One-dimensional (1D) systems exhibit a range of unusual and interesting phenomena, and the challenge for scientists is to understand the underlying physics that causes them. An international team of researchers has used high-resolution inelastic neutron scattering on the time-of-flight spectrometer LET to investigate bis-piperidinium copper tetrachloride (BPCC), a quantum spin-ladder material which consists of two coupled spin-½ chains. They were able to measure two kinds of novel magnetic excitation, bound states at zero field and fully field-polarized Haldane modes. They further demonstrated that the magnetic response in BPCC can be explained accurately by state-of-the-art numerical (DMRG and series-expansion) methods. Their work provides a systematic understanding of the magnetic excitations in a broad family of gapped 1D quantum magnets, including ladder, alternating-chain, and Haldane systems.
Related publication: S. Ward et al. “Bound States and Field-Polarized Haldane Modes in a Quantum Spin Ladder" Phys. Rev. Lett. 118(2017), 177202, DOI: 10.1103/PhysRevLett.118.177202