  We have used neutron spectroscopy to investigate the spin dynamics of the
quantum (S = 1/2) antiferromagnetic Ising chains in RbCoCl3. The structure and
magnetic interactions in this material conspire to produce two magnetic phase
transitions at low temperatures, presenting an ideal opportunity for thermal
control of the chain environment. The high-resolution spectra we measure of
two-domain-wall excitations therefore characterize precisely both the continuum
response of isolated chains and the "Zeeman-ladder" bound states of chains in
three different effective staggered fields in one and the same material. We
apply an extended Matsubara formalism to obtain a quantitative description of
the entire dataset, Monte Carlo simulations to interpret the magnetic order,
and finite-temperature DMRG calculations to fit the spectral features of all
three phases.
