Impurity Effect on Spin Ladder System

TL;DR

This study investigates how nonmagnetic impurities affect the magnetic properties of a spin ladder system, revealing that small impurity levels can close the spin gap and induce a quantum phase transition, aligning with experimental observations.

Contribution

It provides a theoretical explanation for impurity-induced gap closing in spin ladders, highlighting the role of low-energy states and proposing a quantum phase transition scenario.

Findings

Impurities enhance low-energy states and magnetic susceptibilities.

Small doping levels can eliminate the spin gap.

Results align with experimental data on Zn-doped SrCu₂O₃.

Abstract

Effects of nonmagnetic impurity doping in a spin ladder system with a spin gap are investigated by the exact diagonalization as well as by the variational Monte Carlo calculations. Substantial changes in macroscopic properties such as enhancements in spin correlations and magnetic susceptibilities are observed in the low impurity concentration region, which are caused by the increase of low-energy states. These results suggest that small but finite amount of nonmagnetic impurity doping relevantly causes the reduction or the vanishment of the spin gap. This qualitatively explains the experimental result of Zn-doped SrCu$_{2}$O$_{3}$ where small doping induces gapless nature. We propose a possible scenario for this drastic change as a quantum phase transition in a spin gapped ladder system due to spinon doping effects.