Observation of solitons in the S 1 2 antiferromagnetic chain [CuPM NO3 2 H2O 2]n by 13C NMR

We present 13C NMR investigations of the S 1 2 antiferromagnetically coupled Heisenberg chain system [CuPM NO3 2 H2O 2]n, PM C4N2H4 pyrimidine . For this material, as result of the Dzyaloshinskii Moriya interaction and an alternating g tensor, the ground state is characterized by a giant static spin canting and an anisotropic magnetic field induced spin excitation gap. We measured the spin lattice relaxation rate 1 T1 at three inequivalent carbon sites in the pyrimidine molecule as function of temperature. From these studies we deduce the magnetic excitation spectrum of copper pyrimidine dinitrate at a constant applied magnetic field of 9.3 T. The experimental data are discussed in context with recent ESR investigations, which have been interpreted in terms of breather, soliton and multi particle excitations based on the quantum sine Gordon field theor