Effects of dilute nonmagnetic impurities on the Q=(pi,pi) spin-fluctuation spectrum in YBa2Cu3O7

TL;DR

This study investigates how dilute nonmagnetic impurities affect the spin-fluctuation spectrum at Q=(pi,pi) in YBa2Cu3O7 using the Hubbard model and RPA, revealing weak smearing effects and impurity scattering impacts.

Contribution

It provides a detailed theoretical analysis of impurity effects on spin fluctuations in high-Tc cuprates, incorporating impurity potential variations and comparing with experimental data.

Findings

Impurities cause weak smearing of the susceptibility spectrum.

Impurity scattering influences the frequency dependence of spin fluctuations.

Results align with experimental observations in Zn-doped YBa2Cu3O7.

Abstract

The effects of nonmagnetic impurities on the Q=(pi,pi) spin-fluctuation spectral weight Im chi(Q,omega) are studied within the framework of the two-dimensional Hubbard model using the random phase approximation. In the first part of the paper, the effects of the nonmagnetic impurities on the magnetic susceptibility of the noninteracting (U=0) system, chi_0(Q,omega), are calculated with the self-energy and the vertex corrections using various forms of the effective electron-impurity interaction. Here, the range and the strength of the impurity potential are varied as well as the concentration of the impurities. It is shown that the main effect of dilute impurities on chi_0(Q,omega) is to cause a weak smearing. In the second part, Im chi(Q,omega) is calculated for the interacting system. Here, the calculations are concentrated on the processes which involve the impurity scattering of the spin fluctuations with finite momentum transfers. In order to make comparisons with the experimental data on the frequency dependence of Im chi(Q,omega) in Zn substituted YBa2Cu3O7, results are given for various values of the model parameters.