Electron-phonon coupling induced pseudogap and the superconducting transition in Ba0.67K0.33BiO3 -: art. no. 180509

We study the single-particle density of states (DOS) across the superconducting transition (T-c = 31 K) in single-crystal Ba0.67K0.33BiO3 using ultrahigh resolution angle-integrated photoemission spectroscopy. The superconducting gap opens with a pileup in the DOS, Delta (5.3 K) = 5.2 meV and 2 Delta (0)/k(B)T(c) = 3.9. In addition, we observe a pseudogap below and above T-c occurring as a suppression in intensity over an energy scale up to the breathing mode phonon (similar to 70 meV). The results indicate electron-phonon coupling induces a pseudogap in Ba0.67K0.33BiO3.