Interplay of electron–lattice interactions and superconductivity in Bi2Sr2CaCu2O8+δ

Abstract

Formation of electron pairs is essential to superconductivity. For conventional superconductors, tunnelling spectroscopy has established that pairing is mediated by bosonic modes (phonons); a peak in the second derivative of tunnel current d2I/dV2 corresponds to each phonon mode. For high-transition-temperature (high-T(c)) superconductivity, however, no boson mediating electron pairing has been identified. One explanation could be that electron pair formation and related electron-boson interactions are heterogeneous at the atomic scale and therefore challenging to characterize. However, with the latest advances in d2I/dV2 spectroscopy using scanning tunnelling microscopy, it has become possible to study bosonic modes directly at the atomic scale. Here we report d2I/dV2 imaging studies of the high-T(c) superconductor Bi2Sr2CaCu2O8+delta. We find intense disorder of electron-boson interaction energies at the nanometre scale, along with the expected modulations in d2I/dV2 (refs 9, 10). Changing the density of holes has minimal effects on both the average mode energies and the modulations, indicating that the bosonic modes are unrelated to electronic or magnetic structure. Instead, the modes appear to be local lattice vibrations, as substitution of 18O for 16O throughout the material reduces the average mode energy by approximately 6 per cent--the expected effect of this isotope substitution on lattice vibration frequencies. Significantly, the mode energies are always spatially anticorrelated with the superconducting pairing-gap energies, suggesting an interplay between these lattice vibration modes and the superconductivity.

Strong-coupling analysis of scanning tunneling spectra in Bi2Sr2Ca2CuBerthod1, Fasano2, Maggio-Aprile3 et al. 2013Phys. Rev. B

“…7), similar to the values observed in Bi-2212. 78 This feature therefore does not provide a good estimate of s . This difference with classical superconductors is a consequence of the d-wave symmetry of the gap.…”

Determinant quantum Monte Carlo study of the two-dimensional single-band Hubbard-Holstein model

“…Although the identity of this mode (be it an electronic collective mode or one or more phonon modes) remains controversial, the appearance of the dispersion renormalizations at multiple energy scales ranging from 10 -110 meV strongly suggests coupling to a spectrum of oxygen phonons. [18][19][20][21][22][23] These electronic renormalizations have analogous features in the density of states as probed by scanning tunnelling microscopy [24][25][26][27][28][29][30][31] as well as in the optical properties of the cuprates. 32,33 Moving beyond the cuprates, strong e-ph and electronelectron (e-e ) interactions also are believed to be operative in a number of other systems.…”

Strong pressure-dependent electron-phonon coupling in FeSe

“…The role of lattice vibrations in the mechanism of SC in unconventional superconductors is still controversial. The observation of strong electron-phonon and spin-phonon coupling, both in cuprates [32][33][34][35] and iron superconductors [36][37][38][39][40][41] indicates that the electron-phonon coupling (EPC) may play an important role in the unconventional superconductors, at least to explain the observed Fe-isotope effect [42], the anomalous temperature dependence of the local Fe-As displacement [43], gap anisotropy, and the correlation of T c with the Fe-anion height [44]. These observations also suggest polaron and/or bipolaron driven superconductivity in this material [45][46][47][48][49][50].…”