FeSe/SrTiO_(3)高温超导体中的电子条纹相

Stripe phase in high-T_(c) superconductor FeSe/SrTiO_(3)

单层FeSe/SrTiO_(3)中的界面超导增强是近年来高温超导领域的重要发现.该体系中SrTiO_(3)衬底对FeSe的超导增强机制已被广泛研究,其调控作用主要表现为两个方面:电荷掺杂和界面电声耦合.然而,关于FeSe薄膜本身的电子特性研究还不够充分.本文介绍该体系超导增强机制的新进展:FeSe薄膜中的电子条纹相及其与超导的关联.通过扫描隧道显微镜结合分子束外延生长技术,对不同厚度的FeSe薄膜进行了系统研究.我们发现FeSe薄膜中电子倾向于排成条纹状结构,并观测到该条纹相随层厚变化显现出从短程到长程的演化.条纹相是一种电子液晶态,它源于薄层FeSe中被增强的电子关联作用.表面电子掺杂一方面会减弱FeSe薄膜中的电子关联作用,逐渐抑制条纹相;另一方面会诱导超导相变,而剩余的条纹相涨落会对超导电性带来额外增强.我们的结果加深了对低维界面超导体系的认识,也揭示了FeSe薄膜本征的特异性,完善了对FeSe/SrTiO_(3)超导增强机制的理解.

The enhancement of superconductivity in one unit-cell FeSe grown on SrTiO_(3)is an important discovery in high-temperature superconductivity.In this system,the crucial role of the SrTiO_(3)substrate has been extensively studied.Its contribution mainly manifests in two aspects:charge transfer and interfacial electronphonon coupling.However,study of the intrinsic properties of the FeSe thin film itself is still insufficient.In this article,we review the latest research progress of the mechanism of the enhancement of superconductivity in FeSe/SrTiO_(3),covering the newly discovered stripe phase and its relationship with superconductivity.By using scanning tunneling microscope and molecular beam epitaxy growth method,we find that the electrons in FeSe thin film tend to form stripe patterns,and show a thickness-dependent evolution of short-range to long-range stripe phase.The stripe phase,a kind of electronic liquid crystal state(smectic),originates from the enhanced electronic correlation in FeSe thin film.Surface doping can weaken the electronic correlation and gradually suppress the stripe phase,which can induce superconductivity as well.More importantly,the remaining smectic fluctuation provides an additional enhancement to the superconductivity in FeSe film.Our results not only deepen the understanding of the interfacial superconductivity,but also reveal the intrinsic uniqueness of the FeSe films,which further refines the mechanism of superconductivity enhancement in FeSe/SrTiO_(3).