Isotope effect on electron-phonon interaction in the multiband superconductor MgB2

We investigate the effect of isotope substitution on the electron-phonon interaction in the multiband superconductor MgB2 using tunable laser-based angle-resolved photoemission spectroscopy. The kink structure around 70 meV in the sigma band, which is caused by electron coupling to the E-2g phonon mode, is shifted to higher binding energy by similar to 3.5 meV in (MgB2)-B-10 and the shift is not affected by superconducting transition. These results serve as the benchmark for investigations of isotope effects in known, unconventional superconductors and newly discovered superconductors where the origin of pairing is unknown.