Ni impurity induced enhancement of the pseudogap in cuprate high T_c superconductors

TL;DR

This study investigates how magnetic Ni and non-magnetic Zn impurities differently affect the pseudogap in cuprate superconductors, revealing that magnetic impurities enhance the pseudogap, challenging existing theories about its origin.

Contribution

It demonstrates that magnetic Ni impurities enhance the pseudogap, suggesting magnetic correlations are crucial, unlike non-magnetic Zn which suppresses it, providing new insights into the pseudogap's nature.

Findings

Ni enhances the pseudogap in cuprates.

Zn suppresses the pseudogap gradually.

Results challenge theories linking pseudogap to precursor superconductivity.

Abstract

The influence of magnetic Ni and non-magnetic Zn impurities on the normal state pseudogap (PG) in the c-axis optical conductivity of NdBa$_{2}$\{Cu$% _{1-y}$(Ni,Zn)$_{y}\}_{3}$O$_{7-\delta}$ crystals was studied by spectral ellipsometry. We find that these impurities which strongly suppress superconductivity have a profoundly different impact on the PG. Zn gives rise to a gradual and inhomogeneous PG suppression while Ni strongly enhances the PG. Our results challenge theories that relate the PG either to precursor superconductivity or to other phases with exotic order parameters, such as flux phase or d-density wave states, that should be suppressed by potential scattering. The apparent difference between magnetic and non-magnetic impurities instead points towards an important role of magnetic correlations in the PG state.