Emergence of Superconductivity from Fully Incoherent Normal State in an Iron-Based Superconductor (Ba$_{0.6}$K$_{0.4}$)Fe$_2$As$_2$

Jianwei Huang; Lin Zhao; Cong Li; Qiang Gao; Jing Liu; Yong Hu; Yu Xu; Yongqing Cai; Dingsong Wu; Ying Ding; Cheng Hu; Huaxue Zhou; Xiaoli Dong; Guodong Liu; Qingyan Wang; Shenjin Zhang; Zhimin Wang; Fengfeng Zhang; Feng Yang; Qinjun Peng; Zuyan Xu; Chuangtian Chen; Xingjiang Zhou

doi:10.1016/j.scib.2018.11.017

paper

Emergence of Superconductivity from Fully Incoherent Normal State in an Iron-Based Superconductor (Ba $_{0.6}$ K $_{0.4}$ )Fe $_{2}$ As $_{2}$

arXiv:1901.05693 · doi:10.1016/j.scib.2018.11.017

Abstract

In unconventional superconductors, it is generally believed that understanding the physical properties of the normal state is a pre-requisite for understanding the superconductivity mechanism. In conventional superconductors like niobium or lead, the normal state is a Fermi liquid with a well-defined Fermi surface and well-defined quasipartcles along the Fermi surface. Superconductivity is realized in this case by the Fermi surface instability in the superconducting state and the formation and condensation of the electron pairs (Cooper pairing). The high temperature cuprate superconductors, on the other hand, represent another extreme case that superconductivity can be realized in the underdoped region where there is neither well-defined Fermi surface due to the pseudogap formation nor quasiparticles near the antinodal regions in the normal state. Here we report a novel scenario that superconductivity is realized in a system with well-defined Fermi surface but without quasiparticles along the Fermi surface in the normal state. High resolution laser-based angle-resolved photoemission measurements have been performed on an optimally-doped iron-based superconductor (Ba $_{0.6}$ K $_{0.4}$ )Fe $_{2}$ As $_{2}$ . We find that, while sharp superconducting coherence peaks emerge in the superconducting state on the hole-like Fermi surface sheets, no quasiparticle peak is present in the normal state. Its electronic behaviours deviate strongly from a Fermi liquid system. The superconducting gap of such a system exhibits an unusual temperature dependence that it is nearly a constant in the superconducting state and abruptly closes at T $_{c}$ . These observations have provided a new platform to study unconventional superconductivity in a non-Fermi liquid system.

22 pages, 4 figures

Emergence of Superconductivity from Fully Incoherent Normal State in an Iron-Based Superconductor (Ba $_{0.6}$ K $_{0.4}$ )Fe $_{2}$ As $_{2}$

Abstract

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Emergence of Superconductivity from Fully Incoherent Normal State in an Iron-Based Superconductor (Ba0.6​K0.4​)Fe2​As2​

Abstract

References in corpus (15)

Cited by in corpus (3)

Emergence of Superconductivity from Fully Incoherent Normal State in an Iron-Based Superconductor (Ba $_{0.6}$ K $_{0.4}$ )Fe $_{2}$ As $_{2}$