Evolution of quasiparticle excitations with critical mass enhancement in superconducting AFe2As2 (A = K, Rb, and Cs)

Y. Mizukami; Y. Kawamoto; Y. Shimoyama; S. Kurata; H. Ikeda; T. Wolf; D. A. Zocco; K. Grube; H. v. Löhneysen; Y. Matsuda; T. Shibauchi

doi:10.1103/PhysRevB.94.024508

paper

Evolution of quasiparticle excitations with critical mass enhancement in superconducting AFe2As2 (A = K, Rb, and Cs)

arXiv:1510.02273 · doi:10.1103/PhysRevB.94.024508

Abstract

In the heavily hole-doped iron-based superconductors $A$ Fe $_{2}$ As $_{2}$ ( $A =$ K, Rb, and Cs), the electron effective mass increases rapidly with alkali-ion radius. To study how the mass enhancement affects the superconducting state, we measure the London penetration depth $λ (T)$ in clean crystals of $A$ Fe $_{2}$ As $_{2}$ down to low temperature $T \sim 0.1$ K. In all systems, the superfluid stiffness $ρ_{s} (T) = λ^{2} (0) / λ^{2} (T)$ can be approximated by a power-law $T$ dependence at low temperatures, indicating the robustness of strong momentum anisotropy in the superconducting gap $Δ (k)$ . The power $α$ increases from $\sim 1$ with mass enhancement and approaches an unconventional exponent $α \sim 1.5$ in the heaviest CsFe $_{2}$ As $_{2}$ . This appears to be a hallmark of superconductors near antiferromagnetic quantum critical points, where the quasiparticles excited across the anisotropic $Δ (k)$ are significantly influenced by the momentum dependence of quantum critical fluctuations.

main text: 6 pages, 4 figures, 1 table; supplemental material:2 pages, 1 figure

Evolution of quasiparticle excitations with critical mass enhancement in superconducting AFe2As2 (A = K, Rb, and Cs)

Abstract

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