Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 23: Posters Superconductivity, Solids at Low Temperature

TT 23.15: Poster

Montag, 7. März 2005, 14:00–18:00, Poster TU D

Reversible and irreversible magnetostrictive effects in untwinned YBa₂Cu₃O₇ crystals — •P. Popovich¹, R. Lortz^1,2,3, C. Meingast¹, S. Tajima⁴, and T. Masui⁴ — ¹Forschungszentrum Karlsruhe, IFP, Germany — ²Fakultät für Physik, Universität Karlsruhe, Germany — ³present address: DCMP, University of Geneva, Switzerland — ⁴ISTEC, Tokyo, Japan

The magnetostriction coefficients, λ_i=1/L_i· dL_i/dH (i=a,b,c), of high-pressure oxygenated untwinned YBa₂Cu₃O₇ single crystals are determined between 40 K and 150 K and in fields up to 10 T. Above 55K, λ is nearly reversible and is, thus, proportional to the uniaxial pressure dependence of the magnetization, which in turn provides important information about the pressure dependencies of T_c(H), the vortex melting transition T_m(H), the thermodynamical critical field H_c(T=0), κ, and the normal state susceptibility. Clear signatures in λ(H) are seen at T_m(H) and at the broadened H_c2. Both transitions exhibit good 3D-XY scaling, which clearly demonstrate the importance of thermal phase fluctuations. The driving force for most of the reversible magnetostriction is due to dT_c/dp_i. Below 55K and above 6-8T, λ(H) becomes irreversible due to increased flux pinning at the order-disorder Bose-glass to vortex-glass transition. In contrast to the magnetization, which shows the typical monotonic peak effect, the irreversible magnetostriction exhibits reproducible fine structure within the transition region. This may be due to nucleation of distinct vortex domains in the crystal, which would provide clear evidence for a first-order transition.