Order from Disorder: Non Magnetic Impurities in the Spin-gap Phase of the Cuprates

TL;DR

This paper investigates the effects of non-magnetic impurities in the spin-gap phase of cuprates using a mean-field approach, revealing a specific density of states and quasi long-range order at zero temperature.

Contribution

It provides an exact evaluation of the density of states in the presence of impurities and predicts specific decay of spin correlations and enhanced low-energy fluctuations.

Findings

Density of states proportional to 1/(f(f|f|/D))

Quasi long-range order at T=0 with correlations decreasing as n_i/ln^2(n_i R_{ij})

Enhanced low energy fluctuations in neutron scattering

Abstract

We solve the problem of $N$ non magnetic impurities in the staggered flux phase of the Heisenberg model which we assume to be a good mean-field approximation for the spin-gap phase of the cuprates. The density of states is evaluated exactly in the unitary limit and is porportional to $1/\left (\omega \ln^2(|\omega|/D))$, in analogy with the 1D case of doped spin-Peierls and two-leg ladders compounds. We argue that the system exhibits a quasi long-range order at T=0 with instantaneous spin-spin correlations decreasing as $n_i/ \ln^2\left (n_i R_{ij})$ for large distances $R_{ij}$ and we predict enhanced low energy fluctuations in Neutron Scattering.