Protonation-induced discrete superconducting phases in bulk FeSe single crystals
Abstract
The superconducting transition temperature, Tc, of FeSe can be significantly enhanced several-fold by applying pressure, electron doping, intercalating spacing layer, and reducing dimensionality. Various ordered electronic phases, such as nematicity and spin density waves, have also been observed accompanying high-Tc superconductivity. Investigation on the evolution of the electronic structure with Tc is essential to understanding electronic behavior and high-Tc superconductivity in FeSe and its derived superconductors. In this report, we have found a series of discrete superconducting phases, with a maximum Tc up to 44 K, in H+-intercalated FeSe single crystals using an ionic liquid gating method. Accompanied with the increase of Tc, suppression of the nematic phase and evolution from non-Fermi-liquid to Fermi-liquid behavior was observed. An abrupt change in the Fermi surface topology was proposed to explain the discrete superconducting phases. A band structure that favors the high-Tc superconducting phase was also revealed.
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