The Isotope Effect in Superconductors

TL;DR

This paper reviews the isotope effect in superconductors, focusing on factors beyond the pairing mechanism, including experimental and theoretical insights into how impurities, proximity, and non-adiabaticity influence the isotope coefficient.

Contribution

It provides a comprehensive review of the isotope effect in both conventional and high-$T_c$ superconductors, emphasizing non-mechanistic influences and experimental findings.

Findings

Magnetic impurities affect the isotope coefficient.

Proximity and non-adiabatic effects influence $T_c$ and penetration depth.

Experimental results for cuprate superconductors are discussed.

Abstract

We review some aspects of the isotope effect (IE) in superconductors. Our focus is on the influence of factors not related to the pairing mechanism. After summarizing the main results obtained for conventional superconductors, we review the effect of magnetic impurities, the proximity effect and non-adiabaticity on the value of the isotope coefficient (IC). We discuss the isotope effect of $T_c$ and of the penetration depth $\delta$. The theory is applied to conventional and high-$T_c$ superconductors. Experimental results obtained for YBa$_2$Cu$_3$O$_{7-\delta}$ related materials (Zn and Pr-substituted as well as oxygen-depleted systems) and for La$_{2-x}$Sr$_x$CuO$_4$ are discussed.