Theory of SIS tunnelling in cuprates.pdf

a r X i v : c o n d - m a t / 0 1 0 2 2 8 4 v 3 [ c o n d - m a t .s u p r - c o n ] 2 3 F e b 2 0 0 1 Theory of SIS tunnelling in cuprates A.S. Alexandrov and C. Sricheewin Department of Physics, Loughborough University, Loughborough LE11 3TU, U.K. Abstract We show that the single-particle polaron Green’s function describes SIS tun- nelling in cuprates, including the absence of Ohm’s law at high voltages, the dip/hump features in the first derivative of the current, a substantial inco- herent spectral weight beyond quasiparticle peaks and unusual shape of the peaks. The theory allows us to determine the characteristic phonon frequen- cies, normal and superconducting gaps, impurity scattering rate, and the electron-phonon coupling from the tunnelling data. PACS numbers:74.20.Mn,74.20.-z,74.25.Jb Typeset using REVTEX 1 There is a number of anomalous properties of high-Tc cuprates, which seem to be intrinsic and universal. The isotope effect on the carrier mass [1], unusually high values of the static dielectric constants [2], and the non-Fermi liquid and non-BCS spectral densities observed in the angle-resolved photoemission (ARPES) [3–5], superconductor- insulator- normal metal (SIN) and superconductor- insulator-superconductor(SIS) tunnelling spectra [6–12] are among those. The isotope effect and the high values of the static dielectric constants as well as the optical spectroscopy [13] suggest that electron-phonon interaction is more than sufficient to bind carriers and phonons into small polarons and bipolarons in highly polarisable cuprates [2,14]. The bipolaron theory [15] provides a natural explanation of the normal state pseudogap (as a half of the bipolaron binding energy, ?p) [16,17], NMR linewidth [16], normal state kinetics [15], SIN tunnelling [18] and ARPES [19,20]. The theory accounts for two distinct energy gaps (coherent and incoherent) [21] as observed in the recent tunnelling [10–12] and Andreev reflection experiments [22,10], for the param