A Sharp Peak of the Zero-Temperature Penetration Depth at Optimal Composition in BaFe2(As1-xPx)2

K. Hashimoto; K. Cho; T. Shibauchi; S. Kasahara; Y. Mizukami; R. Katsumata; Y. Tsuruhara; T. Terashima; H. Ikeda; M. A. Tanatar; H. Kitano; N. Salovich; R. W. Giannetta; P. Walmsley; A. Carrington; R. Prozorov; Y. Matsuda

doi:10.1126/science.1219821

paper

A Sharp Peak of the Zero-Temperature Penetration Depth at Optimal Composition in BaFe2(As1-xPx)2

arXiv:1212.5632 · doi:10.1126/science.1219821

Abstract

In a superconductor, the ratio of the carrier density, $n$ , to their effective mass, $m^{*}$ , is a fundamental property directly reflecting the length scale of the superfluid flow, the London penetration depth, $I^»_{L}$ . In two dimensional systems, this ratio $n / m^{*}$ ( $\sim 1/ I^»_{L}^{2}$ ) determines the effective Fermi temperature, $T_{F}$ . We report a sharp peak in the $x$ -dependence of $I^»_{L}$ at zero temperature in clean samples of BaFe $_{2}$ (As $_{1 - x}$ P $_{x}$ ) $_{2}$ at the optimum composition $x = 0.30$ , where the superconducting transition temperature $T_{c}$ reaches a maximum of 30\,K. This structure may arise from quantum fluctuations associated with a quantum critical point (QCP). The ratio of $T_{c} / T_{F}$ at $x = 0.30$ is enhanced, implying a possible crossover towards the Bose-Einstein condensate limit driven by quantum criticality.

Main text (5 pages, 4 figures) + Supplementary Materials (5 pages, 5 figures). Published on June 22, 2012