One-dimensional physics of the frustrated quantum magnet PHCC

Abstract We report a comprehensive microscopic study of the frustrated quantum magnet PHCC, (C 4 H 12 N 2 )Cu 2 Cl 6 , using density-functional band-structure calculations combined with numerical quantum many-body simulations of the underlying spin Hamiltonian. We show that the magnetism of PHCC is captured by a one-dimensional model of the frustrated spin chain with alternating nearest-neighbor couplings ( J 1 = 23.1 K, J 1 ′ = 7.0 ${J}_{1}^{\prime }=7.0$ K) and uniform next-nearest-neighbor couplings ( J 2 = 13.9 K). This model, which can also be thought of as a zigzag ladder, provides a quantitative description of the magnetic susceptibility and the magnetization process and accounts for the observed dispersion of the single-triplet band and its merging into a continuum near the Brillouin zone center. We also make predictions for the existence of sharp bound (antibound) states of two triplets, below (above) the bottom (upper) edge of the two-particle scattering continuum.