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論文

Collapse of Jahn-Teller phonons in La$$_{1-x}$$Sr$$_{x}$$MnO$$_{3}$$ with weak magnetoresistance

Sterling, T. C.*; Savici, A. T.*; 梶本 亮一; 池内 和彦*; Khan, N.*; Weber, F.*; Reznik, D.*

Communications Materials (Internet), 32 Pages, 2026/00

https://doi.org/10.1038/s43246-026-01139-4

We investigated phonons and spin-phonon coupling in ferromagnetic colossal magnetoresistance (CMR) manganites La$$_{1-x}$$Sr$$_{x}$$MnO$$_{3}$$ ($$x =0.2,0.3$$) that have a relatively small CMR associated with the melting of the magnetic order above room temperature. High-resolution neutron scattering experiments combined with density functional theory (DFT) show that the low-temperature ferromagnetic phase is conventional: neutron scattering intensities from phonons agree with DFT predictions, magnons follow sinusoidal dispersions, and no phonon-magnon hybridization occurs. Fluctuations of Mn moments and low-energy phonons involving Mn and La vibrations remain conventional in the high temperature paramagnetic phase, indicating that the Mn and La/Sr sublattices are not strongly perturbed by the melting of magnetic order. In sharp contrast, the Jahn-Teller active optical oxygen vibrations collapse entirely above the Curie temperature, in spite of the low CMR in these compositions, with at least part of the lost spectral weight reappearing as quasielastic scattering. We attribute this highly anomalous behavior to giant electron-phonon coupling (EPC) in the charge and/or orbital channel. It drives cooperative diffusive motion of quasistatic carrier-trapping oxygen sublattice distortions once ferromagnetism disappears. We hypothesize that the magnitude of magnetoresistance correlates with the rate of this diffusion rather than with the strength of Jahn-Teller EPC.

論文

Muon spin rotation measurements of heterogeneous field response in overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$

MacDougall, G. J.*; Savici, A. T.*; Aczel, A. A.*; Birgeneau, R. J.*; Kim, H.*; Kim, S.-J.*; 伊藤 利充*; Rodriguez, J. A.*; Russo, P. L.*; 植村 泰朋*; et al.

Physical Review B, 81(1), p.014508_1 - 014508_7, 2010/01

https://doi.org/10.1103/PhysRevB.81.014508
 被引用回数：11 パーセンタイル：43.88(Materials Science, Multidisciplinary)

Transverse-field muon spin rotation measurements of overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ reveal a large broadening of the local magnetic field distribution in response to applied field, persisting to high temperatures. The field response is approximately Curie-Weiss-like in temperature and is largest for the highest doping investigated. Such behavior is contrary to the canonical Fermi-liquid picture commonly associated with the overdoped cuprates and implies extensive heterogeneity in this region of the phase diagram. A possible explanation for the result lies in regions of staggered magnetization about dopant cations, analogous to what is argued to exist in underdoped systems.

論文

Muon spin rotation study of field-induced magnetism in heavily overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$

MacDougall, G. J.*; Birgeneau, R. J.*; Kim, H.*; Kim, S.-J.*; Rodriguez, J.*; Russo, P. L.*; Savici, A. T.*; 植村 泰朋*; 脇本 秀一; Wiebe, C. R.*; et al.

Physica B; Condensed Matter, 374-375, p.211 - 214, 2006/03

https://doi.org/10.1016/j.physb.2005.11.056
 被引用回数：4 パーセンタイル：21.53(Physics, Condensed Matter)

高温超伝導体の研究において、単結晶試料育成や化学的ドーピングの困難から、過剰ドープ領域の研究はほとんどなされていなかった。本研究では、世界初となる過剰ドープしたLa$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$単結晶の$$mu$$SR実験の結果を報告する。縦磁場$$mu$$SRの結果から、relaxation rateの温度依存性がCurie-Weiss則に従い、そのCurie constantが磁場の関数として$$Cproptoalpha H$$と書かれることが見いだされた。この現象は、内部磁場分布の異常が磁場により誘起されていることを示している。磁場誘起の度合を表す$$alpha$$は$$x=0.12$$から既に現れ、過剰ドープ領域の$$x=0.30$$まで単調増加し、ドープ量に依存することがわかった。この磁場誘起による異常な内部磁場分布の原因の解明は、今後の重要な課題である。

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