High pressure effects on the superconductivity in rare-earth-doped CaFe₂As₂

Abstract

High pressure superconductivity in a rare-earth-doped Ca_0.86Pr_0.14Fe₂As₂ single-crystalline sample has been studied up to 12 GPa and temperatures down to 11 K using the designer diamond anvil cell under a quasi-hydrostatic pressure medium. The electrical resistance measurements were complemented by high pressure and low-temperature X-ray diffraction studies at a synchrotron source. The electrical resistance measurements show an intriguing observation of superconductivity under pressure, with T_c as high as ∼51 K at 1.9 GPa, presenting the highest T_c reported in the intermetallic class of 122 iron-based superconductors. The resistive transition observed suggests a possible existence of two superconducting phases at low pressures of 0.5 GPa: one phase starting at T_c1 ∼ 48 K and the other starts at T_c2 ∼ 16 K. The two superconducting transitions show distinct variations with increasing pressure. High pressure and low-temperature structural studies indicate that the superconducting phase is a collapsed tetragonal ThCr₂Si₂-type (122) crystal structure.

Keywords:

• superconductivity
• iron based compounds
• high pressure
• electrical transport
• X-ray diffraction

PACS::

• 62.50-p
• 74.62Fj
• 64.70K-
• 61.50Ks

Acknowledgements

Daniel Cargill acknowledges support from the National Aeronautics and Space Administration (NASA) – Alabama Space Grant Consortium, Research Experiences for Undergraduates (REU) program under Award No. NNX10AJ80H. Walter Uhoya acknowledges support from the Carnegie/Department of Energy (DOE) Alliance Center (CDAC) under grant no. DE-NA0002006. The work at ORNL was supported by the Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division. Portions of this work were performed in a synchrotron facility at HPCAT (Sector 16), Advanced Photon Source (APS) and Argonne National Laboratory. We are grateful to J.E. Mitchell for growing the single crystal of Ca_0.86Pr_0.14Fe₂As₂.