ИСТИНА

THz phonon spectroscopy studies of bismuth cuprates are overviewed. Facts are presented evidencing a strong electron–phonon interaction in doped BSCCO superconductors. A pronounced fine structure in dI/dV- characteristics of Josephson break junctions in Bi-2212 and Bi-2223 has been observed which is caused by a nonlinear interaction of АС Josephson current with Raman-active optical phonon modes. For Bi-2223 the range of frequencies extended up to 25 THz, including the apex oxygen mode OSr with the energy close to 80 meV and two-phonon resonances (OSr + Bi), (OSr + Sr) and (OSr + Cu). At the same time no traces of the magnetic resonance were observed, which allows to conclude that the magnetic resonance doesn't participate in the formation of superconducting properties of bismuth cuprates. The observed “quantization” of the “gap” voltage Vgn = n(2 /e) for natural nanosteps on the cryogenically cleaved surfaces of Bi-2212 and Bi-2223 (j || c) proves the existence of the intrinsic Josephson effect (n is the number of contacts in a nanostep). A sharp extra structure in the current-voltage characteristics (CVC’s) of nanosteps is attributed to the presence of the extended van Hove singularity (EVHS) close to the Fermi level in slightly overdoped and slightly underdoped samples. A superconducting gap in bismuth cuprates is found to scale with Tc on doping. An observed giant instability in I(V) – characteristics of Bi- 2212 and Bi-2223 (j || c) nanosteps is probably caused by a resonant emission of 2 – optical phonons in a process of recombination of nonequilibrium quasiparticles (Krasnov - Schnyder model).