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Phonon softening and anomalous mode near the xc = 0.5 quantum critical point inCa2-xSrxRuO4



R. G. Moore, M. D. Lumsden, M. B. Stone, Jiandi Zhang, Ying Chen, Jeffrey Lynn, R. Jin, D Mandrus, E. W. Plummer


Inelastic neutron scattering is used to measure the temperature-dependent phonon dispersion in Ca2−xSrxRuO4(x=0.4,0.6). The in-plane Σ4 octahedral tilt mode softens significantly at the zone boundary of the high-temperature tetragonal (HTT) I41/acd structure as the temperature approaches the transition to a low-temperature orthorhombic (LTO) Pbca phase. This behavior is similar to that in La2CuO4, but an inelastic feature that is not found in the cuprate is present. An anomalous phonon mode is observed at energy transfers greater than the Σ4, albeit with similar dispersion. This anomalous phonon mode never softens below ∼5 meV, even for temperatures below the HTT-LTO transition. This mode is attributed to the presence of intrinsic structural disorder within the I41/acd tetragonal structure of the doped ruthenate.
Physical Review B


inelastic neutron scattering, soft phonons, structural phase transition, quantum critical point, anomalous phonon mode


Moore, R. , Lumsden, M. , Stone, M. , Zhang, J. , Chen, Y. , Lynn, J. , Jin, R. , Mandrus, D. and Plummer, E. (2009), Phonon softening and anomalous mode near the x<sub>c</sub> = 0.5 quantum critical point inCa<sub>2-x</sub>Sr<sub>x</sub>RuO<sub>4</sub>, Physical Review B, [online],, (Accessed April 19, 2024)
Created May 4, 2009, Updated March 25, 2024