Berlin 2012 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 33: Superconductivity, Measuring Devices, Matter at Low Temperature: Poster Session

TT 33.4: Poster

Wednesday, March 28, 2012, 15:00–19:00, Poster B

Evidence for vortex lattice melting in Ba_1−xK_xFe₂As₂ seen by thermal expansion — •Philipp Burger^1,2, Anna Böhmer^1,2, Frédéric Hardy¹, Peter Adelmann¹, Doris Ernst¹, Rainer Fromknecht¹, Peter Schweiss¹, Thomas Wolf¹, Hilbert von Löhneysen^1,3, and Christoph Meingast¹ — ¹Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany — ²Fakultät für Physik, Karlsruher Institut für Technologie, 76128 Karlsruhe, Germany — ³Physikalisches Institut, Karlsruher Institut für Technologie, 76128 Karlsruhe, Germany

Low temperature thermal expansion measurements have been performed on underdoped (T_c=30.6 K) and overdoped (T_c=33.8 K) Ba_1−xK_xFe₂As₂ single crystals in magnetic fields up to 10T applied perpendicular to the Fe-As layers. The superconducting transition for the underdoped sample broadens strongly with increasing magnetic field due to strong fluctuations, whereas for the overdoped sample it simply shifts to lower temperatures. Upon heating (after cooling in constant field) we observe a sharp peak in the expansion coefficients at a temperature slightly lower than T_c. These peaks are absent in the cooling curves. We associate these peaks with an underlying thermodynamic melting of the vortex lattice, since our results are very similiar to previous thermal expansion data [1] of YBCO, which clearly exhibits a first-order vortex melting transition.
R. Lortz et al., J. Low Temp. Phys 147, 365 (2007)