Weak coupling of pseudoacoustic phonons and magnon dynamics in the incommensurate spin-ladder compound Sr14Cu24O41

作     者：Xi Chen Dipanshu Bansal Sean Sullivan Douglas L. Abernathy Adam A. Aczel Jianshi Zhou Olivier Delaire Li Shi 

作者机构：Materials Science and Engineering Program Texas Materials Institute The University of Texas at Austin Austin Texas 78712 USA Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Department of Mechanical Engineering The University of Texas at Austin Austin Texas 78712 USA Department of Mechanical Engineering and Materials Science Duke University Durham North Carolina 27708 USA 

出 版 物：《Physical Review B》 (凝聚态物质与材料物理学)

年 卷 期：2016年第94卷第13期

页      面：134309-134309页

核心收录：

学科分类：07[理学] 0702[理学-物理学] 

基　　金：Office of Basic Energy Sciences Scientific User Facilities Division U.S. Army Research Office U.S. Department of Energy, USDOE Army Research Office, ARO, (W911NF-14-1-0016) Army Research Office, ARO Office of Science, SC Basic Energy Sciences, BES Division of Materials Sciences and Engineering, DMSE, (DE-SC0016166) Division of Materials Sciences and Engineering, DMSE 

主　　题：Magnons Phonons Inelastic neutron scattering Spin ladders 

摘      要：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.