Doping and disorder dependent isotope exponent in hole doped cuprates

Abstract

Abstract The nature of the variation of oxygen isotope exponent (IE) with the number of doped holes, p, in the CuO2 planes has been a source of considerable debate. The large IE over certain range of hole concentrations always casts a shadow over any proposal where non-phononic mechanism is invoked to describe pairing in cuprates. On the other hand, existing theoretical schemes, based on electron-phonon interactions, cannot describe the anomalous features shown by the IE as a function of hole concentration/disorder, either quantitatively or qualitatively. Based on an experiment relating the possibility of Fermi-surface reconstruction to the thermoelectric transport measurements (Laliberté et al. Nature Commun. 2, 432 (2011)), we propose here a simple scenario where isotope substitutions affect the charge/spin stripe state via the coupling to the underlying lattice and thereby change the superconducting Tc . In this picture, significant part of the IE, over an extended p-range, actually originates from the isotope induced stripe modulation and is not directly related to the characteristic energy scale of the phonons mediating the Cooper pairing. This proposal qualitatively explains all the disorder- and p-dependent features of the IE seen in hole doped high-Tc cuprates. We also provide with an outline of some experiments that can verify the degree of validity of the proposed scheme.