Berlin 2018 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 110: Superconductivity: Fe-based Superconductors - 1111 and Others
TT 110.2: Talk
Friday, March 16, 2018, 09:45–10:00, H 3010
Determination of nematic, magnetic and superconducting phase transitions in Co doped LaOFeAs single crystals by NMR — •Piotr Lepucki, Rhea Kappenberger, Saicharan Aswartham, Adam Paul Dioguardi, Bernd Büchner, and Hans-Joachim Grafe — IFW Dresden, Helmholtzstraße 20, 01069 Dresden, Germany
Single crystals are a prerequisite to perform angular dependent NMR measurements in solids. However, these were not available in sufficient size for doped LaOFeAs until recently [1]. Here we present such NMR measurements on single crystals of LaOFeAs doped with 3.4% , 4.1% , and 6.2% Co. The underdoped samples show clear signatures of the nematic transition in the 75As NMR linewidth as well as in the spin lattice relaxation rate, T1−1, and its anisotropy. At lower temperatures, a peak in T1−1 signals the onset of long-range magnetic order, whereas the superconducting transition cannot be determined unambiguously in a magnetic field of 7 T, which has been applied for the NMR measurements. In contrast, the optimally doped sample with 6.2% Co shows neither nematic nor long range magnetic order. Instead, T1−1 decreases at the superconducting transition, indicating bulk superconductivity at Tc = 12 K even in an applied field of 7 T. Our NMR results in Co doped LaOFeAs single crystals are broadly consistent with those obtained in Co doped BaFe2As2.
R. Kappenberger et al., J. Cryst. Growth 483, 9 (2018)