Retention of Two-Band Superconductivity in Highly Carbon-Doped MgB2

TL;DR

This study investigates how high levels of carbon doping affect two-band superconductivity in MgB2, revealing that two-band behavior persists due to selective suppression of interband scattering despite increased disorder.

Contribution

It demonstrates that two-band superconductivity is retained in highly carbon-doped MgB2 due to selective suppression of interband scattering, challenging dirty-limit expectations.

Findings

Energy gap of pi-bands reduced by half in doped samples

Two-band superconductivity persists despite high doping levels

Selective suppression of interband scattering maintains two-band behavior

Abstract

Tunneling data on MgB_{1.8}C_{0.2} show a reduction in the energy gap of the pi-bands by a factor of two from undoped MgB2 that is consistent with the Tc reduction, but inconsistent with the expectations of the dirty limit. Dirty-limit theory for undoped MgB2 predicts a single gap about three times larger than measured and a reduced Tc comparable to that measured. Our heavily-doped samples exhibit a uniform dispersion of C suggestive of significantly enhanced scattering, and we conclude that the retention of two-band superconductivity in these samples is caused by a selective suppression of interband scattering.