Low-energy excitations of spin-Peierls chains with modified bond-impurities

TL;DR

This paper studies how modified bond-impurities in spin-Peierls chains create new low-energy excitations, including bound states of solitons and localized spins, even in isolated chains, advancing understanding of impurity effects in quantum spin systems.

Contribution

It introduces a model analyzing the effects of bond-defects in spin-Peierls systems, revealing the formation of bound states and low-energy excitations due to impurities.

Findings

Modified bonds induce new low-energy excitations below the spin gap.

Bound states of solitons and localized spins are formed at impurity sites.

Confining potential exists even in isolated chains.

Abstract

The introduction of modified bond-defects in spin-Peierls systems is investigated in a model of antiferromagnetic Heisenberg spin chains coupled to adiabatic phonons. Generically, new low-energy magnetic or non-magnetic excitations appear below the bulk spin gap energy. When two adjacent bonds are modified, these excitations can be interpreted in terms of boundstates of a soliton with the localized spin-1/2 located on the impurity site. It is shown that the confining potential occurs even in the case of {\it isolated} chains.