Explaining the Anomalous Isotope Shift in Cuprate High Temperature Superconductivity

The pairing mechanism of cuprate High Temperature Superconductors is still controversial. A vibrational component to the pairing mechanism is suggested by the anomalous Isotope Shift (IS), which is of order the BCS value at dopings well below the maximum Tc, but is very low at dopings close to the maximum Tc. Here, based on the Fluctuating Bond Model [1] (FBM), we re-examine the IS issue focusing on the oxygen soft mode associated in the FBM with the pseudogap - knowing that a soft mode plus a van Hove singularity in the electronic density of states is one mechanism capable of leading to the cuprate-type anomalous IS [2]. A quantum mechanical treatment of the FBM model in Born-Oppenheimer approximation shows soft excitations of a few meV. Solving the Eliashberg equation we evaluate the IS, and will present the results.

1) Jenhao Hsiao, Glenn J. Martyna and Dennis M. Newns, Phys. Rev. Lett. 114, 107001 (2015).
2) Dennis M. Newns, Glenn J. Martyna and Chang C. Tsuei, SPIN 07, 1750006 (2017).