Thermodynamic phase diagram of Fe(Se0.5Te0.5) single crystals in fields up to 28 tesla

Thierry Klein (1) , D. Braithwaite (2) , A. Demuer (3) , William Knafo (4) , G. Lapertot (2) , C. Marcenat (2) , Pierre Rodière (1) , I. Sheikin (3) , Pierre Strobel (5) , André Sulpice (1) , Pierre Toulemonde (5)

1 NEEL - MagSup - Magnétisme et Supraconductivité
2 SPSMS - UMR 9001 - Service de Physique Statistique, Magnétisme et Supraconductivité
3 LNCMI-G - Laboratoire national des champs magnétiques intenses - Grenoble
4 LNCMI-T - Laboratoire national des champs magnétiques intenses - Toulouse
5 NEEL - MRS - Matériaux, Rayonnements, Structure

We report on specific heat Cp , transport, Hall probe, and penetration depth measurements performed on Fe Se0.5Te0.5 single crystals Tc 14 K . The thermodynamic upper critical field Hc2 lines has been deduced from Cp measurements up to 28 T for both H c and H ab, and compared to the lines deduced from transport measurements up to 55 T in pulsed magnetic fields . We show that this thermodynamic Hc2 line presents a very strong downward curvature for T→Tc which is not visible in transport measurements. This temperature dependence associated to an upward curvature of the field dependence of the Sommerfeld coefficient confirms that Hc2 is limited by paramagnetic effects. Surprisingly this paramagnetic limit is visible here up to T/Tc 0.99 for H ab which is the consequence of a very small value of the coherence length c 0 4 Å and ab 0 15 Å , confirming the strong renormalization of the effective mass as compared to DMFT calculations previously observed in ARPES measurements A. Tamai, A. Y. Ganin, E. Rozbicki, J. Bacsa, W. Meevasana, P. D. C. King, M. Caffio, R. Schaub, S. Margadonna, K. Prassides, M. J. Rosseinsky, and F. Baumberger, Phys. Rev. Lett. 104, 097002 2010 . Hc1 measurements lead to ab 0 =430 50 nm and c 0 =1600 200 nm and the corresponding anisotropy is approximatively temperature independent 4 , being close to the anisotropy of Hc2 for T→Tc. The temperature dependence of both T2 and the electronic contribution to the specific heat confirm the nonconventional coupling mechanism in this system.

Mots clés: supraconductivité

Domaines: Supraconductivité [cond-mat.supr-con]

Thierry Klein, D. Braithwaite, A. Demuer, William Knafo, G. Lapertot, et al.. Thermodynamic phase diagram of Fe(Se0.5Te0.5) single crystals in fields up to 28 tesla. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2010, 82, pp.184506. ⟨10.1103/PhysRevB.82.184506⟩. ⟨hal-00957183⟩