Interaction between impurities and solitons in quasi one-dimensional spin-Peierls systems

TL;DR

This paper investigates how impurities affect soliton behavior in spin-Peierls chains, revealing impurity-dependent soliton binding and interactions influenced by interchain elastic coupling.

Contribution

It provides a comparative analysis of impurity effects on solitons using various numerical methods and models lattice interactions quantum mechanically, classically, and with fixed dimerization.

Findings

Strong bonds form near spin-1/2 impurities, creating magneto-elastic solitons.

Solitons do not bind to spin-0 impurities but are weakly attracted to spin-1 impurities.

Interchain elastic coupling can confine solitons, leading to bound states or annihilation depending on impurity separation.

Abstract

The role of the spin-phonon coupling in spin-Peierls chains doped with spin-0 or spin-1 impurities is investigated by various numerical methods such as exact diagonalization, quantum Monte Carlo simulations and Density Matrix Renormalization Group. Various treatments of the lattice, in a fully quantum mechanical way, classically in the adiabatic approximation or using a fixed three-dimensional dimerization pattern are compared. For an isolated chain, strong bonds form between the two spin-1/2 sites next to the impurity site, leading to the appearance of magneto-elastic solitons. We also show that these excitations do not bind to spin-0 impurities but are weakly attracted by spin-1 impurities. However, the interchain elastic coupling generates an effective confining potential at the non-magnetic impurity site which can lead to the formation of soliton-impurity bound states. We also predict that a soliton and an antisoliton bound to two impurities on the same chain can annihilate each other when the separation between the impurities is smaller than a critical value depending on the interchain elastic constant.