Pairing Symmetry Studied from Impurity Effects in the Undoped Superconductor T'-La$_{1.8}$Eu$_{0.2}$CuO$_4$

TL;DR

This study investigates impurity effects in undoped T'-La$_{1.8}$Eu$_{0.2}$CuO$_4$ to determine its pairing symmetry, finding evidence that supports a $d$-wave superconducting gap mediated by spin fluctuations.

Contribution

It provides experimental evidence that the superconductivity in undoped T'-LECO has $d$-wave symmetry, similar to doped cuprates, based on impurity suppression rates.

Findings

Ni and Zn impurities suppress $T_c$ at similar rates.

Suppression rates are comparable to those in doped cuprates.

Results suggest $d$-wave pairing mediated by spin fluctuations.

Abstract

We have investigated the effects of magnetic Ni and nonmagnetic Zn impurities on the superconductivity in undoped T'-La$_{1.8}$Eu$_{0.2}$CuO$_4$ (T'-LECO) with the Nd$_2$CuO$_4$-type structure, using the polycrystalline bulk samples, to clarify the pairing symmetry. It has been found that both suppression rates of the superconducting transition temperature $T_\mathrm{c}$ by Ni and Zn impurities are nearly the same and are very similar to those in the optimally doped and overdoped regimes of hole-doped T-La$_{2-x}$Sr$_{x}$CuO$_4$ with the K$_2$NiF$_4$-type structure. These results strongly suggest that the superconductivity in undoped T'-LECO is of the $d$-wave symmetry and is mediated by the spin fluctuation.