Indication of unconventional superconductivity in layered bismuth chalcogenide superconductor LaO0.6F0.4Bi(S,Se)2 revealed by Se isotope effect

TL;DR

This study investigates the Se isotope effect in LaO0.6F0.4Bi(S,Se)2 superconductors and finds no change in critical temperature, indicating unconventional pairing mechanisms beyond phonon mediation.

Contribution

It provides experimental evidence suggesting that superconductivity in layered bismuth chalcogenides is likely unconventional, challenging phonon-mediated pairing theories.

Findings

No Tc change with Se isotope substitution

Suggests non-phonon pairing mechanism

Indicates possible unconventional superconductivity

Abstract

We have investigated the Se isotope effect in layered bismuth chalcogenide (BiCh2-based) superconductor LaO0.6F0.4Bi(S,Se)2 with 76Se and 80Se. For all examined samples, the Se concentration, which is linked to the superconducting properties, is successfully controlled within x = 1.09-1.14 in LaO0.6F0.4BiS2-xSex. From the magnetization and electrical resistivity measurements, changes in Tc are not observed for the LaO0.6F0.4Bi(S,Se)2 samples with 76Se and 80Se isotopes. Our results suggest that pairing in the BiCh2-based superconductors is not mediated by phonons, and unconventional superconductivity states may emerge in the BiCh2 layers of LaO0.6F0.4Bi(S,Se)2.