Regensburg 2002 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 22: Postersitzung III: Syst. korr. Elektr.: Theorie II (1-15), Metall-Isol.- und Phasenüberg
änge (16-33), SL: Massivmat., Bandl., Pinning, Vortexdyn., Transport, Korngr. (34-43), Niedrigdim. Syst., Magnetotransport (44-63)

TT 22.44: Poster

Donnerstag, 14. März 2002, 14:00–17:30, A

Charge Density Waves in (Ca,Sr)₁₄Cu₂₄O₄₁ — •B. Gorshunov¹, T. Rõõm¹, P. Haas¹, M. Dressel¹, V. Vuletic², B. Hamzic², S. Tomic², and J. Akimitsu³ — ¹1. Physikalisches Institut, Universität Stuttgart — ²Institute of Physics, Zagreb, Croatia — ³ADSM, Hiroshima University, Higashi-Hiroshima, Japan

Spectra of conductivity, dielectric constant and loss function of Sr_14−xCa_xCu₂₄O₄₁ crystals are measured along a, b, and c axes in a broad frequency interval from radiofrequencies to the infrared, 10⁻¹⁰ to 10⁴ cm⁻¹, at temperatures 5 − 300 K. A low-energy mode centered at 12 cm⁻¹ is discovered in the c-axis response in the Ca-free compound Sr₁₄Cu₂₄O₄₁ which shifts to higher frequency with Ca-doping at x=3 and disappears for x=9. At radio frequencies a strong relaxation is observed in the spectra of the complex dielectric function of Sr₁₄Cu₂₄O₄₁. The temperature evolution of the observed features allows to relate them to a CDW formed in the ladders. In the presence of uncondensed free carriers and for non-uniform pinning, the CDW produces a pinned phason mode at 12 cm⁻¹ and corresponding dissipation at radio frequencies due to single-particles currents which screen the moving CDW.