Effects of Nonmagnetic Impurity Doping on Spin Ladder System

TL;DR

This study investigates how nonmagnetic impurity doping affects the magnetic and thermodynamic properties of an antiferromagnetic spin-1/2 Heisenberg ladder system, revealing a crossover from localized impurity effects to a uniform power-law decay of correlations.

Contribution

It provides the first detailed quantum Monte Carlo analysis of impurity effects on spin ladders, highlighting a crossover in magnetic behavior at around 4% impurity concentration.

Findings

Localized spin-1/2 moments form around impurities

A crossover occurs at about 4% impurity concentration

Large Curie-like susceptibility observed at low temperatures

Abstract

Effects of nonmagnetic impurity doping on an AF spin-1/2 Heisenberg ladder system are studied by the QMC method. A single nonmagnetic impurity induces a localized spin-1/2 moment accompanied by "static" and enhanced AF correlations around it. Small and finite concentration of impurities induces a remarkable change of magnetic and thermodynamic properties with gapless excitations. It also shows rather sharp but continuous crossover around the concentration of about 4%. Above the crossover concentration, all the spins are strongly coupled participating in the enhanced and rather uniform power-law decay of the antiferromagnetic correlation. Below the crossover, each impurity forms an antiferromagnetic cluster only weakly coupled each other. For random distribution of impurities, large Curie-like susceptibility accompanied with small residual entropy is obtained at low temperatures in agreement with recent experimental observation in Zn-doped $SrCu_{2}O_{3}$. Temperature dependence of AF susceptibility shows power-law-like but weaker divergence than the single chain AFH in the temperature range studied.