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Low-Energy Charge-Density Excitations in MgB$_{2}$: Striking Interplay between Single-Particle and Collective Behavior for Large Momenta

Y. Q. Cai·P. C. Chow·O. D. Restrepo·Y. Takano·K. Togano·H. Kito·H. Ishii·C. C. Chen·K. S. Liang·C. T. Chen·S. Tsuda·S. Shin·C. C. Kao·W. Ku·A. G. Eguiluz
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Abstract

A sharp feature in the charge-density excitation spectra of single-crystal MgB$_{2}$, displaying a remarkable cosine-like, periodic energy dispersion with momentum transfer ($q$) along the $c^{*}$-axis, has been observed for the first time by high-resolution non-resonant inelastic x-ray scattering (NIXS). Time-dependent density-functional theory calculations show that the physics underlying the NIXS data is strong coupling between single-particle and collective degrees of freedom, mediated by large crystal local-field effects. As a result, the small-$q$ collective mode residing in the single-particle excitation gap of the B $π$ bands reappears periodically in higher Brillouin zones. The NIXS data thus embody a novel signature of the layered electronic structure of MgB$_{2}$.

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Y. Q. Cai, P. C. Chow, O. D. Restrepo, Y. Takano, K. Togano, H. Kito, H. Ishii, C. C. Chen, K. S. Liang, C. T. Chen, S. Tsuda, S. Shin, C. C. Kao, W. Ku, A. G. Eguiluz. 2006-07-13. Low-Energy Charge-Density Excitations in MgB$_{2}$: Striking Interplay between Single-Particle and Collective Behavior for Large Momenta. https://doi.org/10.1103/physrevlett.97.176402

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