# Thermodynamic phase diagram of FeSe${0.5}$Te${0.5}$ single crystals up to 28 Tesla - Condensed Matter > Superconductivity

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Abstract: We report on specific heat $C p$, transport, Hall probe and penetrationdepth measurements performed on FeSe${0.5}$Te${0.5}$ single crystals $T c\sim 14$ K. The thermodynamic upper critical field $H {c2}$ lines has beendeduced from $C p$ measurements up to 28 T for both $H\|c$ and $H\|ab$, andcompared to the lines deduced from transport measurements up to 55 T in pulsedmagnetic fields. We show that this {\it thermodynamic} $H {c2}$ line presentsa very strong downward curvature for $T ightarrow T c$ which is not visiblein transport measurements. This temperature dependence associated to an upwardcurvature of the field dependence of the Sommerfeld coefficient confirm that$H {c2}$ is limited by paramagnetic effects. Surprisingly this paramagneticlimit is visible here up to $T-T c \sim 0.99$ for $H\|ab$ which is theconsequence of a very small value of the coherence length $\xi c0 \sim 4 \AA$and $\xi {ab}0 \sim 15 \AA$, confirming the strong renormalisation of theeffective mass as compared to DMFT calculations previously observed in ARPESmeasurements Phys. Rev. Lett. 104, 097002 2010. $H {c1}$ measurements leadto $\lambda {ab}0 = 430 \pm 50$ nm and $\lambda c0 = 1600 \pm 200$ nm andthe corresponding anisotropy is approximatively temperature independent $\sim4$, being close to the anisotropy of $H {c2}$ for $T ightarrow T c$. Thetemperature dependence of both $\lambda$ $\propto T^2$ and the electroniccontribution to the specific heat confirm the non conventional couplingmechanism in this system.

Autor: T. Klein, D. Braithwaite, A. Demuer, W. Knafo, G. Lapertot, C. Marcenat, P. Rodieere, I. Sheikin, P. Strobel, A. Sulpice, P. Toul

Fuente: https://arxiv.org/