Condensed-Matter Physics & Materials Science Seminar

"Optical properties of NaxCoO2 single crystals"

Presented by Nan Lin Wang, Institute of Physics, Chinese Academy of Sciences, China

Thursday, September 21, 2006, 1:30 pm — Small Seminar Room, Bldg. 510

Layered NaxCoO2 system has generated great interests in the condensed matter community for it realizes a triangular lattice with partially filled strongly correlated electronic states. With change of Na content x, a rich phase diagram was revealed. We present in-plane optical measurement over broad frequencies on this system with 0.18x0.92. We find that the optical spectral weight increases monotonously with decreasing x from the band insulator x=1. The evolution suggests against a doped Mott insulator for NaxCoO2 system. For all samples, the low-lying charge excitations are rather different from that of a simple Drude metal. A peak at finite frequency in optical conductivity is commonly observed, irrespective of a positive slope of the dc resistivity. The optical data also reveal peculiar spectral feature that is likely caused by a combination of pseudogap and electron-Boson coupling effect. For the charge-ordered sample, an electronic resonance near 800 cm-1 develops below 100 K, and a small charge gap opens upon entering the charge-ordering state.

Hosted by: G. D. Gu

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