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Science Bulletin 2016年第14期61卷 1126-1131页

作者： Haipeng Wang Zirong Ye Yan Zhang Nanlin Wang Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of SciencesBeijing 100190 China International Center for Quantum Materials School of PhysicsPeking University Beijing 100871 China Collaborative Innovation Center of Quantum Matter Beijing 100871 China

We perform an in-plane optical spectroscopy measurement on high quality FeSe single crystals grown by a vapor transport technique. Below the structural transition at Ts - 90 K, the reflectivity spectrum clearly shows a gradual suppression around 400 cm-1 and the conductivity spectrum shows a peak at higher frequency. The energy scale of this gap-like feature is comparable to the width of the band splitting observed by ARPES. The low-frequency conductivity consists of two Drude components and the overall plasma frequency is smaller than that of the FeAs based compounds, suggesting a lower cartier density or stronger correlation effect. The plasma frequency becomes even smaller below Ts which agrees with the very small Fermi energy estimated by other experiments. Similar to iron pnictides, a clear temperature-induced spectral weight transfer is observed for FeSe, being indicative of strong correlation effect.

关键词： Iron-based superconductor Opticalspectroscopy Nematic phase band reconstruction

Optical study of magnetic topological insulator MnBi_(4)Te_7

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Chinese Physics B 2024年第1期33卷 231-235页

作者：廖知裕沈冰邱祥冈许兵 Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100049China State Key Laboratory of Optoelectronic Materials and Technologies School of PhysicsSun Yat-Sen UniversityGuangzhou 510275China Songshan Lake Materials Laboratory Dongguan 523808China

We present an infrared spectroscopy study of the magnetic topological insulator MnBi_(4)Te_7 with antiferromagnetic(AFM) order below the Neel temperature TN= 13 K. Our investigation reveals that the low-frequency optical conductivity consists of two Drude peaks, indicating a response of free carriers involving multiple bands. Interestingly, the narrow Drude peak grows strongly as the temperature decreases, while the broad Drude peak remains relatively unchanged. The onset of interband transitions starts around 2000 cm^(-1), followed by two prominent absorption peaks around 10000 cm^(-1) and 20000 cm^(-1). Upon cooling, there is a notable transfer of spectral weight from the interband transitions to the Drude response. Below TN, the AFM transition gives rise to small anomalies of the charge response due to a band *** findings provide valuable insights into the interplay between magnetism and the electronic properties in MnBi_(4)Te_7.

关键词： infrared spectroscopy magnetic topological insulator Drude model band reconstruction

Optical spectrum of ferrovalley materials:A case study of Janus H-VSSe

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Chinese Physics B 2024年第1期33卷 54-59页

作者：罗朝波刘文超彭向阳 Hunan Key Laboratory for Micro-Nano Energy Materials and Devices School of Physics and OptoelectronicsXiangtan UniversityXiangtan 411105China

As opposed to the prototypical MoS2 with centroasymmetry,Janus ferrovalley materials such as H-VSSe are less symmetric with the mirror symmetry and time reversal symmetry broken,and hence possess spontaneous valley polarization and strong *** optical transition is an important means to excite the valley *** investigate the optical spectrum of H-VSSe by using the many-body perturbation-based GW approach and solving the Bethe–Salpeter equation(BSE)to include the electron–hole *** is found that after the GW correction,the band gaps of the quasiparticle bands are much larger than those obtained by the normal density functional *** system is ferromagnetic and the valley gaps become non-degenerate due to spin–orbit coupling(SOC).The position of the lowest BSE peak is much lower than the quasiparticle band gap,indicating that the excitonic effect is *** peak is split into two peaks by the *** binding energy difference between these two BSE peaks is about the same as the difference between the inequivalent valley *** results show that in Janus H-VSSe the two lowest exciton peaks are from the two inequivalent valleys with different gaps,in contrast to the A and B exciton peaks of MoS2 which are from the same valley.

关键词： infrared spectroscopy magnetic topological insulator Drude model band reconstruction

Electronic origin of the enhanced thermoelectric efficiency of CuSe

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Science Bulletin 2020年第22期65卷 1888-1893,M0003页

作者： Shucui Sun Yiwei Li Yujie Chen Xiang Xu Lu Kang Jingsong Zhou Wei Xia Shuai Liu Meixiao Wang Juan Jiang Aiji Liang Ding Pei Kunpeng Zhao Pengfei Qiu Xun Shi Lidong Chen Yanfeng Guo Zhengguo Wang Yan Zhang Zhongkai Liu Lexian Yang Yulin Chen State Key Laboratory of Low Dimensional Quantum Physics Department of PhysicsTsinghua UniversityBeijing 100084China Department of Physics Clarendon LaboratoryUniversity of OxfordOxford OX13PUUK School of Physical Science and Technology ShanghaiTech UniversityShanghai 201210China State Key Laboratory of High Performance Ceramics and Superfine Microstructure Shanghai Institute of CeramicsChinese Academy of SciencesShanghai 200050China International Center for Quantum Materials School of PhysicsPeking UniversityBeijing 100871China ShanghaiTech Laboratory for Topological Physics Shanghai 200031China Frontier Science Center for Quantum Information Beijing 100084China

Thermoelectric materials(TMs)can uniquely convert waste heat into electricity,which provides a potential solution for the global energy crisis that is increasingly *** Cu2Se,with ionic conductivity of Cu ions,exhibits a significant enhancement of its thermoelectric figure of merit z T by a factor of^3 near its structural transition around 400 ***,we show a systematic study of the electronic structure of Cu2Se and its temperature evolution using high-resolution angle-resolved photoemission *** heating across the structural transition,the electronic states near the corner of the Brillouin zone gradually disappear,while the bands near the centre of Brillouin zone shift abruptly towards high binding energies and develop an energy ***,the observed band reconstruction well reproduces the temperature evolution of the Seebeck coefficient of Cu2 Se,providing an electronic origin for the drastic enhancement of the thermoelectric performance near 400 *** current results not only bridge among structural phase transition,electronic structures and thermoelectric properties in a condensed matter system,but also provide valuable insights into the search and design of new generation of thermoelectric materials.

关键词： Thermoelectric materials Cu2Se Angle-resolved photoemission spectroscopy Seebeck coefficient band reconstruction