Influence of multiorbitals and anisotropic Coulomb interactions on isotope effect coefficient in doped Fe-based superconductors

TL;DR

This paper presents a theoretical analysis of the isotope effect coefficient in doped Fe-based superconductors, revealing how it varies with hybridization, Coulomb interactions, and carrier density, and discussing implications for the superconductivity mechanism.

Contribution

It introduces a self-consistent Green's function approach to analyze isotope effects in a two-orbital model, highlighting the influence of multiorbital and anisotropic Coulomb interactions.

Findings

Isotope effect coefficient increases with hybridization.

It decreases with stronger Coulomb interactions.

Large isotope effect coefficients suggest phonons alone are insufficient for superconductivity.

Abstract

The present work describes the theoretical analysis of isotope effect coefficient as a function of transition temperature in two orbital per site model Hamiltonian in iron based superconducting system. The expression of isotope effect coefficient has been computed numerically and self-consistently by employing Green's function technique within the BCS-mean-field approximation. It is observed that the isotope effect coefficient increases with the increase of the hybridization while with the increase in Coulomb interaction it starts decreasing. On increasing the carrier density per site in two orbital per site iron pnictide system, isotope effect coefficient ($\alpha$) exhibits large values (much higher than BCS limit) at lower temperatures. While in the underdoped case, isotope effect coefficient shows minimum value in superconducting states of the iron based systems. Furthermore, it has been found that the large value of the isotope effect coefficient is the indication of the fact that the contribution of phonon alone is inadequate as the origin of superconductivity in these systems. Finally, the obtained theoretical results have been compared with experimental and existing theoretical observations in iron based superconductors.