Thursday, May 30, 2013

1305.6719 (Matteo D'Astuto et al.)

Phonon anomalies and lattice dynamics in superconducting oxychlorides

Matteo D'Astuto, Ikuya Yamada, Paola Giura, Lorenzo Paulatto, Andrea Gauzzi, Moritz Hoesch, Michael Krisch, Masaki Azuma, Mikio Takano
We present a comprehensive study of the phonon dispersion in an underdoped, superconducting Ca$_{2-x}$CuO$_2$Cl$_2$ crystal. We interpret the results using lattice dynamical calculations based on a shell model, and we compare the results, to other hole-doped cuprates, in particular to the ones isomorphic to LSCO. We found that an anomalous dip in the Cu-O bond stretching dispersion develops in oxychlorides with a simultaneous marked broadening of the mode. The broadening maximum appear at $\approx (\pi / (2a) ~ 0 ~ 0)$ that corresponds to the charge-modulations propagation vector. Our analysis also suggests that screening effects in calculations may cause an apparent cosine-shaped bending of the Cu-O bond-stretching dispersion along both the ($q$ 0 0) and the ($q$ $q$ 0) directions, that is not observed on the data close to optimal doping. This observation suggests that the discrepancy between experimental data and \textit{ab-initio} calculations on this mode originates from an overestimation of the doping effects on the mode.
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