According to Abrikosov [1] а high transition temperature T_c in HTSC occurs because of the presence near the Fermi level of an extended van Hove singularity. Due to Abrikosov's model optical phonons with small wave vectors play a leading role in pairing. A strong electron-phonon coupling in HTSC was confirmed by studies of the effect of generation of Raman-active optical phonons by АС Josephson current [2, 3], by photoemission spectroscopy data [4], by studies of the isotop effect [5], and the effect of renormalization of the quasi-particle density of states at temperatures below Т_с [6]. In the present investigation an interaction between the АС Josephson current and Raman-active phonon modes in the entire range of phonon frequencies (up to 20 THz) was observed in doped Bi-2212 single crystals. It has been found that in the current-voltage characteristics of doped Bi-2212 Josephson junctions the structure related to generation of optical phonon modes can be observed in both underdoped аnd overdoped single crystals, with the doping level having only а negligible effect on the frequency of the main phonon modes. This means that the electron-phonon coupling in BSCCO does not change significantly over the entire region where superconductivity exists. At the same time we have not observed any structure which could be related to the "magnetic resonance" mode whose energy is expected to change significantly on doping. Thus the role of magnon modes in pairing is questionable.
References
1. А.А. Abrikosov, Physica С 341-348, 97 (2000).
2. Ya.G. Ponomarev et al., Solid State Commun. 111, 513 (1999).
3. Е.G. Maksimov et al., Solid State Commun. 111, 391 (1999).
4. А. Lanzara et al., Nature 412, 510 (2001).
5. G.М. Zhao et al., Nature 385, 236 (1997).
6. D. Shimada et al., Physica С 298, 195 (1998).

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1. Extended van Hove Singularity, Strong Electron-Phonon Interaction and Superconducting Gap in Doped Bi-2212 Single Crystals 
2. Scaling of superconducting gap and critical temperature in doped Bi-2212, Bi-2201 and Hg-1201