P-T phase diagram of iron arsenide superconductor NdFeAsO_0.88F_0.12

¹ Geophysical Laboratory, Carnegie Institution of Washington - 5251 Broad Branch Road NW, Washington DC 20015, USA
² Institute of Crystallography, Russian Academy of Sciences - Leninsky pr. 59, Moscow 119333, Russia
³ Institute for Nuclear Research, Russian Academy of Sciences - Troitsk, Moscow 142190, Russia
⁴ L.V. Kirensky Institute of Physics, Siberian Branch of Russian Academy of Sciences - Krasnoyarsk 660036, Russia
⁵ Siberian Federal University - 79 Svobodny Prospect, Krasnoyarsk 660041, Russia
⁶ Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin Austin TX 78712-0254, USA
⁷ Beijing National Lab for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences P. O. Box 603, Beijing 100190, China

^(a) gavriliuk@mail.ru

Received: 20 August 2012
Accepted: 6 November 2012

Abstract

NdFeAsO_0.88F_0.12 belongs to the recently discovered family of high-T_C iron-based superconductors. We have studied the influence of high pressure on transport properties of this material at low temperatures using the four-probe electrical conductivity technique in a diamond cell. Contrary to La-based compounds, we did not observe a maximum in T_C under pressure. Under compression, T_C drops rapidly as a linear function of pressure with the slope k = −2.8 ± 0.1 K/GPa. Under decompression, the behavior is completely reversible. The extrapolated value of T_C at zero pressure is about T_C (0) = 51.7 ± 0.4 K. At pressures higher than ∼18.4 GPa, the superconducting state disappears at all measured temperatures, although electrical resistance changes slope dramatically and shows a concave behavior. These observations may be related to the Kondo effect or to a weak localization of two-dimensional carriers at high pressures and low temperatures below ∼45 K, indicating a competition mechanism with the superconducting phase. On the bases of our experimental data, we propose a tentative P-T phase diagram of NdFeAsO_0.88F_0.12.