Evidence for non-conventional pairing in Na$\_x$CoO$\_2$$\cdot$yH$\_2$O

Jean-Pascal Rueff; M. Calandra; M. D'astuto; Ph. Leininger; A. Shukla; A. Bossak; M. Krisch; H. Ishii; Y. Cai; P. Badica; T. Sasaki; K. Yamada; K. Togano

arXiv · cond-mat/0601288

Evidence for non-conventional pairing in Na$\_x$CoO$\_2$$\cdot$yH$\_2$O

Jean-Pascal Rueff·M. Calandra·M. D'astuto·Ph. Leininger·A. Shukla·A. Bossak·M. Krisch·H. Ishii·Y. Cai·P. Badica·T. Sasaki·K. Yamada·K. Togano

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Abstract

We report on first investigation of the lattice dynamics in the novel superconducting material Na$\_{0.35}$CoO$\_2$$\cdot$1.3H$\_2$O and the non-hydrated parent compound Na$\_{0.7}$CoO$\_2$ by inelastic x-ray scattering. The measured phonon dispersion along the $Γ-M$ direction show a marked softening with hole doping of two optical phonon branches close to the Brillouin zone boundary. The phonon spectra, dispersion, and softening are well reproduced by first-principle calculations. The calculations indicates that the soft branches are mainly composed of Co-vibration modes. The estimation of the critical temperature based on electron-phonon coupling mechanism undisputedly points to a non-conventional superconducting state in this material.

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Jean-Pascal Rueff, M. Calandra, M. D'astuto, Ph. Leininger, A. Shukla, A. Bossak, M. Krisch, H. Ishii, Y. Cai, P. Badica, T. Sasaki, K. Yamada, K. Togano. 2006-01-13. Evidence for non-conventional pairing in Na$\_x$CoO$\_2$$\cdot$yH$\_2$O. https://arxiv.org/abs/cond-mat/0601288

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