Weak coupling of pseudoacoustic phonons and magnon dynamics in the incommensurate spin-ladder compound S r14 C u24 O41

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© 2016 American Physical Society.Intriguing lattice dynamics have been predicted for aperiodic crystals that contain incommensurate substructures. Here we report inelastic neutron scattering measurements of phonon and magnon dispersions in Sr14Cu24O41, which contains incommensurate one-dimensional (1D) chain and two-dimensional (2D) ladder substructures. Two distinct pseudoacoustic phonon modes, corresponding to the sliding motion of one sublattice against the other, are observed for atomic motions polarized along the incommensurate axis. In the long wavelength limit, it is found that the sliding mode shows a remarkably small energy gap of 1.7-1.9 meV, indicating very weak interactions between the two incommensurate sublattices. The measurements also reveal a gapped and steep linear magnon dispersion of the ladder sublattice. The high group velocity of this magnon branch and weak coupling with acoustic and pseudoacoustic phonons can explain the large magnon thermal conductivity in Sr14Cu24O41 crystals. In addition, the magnon specific heat is determined from the measured total specific heat and phonon density of states and exhibits a Schottky anomaly due to gapped magnon modes of the spin chains. These findings offer new insights into the phonon and magnon dynamics and thermal transport properties of incommensurate magnetic crystals that contain low-dimensional substructures.






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Chen, X, D Bansal, S Sullivan, DL Abernathy, AA Aczel, J Zhou, O Delaire, L Shi, et al. (2016). Weak coupling of pseudoacoustic phonons and magnon dynamics in the incommensurate spin-ladder compound S r14 C u24 O41. Physical Review B - Condensed Matter and Materials Physics, 94(13). 10.1103/PhysRevB.94.134309 Retrieved from https://hdl.handle.net/10161/12635.

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Olivier Delaire

Associate Professor of the Thomas Lord Department of Mechanical Engineering and Materials Science

The Delaire group investigates atomistic transport processes of energy and charge, and thermodynamics in energy materials. We use a combined experimental and computational approach to understand and control microscopic energy transport for the design of next-generation materials, in particular for sustainable energy applications. Current materials of interest include superionic conductors, photovoltaics, thermoelectrics, ferroelectrics/multiferroics, and metal-insulator transitions. Our group's studies provide fundamental insights into  atomic dynamics and elementary excitations in condensed-matter systems (phonons, electrons, spins), their couplings and their effects on macroscopic properties. We probe the microscopic underpinnings of transport and thermodynamics properties by integrating neutron and x-ray scattering, optical spectroscopy, and thermal characterization, together with quantum-mechanical computer simulations.

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