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1、FeSe 单晶的高压研究进展 孙建平 王铂森 程金光 中国科学院物理研究所 中国科学院大学物理学院 摘 要： FeSe 及其衍生化合物是近年来铁基高温超导领域的研究热点.在常压下, FeSe会首先在 Ts=90 K 形成非磁性的电子向列序, 然后在 Tc8 K 出现超导电性;对FeSe 施加压力会诱导长程反铁磁序, 在更高压力下实现 Tc37 K 的高温超导.澄清高温超导与正常态电子向列序和长程反铁磁序的关系对阐明高温超导机理具有重要意义.针对这一问题, 利用立方六面砧高压装置对 FeSe 单晶开展了较详细的高压电输运性质测量, 取得了重要进展.首先, 绘制了 FeSe 单晶完整的温度-压力相
2、图, 具体展示了电子向列序、压致长程反铁磁序和超导相随压力的演化关系, 观察到圆拱形的反铁磁相界 Tm (P) , 并揭示 3 种电子序之间的竞争关系;对应电子向列序和反铁磁序被压制的临界压力, FeSe 的超导转变温度 Tc呈台阶式升高, 最终在 Pc6 GPa 实现了 Tcmax=38.5 K 的高温超导.高压霍尔效应测试表明, 在 2 GPa 附近向列序的消失和反铁磁序的出现伴随着费米面重构, 正常态从电子型载流子主导转变为空穴型主导, 而且霍尔系数在 Pc (即 Tcmax附近出现显著增强, 表明临界反铁磁涨落对实现高温超导具有重要作用.结合第一性原理计算, 进一步证实 FeSe 在高
3、压下存在电子型与空穴型费米面, 支持与FeA s 基高温超导体系类似的费米面嵌套机制, 对统一理解 FeSe 基和 FeAs 基高温超导机理提供了重要依据.关键词： FeSe; 高压调控; 非常规超导; 磁性量子临界点; 作者简介：程金光 E-mail: 收稿日期：2017-06-28基金：国家自然科学基金 (11574377) Recent progress on the high-pressure studies of FeSe single crystalSUN JianPing WANG BoSen CHENG JinGuang Institute of Physics, Chines
4、e Academy of Sciences; Abstract： Among the iron-based superconductors, the structurally simplest FeSe and FeSe-derived materials have attracted enormous research interest recently due to its unusual electronic properties and the great tunability of the superconducting transition temperature Tc. For
5、the bulk FeSe single crystal, it shows a relatively low Tc8 K within the unusual nonmagnetic nematic phase below Ts90 K. It has been reported that the application of high pressure can induce a long-range antiferromagnetic order below Tm20 K at P1 GPa, and then achieve a high Tc37 K at P8 GPa. It rem
6、ains unclear how the high-Tc superconductivity is achieved in FeSe under pressure. In this regard, a detailed temperature-pressure phase diagram mapping out the exact relationship between the high-Tc superconductivity and the normal-state nematic order and the pressure-induced antiferromagnetic orde
7、r is indispensable for achieving a better understanding. By taking advantage of the cubic anvil cell apparatus that can maintain an excellent hydrostatic pressure condition up to 15 GPa, we recently undertook a comprehensive high-pressure magnetotransport study on high-quality FeSe single crystals a
8、nd obtained important results. In this article, we give a brief review on the recent progresses about the high-pressure studies of FeSe. By tracking the characteristic resistivity anomalies at the nematic order, the pressure-induced antiferromagnetic order, and the superconducting transition, we con
9、structed for FeSe a comprehensive temperature-pressure phase diagram, which depicts explicitly the detailed evolution of these competing electronic orders. We observed a dome-shaped antiferromagnetic phase boundary Tm (P) , and revealed the competitive relationship between these electronic orders. T
10、he superconducting Tc experiences two successive step increases at the critical pressures when the nematic order and the antiferromagnetic order are respectively suppressed, and finally the highest Tcmax=38.5 K is realized near Pc6 GPa when the antiferromagnetic order just collapses. We further meas
11、ured the Hall effect of FeSe to extract the electronic structure information under high pressure. Our Hall data show that the Fermi surface of FeSe in the normal state undergoes a reconstruction at P2 GPa, when the nematic order is suppressed and the antiferromagnetic order just emerges. The dominan
12、t charge carriers for the transport properties in the normal state change from the electron to the hole type. In addition, in the high-Tc phase near the optimal Tcmax at Pc6 GPa, the Hall coefficient experiences a dramatic enhancement and the magnetoresistance exhibits anomalous scaling behaviors, s
13、ignaling the presence of strongly enhanced inter-band spin fluctuations. These results suggest that the critical antiferromagnetic fluctuations play an important role for achieving the high-Tc superconductivity in FeSe. Aided by the first-principles calculations, we further confirmed that both elect
14、ron-like and hole-like Fermi surfaces are present in FeSe under high pressures, in favor of the Fermi surface nesting scenario as in the FeAs-based high-Tc superconductors. These above results on FeSe suggest great similarities with other FeAs-based superconductors, and thus constitute an important
15、step toward a unified understanding of iron-based superconductivity.Keyword： FeSe; high pressure magnetotransport measurements; unconventional superconductivity; magnetic quantum critical point; Received： 2017-06-28引用格式:孙建平, 王铂森, 程金光.Fe Se 单晶的高压研究进展.科学通报, 2017, 62:39253934Sun J P, Wang B S, Cheng J
16、G.Recent progress on the high-pressure studies of Fe Se single crystal (in Chinese) .Chin Sci Bull, 2017, 62:39253934, 自从 2008 年在 F 掺杂的 La OFe As 中报道了 Tc26 K 的高温超导电性1, 全球范围内掀起了继铜氧化物高温超导体之后新一轮的铁基高温超导研究热潮.人们通过稀土离子替代很快将其转变温度提升到 40 K 以上, 在高压下合成的 Sm O1-xFxFe As 的 Tc更是达到了 55 K5, 极大地促进了铁基超导体的研究.在铁基超导体系中, Fe Se 具有最简单的晶体结构, 却表现出诸多奇特反常的物理性质, 成为近年来的研究热点.随着温度降低, Fe Se 首先在 Ts90 K 发生了四方-正交结构相变, 形成具有各向异性电子结构的电子向列序, 造成图 1 所示的电阻率 (T) 曲线在 Ts处出现上翘6,7.但是, 与其他 F
