Enhancement of Superconductivity Linked with Linear-in-Temperature/Field Resistivity in Ion-Gated FeSe Films

11 Mar 2021  ·  Xingyu Jiang, Mingyang Qin, Xinjian Wei, Zhongpei Feng, Jiezun Ke, Haipeng Zhu, Fucong Chen, Liping Zhang, Li Xu, Xu Zhang, Ruozhou Zhang, Zhongxu Wei, Peiyu Xiong, Qimei Liang, Chuanying Xi, Zhaosheng Wang, Jie Yuan, Beiyi Zhu, Kun Jiang, Ming Yang, Junfeng Wang, Jiangping Hu, Tao Xiang, Brigitte Leridon, Rong Yu, Qihong Chen, Kui Jin, Zhongxian Zhao ·

Iron selenide (FeSe) - the structurally simplest iron-based superconductor, has attracted tremendous interest in the past years. While the transition temperature (Tc) of bulk FeSe is $\sim$ 8 K, it can be significantly enhanced to 40 - 50 K by various ways of electron doping. However, the underlying physics for such great enhancement of Tc and so the Cooper pairing mechanism still remain puzzles. Here, we report a systematic study of the superconducting- and normal-state properties of FeSe films via ionic liquid gating. With fine tuning, Tc evolves continuously from below 10 K to above 40 K; in situ two-coil mutual inductance measurements unambiguously confirm the gating is a uniform bulk effect. Close to Tc, the normal-state resistivity shows a linear dependence on temperature and the linearity extends to lower temperatures with the superconductivity suppressed by high magnetic fields. At high fields, the normal-state magnetoresistance exhibits a linear-in-field dependence and obeys a simple scaling relation between applied field and temperature. Consistent behaviors are observed for different-Tc states throughout the gating process, suggesting the pairing mechanism very likely remains the same from low- to high-Tc state. Importantly, the coefficient of the linear-in-temperature resistivity is positively correlated with Tc, similarly to the observations in cuprates, Bechgaard salts and iron pnictide superconductors. Our study points to a short-range antiferromagnetic exchange interaction mediated pairing mechanism in FeSe.

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Superconductivity