We study the magnetic excitation spectrum of the spin-1 chain with Hamiltonian <Emphasis FontCategory="NonProportional">H=Σ<Subscript> i </Subscript> cos θ <Emphasis Type="Bold">S <Subscript> i </Subscript> · <Emphasis Type="Bold">S <Subscript> i+1</Subscript> + sin θ(<Emphasis Type="Bold">S <Subscript> i </Subscript> · <Emphasis Type="Bold">S <Subscript> i+1</Subscript>)<Superscript>2</Superscript>. We focus on the range 0 ≤ θ ≤ + π/4 where the spin chain is in the gapped Haldane phase. The excitation spectrum and static structure factor is studied...</superscript></subscript></emphasis></subscript></emphasis></subscript></emphasis></subscript></emphasis></subscript></emphasis>

We develop a non-perturbative local moment approach (LMA) for the gapped Anderson impurity model (GAIM), in which a locally correlated orbital is coupled to a host with a gapped density of states. Two distinct phases arise, separated by a level-crossing quantum phase transition: a screened...