Unconventional isotope effects as evidence for polaron formation in cuprates A. Bussmann-Holder, H. Keller, A. R. Bishop, A. Simon, R. Micnas and K. A. Müller Europhys. Lett., 72 3 (2005) 423-429 Published online: 30 September 2005 DOI: 10.1209/epl/i2005-10252-6