Regensburg 2002 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 7: Postersitzung I: Anwendungen der Supraleitung (1-6), Dünne Schichten, Josephsonkontakte, SQUIDs (7-17), Neue und unkonv. Supraleiter(18-23), Amorphe- und Tunnelsyst. (24-28), Quantenflüssigkeiten (29-30), Syst. korr. Elektr.: Theorie I (31-45)

TT 7.20: Poster

Montag, 11. März 2002, 14:30–18:00, A

Evidence of reentrant superconductivity in a diluted Van Vleck paramagnet — •Thomas Herrmannsdoerfer and Frank Pobell — Forschungszentrum Rossendorf, Postfach 51 01 19, D-01314 Dresden

Compared to magnetically doped superconductors described by the theory of Abrikosov and Gorkov [1], electronic singlet ground state systems can have a much larger critical concentration of magnetic impurities [2]. Recent measurements on the quasi binary Van Vleck paramagnet La_1−xPr_xTe revealed a critical Pr³⁺ concentration x close above 0.50. Surprisingly, in La_0.50Pr_0.50Te the superconducting state with T_c = 0.20 K is not stable down to zero temperature but undergoes a reentrant transition at about 0.02 K. This reentrant transition is likely caused by the hyperfine enhanced magnetic moments of the ¹⁴¹Pr nuclei. Although the hyperfine enhanced nuclear moments are not in a magnetically ordered ground state at T = 0.02 K, their impact on superconductivity seems to be even stronger than the influence of a nuclear ferromagnetic phase transition on type-I superconductivity observed in AuIn₂ [3]. [1]A. Abrikosov and L. Gorkov, Sov. Phys. JETP 12, 1243 (1961) [2]J. Keller and P. Fulde, J. Low Temp. Phys. 4, 289 (1971) [3]S. Rehmann, T. Herrmannsdoerfer and F. Pobell, Phys. Rev. Lett. 78, 1122 (1997)