Pair Breaking Caused by Magnetic Impurities in the High-T$_\text{C}$ Superconductor Bi$_{2.1}$Sr$_{1.9}$Ca(Cu$_{1-x}$Fe$_{x}$)$_{2}$O$_{y}$

TL;DR

This study investigates how magnetic impurities like Fe affect superconductivity in cuprates, revealing that they mainly reduce pair lifetime and T_C without altering the pairing strength.

Contribution

It introduces the use of Tomographic Density of States to show magnetic impurities suppress T_C by increasing pair-breaking rate without changing the superconducting gap.

Findings

Superconducting gap remains unchanged with Fe doping.

T_C decreases as pair-breaking rate increases.

Magnetic impurities primarily affect pair lifetime, not pairing strength.

Abstract

Conventional superconductivity is robust against the addition of impurities unless the impurities are magnetic in which case superconductivity is quickly suppressed. Here we present a study of the cuprate superconductor Bi$_2$Sr$_2$Ca$_1$Cu$_2$O$_{8+\delta}$ that is intentionally doped with the magnetic impurity, Fe. Through the use of our Tomographic Density of States (TDoS) technique, we find that while the superconducting gap magnitude is essentially unaffected by the inclusion of iron, the onset of superconductivity, T$_{C}$, and the pair-breaking rate are strongly dependent and correlated. These findings suggest that, in the cuprates, the pair-breaking rate is critical to the determination of T$_{C}$ and that magnetic impurities do not disrupt the strength of pairing but rather the lifetime of the pairs.