Isotopic Fingerprint of Electron-Phonon Coupling in High-TcCuprates

Abstract

Angle-resolved photoemission spectroscopy with low-energy tunable photons along the nodal direction of oxygen isotope substituted Bi(2)Sr(2)CaCu(2)O(8+delta) reveals a distinct oxygen isotope shift near the electron-boson coupling "kink" in the electronic dispersion. The magnitude (a few meV) and direction of the kink shift are as expected due to the measured isotopic shift of phonon frequency, and are also in agreement with theoretical expectations. This demonstrates the participation of the phonons as dominant players, as well as pinpointing the most relevant of the phonon branches.

Hard-Wired Dopant Networks and the Prediction of High Transition Temperatures in Ceramic Superconductors

“…Therefore it is gratifying that quasiparticle tunneling across a break junction perpendicular to the superconducting copper oxide planes showed 11 phonon features that match precisely with Raman spectra [53], decisively showing that HTSC is indeed caused by electron-phonon interactions along the c-axis, as previously argued from dynamical relaxation experiments [54]. Also the long-expected isotope effect at the phonon kink has been observed by ARPES [55]. The fact that all the c-axis phonon bands appear in the break junction experiment, and not just those associated with the O buckling mode in the CuO 2 plane [51], strongly supports the present model of zigzag percolative paths in a marginally stable all-atom network.…”

Correlation of the local and the macroscopic properties of high-temperature superconductors

“…Strong electron-phonon coupling was observed for both hole-and electron-doped HTSC compounds in neutron or X-ray scattering experiments and in tunneling spectra (see, for example, [4] and references therein). Recent high resolution angle-resolved photoemission (ARPES) measurements have found an oxygen isotope effect in the dispersion kink at the half-breathing phonon mode, hinting at an important role of oxygen vibrations inside the superconducting CuO 2 plane [5]. Since the above phonon modes are essentially local in their character, very important information may be extracted by the extended X-ray absorption fine structure (EXAFS) technique which is the most suitable for study of the local structure peculiarities.…”

“…The both classes have perovskite-like lattice with CuO n (n ¼ 4, 5,6) or Bi(Pb)O 6 complexes joined by the common oxygen ions. In bismuthates, the intersection of octahedral complexes in the three crystallographic directions determines their three-dimensional cubic structure.…”

Characteristics of oxygen isotope substitutions in the quasiparticle spectrum of Bi 2 Sr 2 CaCu 2 O 8+δ

“…Recent scanning tunneling microscope (STM) work has shown a shift in the 52 meV structure of about the expected amount for an oxygen mode [27], but this may be explained in terms of inelastic tunneling through a barrier [31][32][33]. Very recently new high precision low-energy ARPES data of Iwasawa et al [34] on a high quality single crystal of optimally doped Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) with a T c of 92 K have revealed a shift of the kink at 69 meV seen in the dispersion curves in the nodal direction for 16 O → 18 O substitution with little change in the spectrum outside the immediate kink region. By providing a more detailed analysis of the spectra in Ref.…”

“…By providing a more detailed analysis of the spectra in Ref. [34] we will show here that not only do these new measurements provide a fingerprint for the presence of a phonon contribution to the self energy of the charge carriers, but that they permit us to calculate the fraction of the bosonic coupling parameter λ associated with phonons and the fraction with magnetic excitations and conclude that the phonon contribution is ∼ 10% of the area under the spectral density. The major contribution to the glue is non phononic.…”