Quantum destruction of stiffness in diluted antiferromagnets and superconductors

TL;DR

This paper investigates how quantum effects can destroy the stiffness of long-range order in diluted 2D antiferromagnets and superconductors, explaining experimental neutron scattering data and revealing a sharp transition between ordered phases.

Contribution

It introduces simplified models showing quantum destruction of stiffness at the percolation threshold, extending understanding of disordered quantum magnetic and superconducting systems.

Findings

Long-range order can persist at the percolation threshold despite disorder.

Quantum effects can dramatically alter the stiffness of order.

A sharp transition between stiff and floppy phases is identified.

Abstract

The reduction of 2D superconducting or antiferromagnetic order by random dilution is studied as a model for the 2D diluted Heisenberg antiferromagnet (DHAF) La$_2$Cu$_{1-p}$(Zn,Mg)$_p$O$_4$ and randomly inhomogeneous 2D suerconductors. We show in simplified models that long-range order can persist at the percolation threshold despite the presence of disordered one-dimensional segments, contrary to the classical case. When long-range order persists to the percolation threshold, charging effects (in the superconductor) or frustrating interactions (in the antiferromagnet) can dramatically modify the stiffness of the order. This quantum destruction of stiffness is used to model neutron scattering data on La$_2$Cu$_{1-p}$(Zn,Mg)$_p$O$_4$. In a certain simplified model, there is a sharp stiffness transition between ``stiff'' and ``floppy'' ordered phases.