Protonation-induced discrete superconducting phases in bulk FeSe single crystals
Yan Meng, Xiangzhuo Xing, Xiaolei Yi, Bin Li, Nan Zhou, Meng Li, Yufeng Zhang, Wei Wei, Jiajia Feng, Kensei Terashima, Yoshihiko Takano, Yue Sun, Zhixiang Shi
Abstract
The superconducting transition temperature, ${T}_{\mathrm{c}}$, 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-${T}_{\mathrm{c}}$ superconductivity. In this paper, we have found a series of discrete superconducting phases, with a maximum ${T}_{\mathrm{c}}$ up to 44 K, in ${\mathrm{H}}^{+}$-intercalated FeSe single crystals using an ionic liquid gating method. Accompanied with the increase of ${T}_{\mathrm{c}}$, 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-${T}_{\mathrm{c}}$ superconducting phase was also revealed.