Spin-Peierls transition in an incommensurately modulated system

Abstract

Under certain conditions uniform magnetic chains are known to be unstable for a lattice dimerization modulating the exchange integral, i.e. the spin-Peierls (SP) transition. In sufficiently high fields a SP system enters a magnetic discommensuration (MD) state incommensurate with the underlying lattice, characterized by the presence of midgap states.The question is raised, what happens in those magnetic systems that are not uniform from the beginning. Based on experimental evidence obtained in triclinic DMM-TCNQ2, it will be argued that in zero field there is an instability for a lattice modulation, that approaches the dimerization wave vector via a multiple of the original modulation vector. In sufficiently high fields the so created midgap band becomes magnetic field dependent, like the MD-phase of a regular SP-system.