Quantum spin chains with frustration due to Dzyaloshinskii-Moriya interactions

The properties of two quantum spin chain materials, K 2 CuSO 4 Cl 2 and K 2 CuSO 4 Br 2 , are studied by a variety of experimental techniques, including bulk measurements, neutron spectroscopy, and electron spin resonance. The hierarchy of relevant terms in the magnetic Hamiltonian is established. It is shown that these two compounds feature substantial Dzyaloshinskii-Moriya interactions that are uniform within each chain, but antiparallel in adjacent chains. The result is a peculiar type of frustration of interchain interactions, which leads to an unusual field-temperature phase diagram.