Large copper isotope effect on the pseudogap in the high-temperature superconductor HoBa2Cu4O8D. Rubio Temprano, J. Mesot, S. Janssen, K. Conder, A. Furrer, A. Sokolov, V. Trounov, S. M. Kazakov, J. Karpinski and K. A. MüllerEur. Phys. J. B, 19 1 (2001) 5-8DOI: https://doi.org/10.1007/s100510170343