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| 1 | A vacuum ultraviolet laser with a submicrometer spot for spatially resolved photoemission spectroscopy显示文摘Vacuum ultraviolet(VUV)lasers have demonstrated great potential as the light source for various spectroscopies,which,if they can be focused into a small beam spot,will not only allow investigation of mesoscopic materials and structures but also find application in the manufacture of nano-objects with excellent precision.In this work,we report the construction of a 177 nm VUV laser that can achieve a record-small(〜0.76 μm)focal spot at a long focal length(~45 mm)by using a flat lens without spherical aberration.The size of the beam spot of this VUV laser was tested using a metal grating and exfoliated graphene flakes,and we demonstrated its application in a fluorescence spectroscopy study on pure and Tm3+-doped NaYF4 microcrystals,revealing a new emission band that cannot be observed in the traditional up-conversion process.In addition,this laser system would be an ideal light source for spatially and angleresolved photoemission spectroscopy. | Yuanhao Mao Dong Zhao Shen Yan Hongjia Zhang Juan Li Kai Han Xiaojun Xu Chuan Guo Lexian Yang Chaofan Zhang Kun Huang Yulin Chen | 2021 | Light(Science & Applications)2021，10，3： | 3 |
| 2 | Visualization of the electronic phase separation in superconducting K_(x)Fe_(2−y)Se_(2)显示文摘Type-II iron-based superconductors(Fe-SCs),the alkali-metal-intercalated iron selenide A_(x)Fe_(2−y)Se_(2)(A=K,Tl,Rb,etc.)with a superconducting transition temperature of 32 K,exhibit unique properties such as high Néel temperature,Fe-vacancies ordering,antiferromagnetically ordered insulating state in the phase diagram,and mesoscopic phase separation in the superconducting materials.In particular,the electronic and structural phase separation in these systems has attracted intensive attention since it provides a platform to unveil the insulating parent phase of type-II Fe-SCs that mimics the Mott parent phase in cuprates.In this work,we use spatial-and angle-resolved photoemission spectroscopy to study the electronic structure of superconducting K_(x)Fe_(2−y)Se_(2).We observe clear electronic phase separation of K_(x)Fe_(2−y)Se_(2) into metallic islands and insulating matrix,showing different K and Fe concentrations.While the metallic islands show strongly dispersive bands near the Fermi level,the insulating phase shows an energy gap up to 700 meV and a nearly flat band around 700 meV below the Fermi energy,consistent with previous experimental and theoretical results on the superconducting K_(1−x)Fe_(2)Se_(2)(122 phase)and Fe-vacancy ordered K_(0.8)Fe_(1.6)Se_(2)(245 phase),respectively.Our results not only provide important insights into the mysterious composition of phase-separated superconducting and insulating phases of K_(x)Fe_(2−y)Se_(2),but also present their intrinsic electronic structures,which will shed light on the comprehension of the unique physics in type-II Fe-SCs. | Yujie Chen Juan Jiang Haifeng Yang Pavel Dudin Alexey Barinov Zhongkai Liu Haihu Wen Lexian Yang Yulin Chen | 2021 | Nano Research2021，14，3： | 1 |
| 3 | ARPES investigation of the electronic structure and its evolution in magnetic topological insulator MnBi_(2+2n)Te_(4+3n)family显示文摘In the past 5 years,there has been significant research interest in the intrinsic magnetic topological insulator family compounds MnBi_(2+2n)Te_(4+3n)n(where n=0,1,2…).In particular,exfoliated thin films of MnBi_(2)Te_(4)have led to numerous experimental breakthroughs,such as the quantum anomalous Hall effect,axion insulator phase and high-Chern number quantum Hall effect without Landau levels.However,despite extensive efforts,the energy gap of the topological surface states due to exchange magnetic coupling,which is a key feature of the characteristic band structure of the system,remains experimentally elusive.The electronic structure measured by using angle-resolved photoemission(ARPES)shows significant deviation from ab initio prediction and scanning tunneling spectroscopy measurements,making it challenging to understand the transport results based on the electronic structure.This paper reviews the measurements of the band structure of MnBi_(2+2n)Te_(4+3n)n magnetic topological insulators using ARPES,focusing on the evolution of their electronic structures with temperature,surface and bulk doping and film thickness.The aim of the review is to construct a unified picture of the electronic structure of MnBi_(2+2n)Te_(4+3n)n compounds and explore possible control of their topological properties. | Runzhe Xu Lixuan Xu Zhongkai Liu Lexian Yang Yulin Chen | 2024 | National Science Review2024，11，2： | 0 |
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