Critical current enhancement driven by suppression of superconducting fluctuation in ion-gated ultrathin FeSe
Critical current enhancement driven by suppression of superconducting fluctuation in ion-gated ultrathin FeSe
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DOI：
10.1088/1361-6668/aab4ea
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发表时间：
2018-05
影响因子：
3.6
通讯作者：
T. Harada;J. Shiogai;T. Miyakawa;Tsutomu Nojima;Atsushi Tsukazaki
中科院分区：
文献类型：
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作者：
T. Harada;J. Shiogai;T. Miyakawa;Tsutomu Nojima;Atsushi Tsukazaki
相变的框架，如超导相变，有时取决于材料的尺寸。在二维薄膜的实验条件下，由于对缺陷和界面效应的脆弱超导状态，超导性往往被削弱。与这一趋势相反，FeSe薄极限的超导性表现出相反的趋势，如临界温度（Tc）的增加和超导间隙超过体值；然而，主导机制仍在争论中。在这里，我们测量了离子门控FeSe薄膜的厚度相关的电输运特性，以评估超薄FeSe中的超导临界电流（Ic）。通过电化学刻蚀技术系统地降低霍尔条形双电层晶体管的FeSe厚度，我们观察到在最薄的条件下，Ic的显著增强达到约10 mA，对应于约107 a cm−2。通过对跃迁行为的分析，我们明确了抑制超导涨落是离子门控超薄FeSe薄膜中大Ic的来源之一。这些结果表明，在FeSe的薄极限上，存在一个可能具有致密库珀对的鲁棒超导态。
The framework of phase transition, such as superconducting transition, occasionally depends on the dimensionality of materials. Superconductivity is often weakened in the experimental conditions of two-dimensional thin films due to the fragile superconducting state against defects and interfacial effects. In contrast to this general trend, superconductivity in the thin limit of FeSe exhibits an opposite trend, such as an increase in critical temperature (Tc) and the superconducting gap exceeding the bulk values; however, the dominant mechanism is still under debate. Here, we measured thickness-dependent electrical transport properties of the ion-gated FeSe thin films to evaluate the superconducting critical current (Ic) in the ultrathin FeSe. Upon systematically decreasing the FeSe thickness by the electrochemical etching technique in the Hall bar-shaped electric double-layer transistors, we observed a dramatic enhancement of Ic reaching about 10 mA and corresponding to about 107 A cm−2 in the thinnest condition. By analyzing the transition behavior, we clarify that the suppressed superconducting fluctuation is one of the origins of the large Ic in the ion-gated ultrathin FeSe films. These results indicate the existence of a robust superconducting state possibly with dense Cooper pairs at the thin limit of FeSe.