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arXiv · 1401.6257

Two distinct superconducting states in KFe$_2$As$_2$ under high pressure

Taichi Terashima·Kunihiro Kihou·Kaori Sugii·Naoki Kikugawa·Takehiko Matsumoto·Shigeyuki Ishida·Chul-Ho Lee·Akira Iyo·Hiroshi Eisaki·Shinya Uji
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Abstract

We report measurements of ac magnetic susceptibility $\chi_{ac}$ and de Haas-van Alphen (dHvA) oscillations in KFe$_2$As$_2$ under high pressure up to 24.7 kbar. The pressure dependence of the superconducting transition temperature $T_c$ changes from negative to positive across $P_c \sim 18$ kbar as previously reported. The ratio of the upper critical field to $T_c$, i.e, $B_{c2} / T_c$, is enhanced above $P_c$, and the shape of $\chi_{ac}$ vs field curves qualitatively changes across $P_c$. DHvA oscillations smoothly evolve across $P_c$ and indicate no drastic change in the Fermi surface up to 24.7 kbar. Three dimensionality increases with pressure, while effective masses show decreasing trends. We suggest a crossover from a nodal to a full-gap $s$ wave as a possible explanation.

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Taichi Terashima, Kunihiro Kihou, Kaori Sugii, Naoki Kikugawa, Takehiko Matsumoto, Shigeyuki Ishida, Chul-Ho Lee, Akira Iyo, Hiroshi Eisaki, Shinya Uji. 2014-01-24. Two distinct superconducting states in KFe$_2$As$_2$ under high pressure. https://doi.org/10.1103/physrevb.89.134520

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