Quantum phase transition of correlated iron-based superconductivity in LiFe${}_{1-x}$Co${}_x$As

Abstract

The interplay between unconventional Cooper pairing and quantum states associated with atomic scale defects is a frontier of research with many open questions. So far, only a few of the high-temperature superconductors allow this intricate physics to be studied in a widely tunable way. We use scanning tunneling microscopy (STM) to image the electronic impact of Co atoms on the ground state of the LiFe${}_{1-x}$Co${}_x$As system. We observe that impurities progressively suppress the global superconducting gap and introduce low energy states near the gap edge, with the superconductivity remaining in the strong-coupling limit. Unexpectedly, the fully opened gap evolves into a nodal state before the Cooper pair coherence is fully destroyed. Our systematic theoretical analysis shows that these new observations can be quantitatively understood by the nonmagnetic Born-limit scattering effect in a s$\pm$-wave superconductor, unveiling the driving force of the superconductor to metal quantum phase transition.

22 pages, 12 figures, includes Supplementary Materials. To appear in Phys. Rev. Lett

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Cited by in corpus (1)

• On the Remarkable Superconductivity of FeSe and its Close Cousins