Comparative study of the phonons in nonsuperconducting BaC6 and superconducting CaC6 using inelastic x-ray scattering

A. C. Walters, C. A. Howard, M. H. Upton, M. P. M. Dean, A. Alatas, B. M. Leu, M. Ellerby, D. F. McMorrow, J. P. Hill, M. Calandra, and F. Mauri
Phys. Rev. B 84, 014511 – Published 25 July 2011

Abstract

The low-energy phonons of two different graphite intercalation compounds (GICs) have been measured as a function of temperature using inelastic x-ray scattering (IXS). In the case of the non-superconductor BaC6, the phonons observed are significantly higher (up to 20%) in energy than those predicted by theory, in contrast to the reasonable agreement found in superconducting CaC6. Additional IXS intensity is observed below 15 meV in both BaC6 and CaC6. It has been previously suggested that this additional inelastic intensity may arise from defect or vacancy modes not predicted by theory [d’Astuto et al., Phys. Rev. B 81, 104519 (2010)]. Here it is shown that this additional intensity can arise directly from the polycrystalline nature of the available samples. Our results show that future theoretical work is required to understand the relationship between the crystal structure, the phonons, and the superconductivity in GICs.

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  • Received 3 February 2011

DOI:https://doi.org/10.1103/PhysRevB.84.014511

©2011 American Physical Society

Authors & Affiliations

A. C. Walters1,2,*, C. A. Howard2, M. H. Upton3,4, M. P. M. Dean4, A. Alatas3, B. M. Leu3, M. Ellerby2, D. F. McMorrow2, J. P. Hill4, M. Calandra5, and F. Mauri5

  • 1ESRF, Polygone Scientifique Louis Néel, 6 rue Jules Horowitz, F-38000 Grenoble, France
  • 2London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom
  • 3Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
  • 4Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
  • 5Université Pierre et Marie Curie, 4 Place Jussieu-case postale 115, F-72252 Paris Cedex 05, France

  • *andrew.walters@esrf.fr

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Vol. 84, Iss. 1 — 1 July 2011

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