Energy spectrum of bound-spinons in the quantum Ising spin-chain ferromagnet

摘要

We study the excitation energy spectrum in the S = 1/2 ferromagnetic Ising spin chain with the easy axis z in a magnetic field h = {h(x), 0, h(z)}. According to Wu and McCoy's scenario of weak confinement, the fermionic spinon excitations (kinks), being free at h(z) = 0 in the ordered phase, are coupled into bosonic bound states at arbitrary small h(z) > 0. We calculate the energy spectrum of such excitations in the leading order in small hz, using different perturbative methods developed for the similar problem in the Ising Field Theory.