Linking dynamics and kinetics of defect-doped spin chains and ladders

• Applicants: Professor Dr. Bernd Büchner; Professor Dr. Christian Hemker-Heß
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2013 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 245897470

The goal of the present DACH Swiss-German proposal is to experimentally investigate the correlation between dynamical and transport properties of one dimensional quantum magnets, by combining neutron spectroscopy and thermal conductivity measurements. The main issue that we wish to address is excitations and transport in gapless spin chains and ladders with defects (spin impurities). We shall contrast defect physics in double-chain structures (where, classically, a propagating magnetic quasiparticle could bypass a defect), to that in single chains (where chain fragmentation makes defects unavoidable). We also plan to investigate the dependence of defect-induced phenomena on the sign and strength of quasiparticle (spinon) interactions. For these tasks we have selected several target compounds that are known to be almost ideal realizations of basic one dimensional S = 1/2 Heisenberg models. S = 0, S = 1, and S = 3/2 and other types of defects will be introduced by means of chemical substitution. Inelastic neutron scattering experiments will probe the effect of spin defects on the spinon excitation spectrum, with a focus on novel localized and bound defect states. Parallel heat transport measurements will investigate the kinetic aspects of spinon propagation and their interactions with lattice phonons. The ultimate goal will be to connect the findings of these dynamical and kinetic studies in a single physical picture. For most planned avenues of research, tantalizing and very promising preliminary results have already been obtained. The main idea of this DACH joint proposal is to take synergetic advantage of the complementary expertise that has been built up ETH Zurich and IFW Dresden. The group at ETHZ has a long standing record in neutron scattering studies of quantum magnets, but also substantial experience in organic spin systems. The team at IFW Dresden is a recognized leader in magnetic transport studies, and has extensive experience with low-dimensional cupric oxides. The two groups will also pool their arsenal of supplementary characterization methods, including NMR and high-resolution Raman spectroscopy (ETHZ).

• DFG Programme: Research Grants
• International Connection: Switzerland
• Participating Person: Professor Dr. Andrey Zheludev