) 5-8 Published online: 15 January 2001 DOI: 10.1007/s100510170343