engleski

Charge-density wave formation in Sr14-x Cax Cu24 O41

The electrodynamic response of the spin-ladder compound Sr14-x Cax Cu24 O41 (x=0, 3, 9) has been studied from radio frequencies up to the infrared. At temperatures below 250 K a pronounced absorption peak appears around 12 cm -1 in Sr 14 Cu 24 O 41 for the radiation polarized along the chains/ladders (Ei c). In addition a strongly temperature-dependent dielectric relaxation is observed in the kHz - MHz range. We explain this behavior by a charge-density wave which develops in the ladders and produces a phason mode pinned at 12 cm -1 . With increasing x the mode shifts up in frequency and eventually disappears for x=9 because the dimensionality of the system crosses over from one to two dimensions, giving way to the superconducting ground state under pressure.

charge density wave ; superconductivity ; optical response ; dielectric response

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