Regensburg 2000 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 17: Postersitzung II: Pinning und Vortexdynamik (1-8), Supraleitung: Theorie (9-13), Korrelierte Elektronen (14-48), Niederdimensionale Systeme (49-68), Quantenflüssigkeiten (69-75)

TT 17.62: Poster

Mittwoch, 29. März 2000, 14:30–18:00, A

Thermodynamic properties of the chains in (Sr,Ca,La)₁₄Cu₂₄O₄₁ — •U. Ammerahl^1,2, C. Kerpen¹, B. Büchner¹, R. Gross¹, and A. Revcolevschi² — ¹Lehrstuhl für Angewandte Physik, II. Physikalisches Institut, Universität zu Kvln, Z|lpicher Str. 77, D-50937 Kvln — ²Universitii Paris-Sud, 91405 Orsay Cidex, France

Measurements of the thermal expansion along the principal axes of Sr_14−xCa_xCu₂₄O₄₁ (0≤ x ≤ 12) single crystals were performed. Anomalous magnetic contributions along the chains were observed which are ascribed to the formation of the spin-gap state. From thermodynamic relations it was found that uniaxial pressure along the chains increases the spin-gap by 2 K/GPa. Additional anomalous contributions along the a and c axes, which depend sensitively on the Ca concentration, give strong evidence for short-range low-dimensional charge order within the chains. Specific heat measurements of a Ca₉La₅Cu₂₄O₄₁ single crystal in magnetic fields up to 14 T along the three principal axes were carried out. Anomalies of the specific heat indicating long-range antiferromagnetic order are strongly field-dependent and exhibit an extreme anisotropy with respect to the magnetic field orientation. In addition, large magnetic contributions to the specific heat above the phase transition were observed revealing the low dimensional character of the chains. Supported by the DFG.