Bosonic Spectral Function in HTSC Cuprates: Part I - Experimental Evidence for Strong Electron-Phonon Interaction

In Part I we discuss accumulating experimental evidence related to the structure and origin of the bosonic spectral function \alpha ^{2}F in high-temperature superconducting (HTSC) cuprates near optimal doping. Some global properties of \alpha ^{2}F such as number and positions of peaks, are extracted by combining optics, neutron scattering, ARPES and tunnelling measurements. These methods give convincing evidence for strong electron-phonon interaction (EPI) with 1<\lambda \lesssim 3 in cuprates near optimal doping. Here we clarify how these results are in favor of the Eliashberg-like theory for HTSC cuprates near optimal doping.We argue that the neglect of EPI in some previous studies of HTSC was based on a number of deceptive prejudices related to the strength of EPI, on some physical misconceptions and misleading interpretation of experimental results.