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我院14级本科生作为第一作者在自然合作期刊发表文章

我院14级本科生鹿大川在电子学院李军老师和物理学院王强华老师的指导下,通过构建金兹堡-朗道自由能,理论解释了新型超导体FeSe中的椭圆形磁通,该成果发表在2018年3月8号的自然合作期刊《npj-量子材料》。

超导自1911年被发现以来对人类社会产生了重要的影响,也推进了基础物理的研究。近些年来发现的铜基、铁基高温超导体又为超导研究注入了新的活力,高温超导机理至今仍未解决。在2011年,《科学》杂志报道了清华大学的宋灿立等人在FeSe中首次观察到椭圆形磁通。由于FeSe简单的晶格结构和新奇的低能电子态——向列态与超导态共存,有望通过研究FeSe的超导性质了解高温超导机理,这也吸引了很多实验和理论上的研究。

该工作构建了多个超导序参量和向列态竞争的金兹堡-朗道自由能。通过求解开放边界条件和周期边界条件下的含时金兹堡-朗道方程描绘了FeSe中的椭圆形磁通涡旋的动态演化以及平衡态下的磁通晶格结构。其中向列态与超导序三线性的相互作用可以使s波与d波超导简并,并提高超导转变温度。该理论结果与最近的实验相吻合。

图a, b, c为s波,d波超导序参量和向列态序参量的含时演化。

npj Quantum Materials volume 3, Article number: 12 (2018)

doi:10.1038/s41535-018-0087-2

https://www.nature.com/articles/s41535-018-0087-2

Elliptical vortex and oblique vortex lattice in the FeSe superconductor based on the nematicity and mixed superconducting orders

摘要 The electronic nematic phase is characterized as an ordered state of matter with rotational symmetry breaking, and has been well studied in the quantum Hall system and the high-T c superconductors, regardless of cuprate or pnictide family. The nematic state in high-T c systems often relates to the structural transition or electronic instability in the normal phase. Nevertheless, the electronic states below the superconducting transition temperature is still an open question. With high-resolution scanning tunneling microscope measurements, direct observation of vortex core in FeSe thin films revealed the nematic superconducting state by Song et al. Here, motivated by the experiment, we construct the extended Ginzburg–Landau free energy to describe the elliptical vortex, where a mixed s-wave and d-wave superconducting order is coupled to the nematic order. The nematic order induces the mixture of two superconducting orders and enhances the anisotropic interaction between the two superconducting orders, resulting in a symmetry breaking from C4 to C2. Consequently, the vortex cores are stretched into an elliptical shape. In the equilibrium state, the elliptical vortices assemble a lozenge-like vortex lattice, being well consistent with experimental results.


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