1306.5844 (P. Lemmens et al.)

Enhanced low energy fluctuations and increasing out-of-plane coherence
in vacancy ordered NaxCoO2    [PDF]

P. Lemmens, V. Gnezdilov, G. J. Shu, L. Alff, C. T. Lin, B. Keimer, F. C. Chou

We report Raman scattering experiments on the strongly correlated electron system NaxCoO2 with x= 0.71 and ordered Na vacancies. In this doping regime, NaxCoO2 exhibits a large and unusual thermopower and becomes superconducting upon hydration. Our Raman scattering data reveal pronounced low energy fluctuations that diverge in intensity at low temperatures. Related to these fluctuations is a drastic decrease of an electronic scattering rate from 50 to 3 cm-1. This observation is quite different from the behavior of Na disordered samples that have a larger and temperature independent scattering rate. Simultaneously with the evolution of the scattering rate, phonon anomalies point to an increasing out-of-plane coherence of the lattice with decreasing temperature. These observations may indicate the condensation of spin polarons into an unusual, highly dynamic ground state.

View original: http://arxiv.org/abs/1306.5844