Impurity effects on electron-mode coupling in high-temperature superconductors

Despite years of intensive research on copper oxide superconductors with high transition temperatures (T-c), the driving force of superconductivity has not yet been clarified. Angle-resolved photoemission spectroscopy (ARPES)(1-3) measurements have uncovered an important contribution of lattice vibrations (phonons) to superconductivity, sparking a fierce debate on the nature of the 'glue'-phonons or magnetic excitations-binding together the superconducting Cooper pairs(1-11). However, it is difficult to distinguish these two pairing forces owing to their similar energy scales. Here, we propose a fresh approach to investigate the origin of many-body interactions in these superconductors: an impurity-substitution effect on the low-energy dynamics, which is a magnetic analogue of the isotope effect used for classical superconductors. Our ARPES results reveal that the impurity-induced changes in the electron self-energy show a good correspondence to those of magnetic excitations(12-18), indicating the importance of spin fluctuations to electron pairing in the high-T-c superconductors.