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Observation of multiple charge density wave phases in epitaxial monolayer 1T-VSe_(2) film

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Chinese Physics B 2022年第10期31卷 137-145页

作者： Junyu Zong Yang Xie Qinghao Meng Qichao Tian Wang Chen Xuedong Xie Shaoen Jin Yongheng Zhang Li Wang Wei Ren Jian Shen Aixi Chen Pengdong Wang Fang-Sen Li Zhaoyang Dong Can Wang Jian-Xin Li Yi Zhang National Laboratory of Solid State Microstructure School of PhysicsNanjing UniversityNanjing 210093China Vacuum Interconnected Nanotech Workstation(Nano-X) Suzhou Institute of Nano-Tech and Nano-Bionics(SINANO)Chinese Academy of SciencesSuzhou 215123China Department of Applied Physics Nanjing University of Science and TechnologyNanjing 210094China Collaborative Innovation Center of Advanced Microstructures Nanjing UniversityNanjing 210093China

As a special order of electronic correlation induced by spatial modulation, the charge density wave(CDW) phenomena in condensed matters attract enormous research interests. Here, using scanning-tunneling microscopy in various temperatures, we discover a hidden incommensurate stripe-like CDW order besides the(■) CDW phase at low-temperature of 4 K in the epitaxial monolayer 1T-VSe_(2) film. Combining the variable-temperature angle-resolved photoemission spectroscopic(ARPES) measurements, we discover a two-step transition of an anisotropic CDW gap structure that consists of two parts △_(1) and△_(2). The gap part ?1 that closes around ~ 150 K is accompanied with the vanish of the(√7×√3) CDW phase. While another momentum-dependent gap part △_(2) can survive up to ~ 340 K, and is suggested to the result of the incommensurate CDW phase. This two-step transition with anisotropic gap opening and the resulted evolution in ARPES spectra are corroborated by our theoretical calculation based on a phenomenological form for the self-energy containing a two-gap structure △_(1) +△_(2), which suggests different forming mechanisms between the(√7×√3) and the incommensurate CDW phases. Our findings provide significant information and deep understandings on the CDW phases in monolayer 1T-VSe_(2) film as a two-dimensional(2D) material.

关键词： charge density waves VSe_(2) band structures STM ARPES

Transport and Capacitance Properties of charge density Wave in Few-Layer 2H-TaS2 Devices

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Chinese Physics Letters 2014年第7期31卷 164-167页

作者：曹玉飞蔡凯明黎丽君鲁文建孙玉平王开友 The State Key Laboratory of Superlattices and Mierostructure Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 Key Laboratory of Materials Physics Institute of Solid State Physics Chinese Academy of Sciences Hefei 230031

We carefully investigate the transport and capacitance properties of few layer charge density wave （CDW） 2HTaS2 devices. The CDW transition temperature and the threshold voltage vary from device to device, which is attributed to the interlayer interaction and inhomogeneous local defects of these micro-devices based on few layer 2H-TaS2 flakes. The nonlinear rather than linear current voltage characteristic of 2H-TaS2 devices is observed in our experiment at low temperature. The temperature dependence of the relative threshold voltage can be scaled to （1 - T /Tr ）^0.5＋δ with δ = 0.08 for the different measured devices with the presence of the CDWs. The conductance-voltage and capacity-voltage measurements are performed simultaneously. At very low ac active voltage, we find that the hysteresis loops of these two measurements exactly match each other. Our results point out that the capacity-voltage measurements can also be used to define the threshold depinning voltage of the CDW, which gives us a new method to investigate the CDWs.

关键词： charge density waves THRESHOLD voltage TRANSITION temperature HYSTERESIS loop CURRENT-voltage characteristics

Extremely low-energy collective modes in a quasi-one-dimensional topological system

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Science China(Physics,Mechanics & Astronomy) 2022年第5期65卷 90-96页

作者： Zhengxin Wei Shuai Zhang Yulun Su Liang Cheng Haidong Zhou Zhigang Jiang Hongming Weng Jingbo Qi State Key Laboratory of Electronic Thin Films and Integrated Devices University of Electronic Science and Technology of ChinaChengdu 610054China Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China Department of Physics and Astronomy University of TennesseeKnoxvilleTennessee 37996USA School of Physics Georgia Institute of TechnologyAtlantaGeorgia 30332USA

We have investigated the quasiparticle dynamics and collective excitations in the quasi-one-dimensional material ZrTe_(5) using ultrafast optical pump-probe *** time-domain results reveal two coherent oscillations having extremely low energies of hω_(1)~0.33 me V(0.08 THz)and hω_(2)-1.9 me V(0.45 THz),which are softened as the temperature approaches two different critical temperatures(~54 K and~135 K).We attribute these two collective excitations to the amplitude mode of photoinduced dynamic charge density waves in ZrTe_(5) with tremendously small nesting wave ***,a peculiar quasiparticle decay process associated with the hω_(2) mode with a timescale of~1-2 ps is found below the transition temperature T*(~135 K).Our findings provide pivotal information for studying the fluctuating order parameters and their associated quasiparticle dynamics in various low-dimensional topological systems and other materials.

关键词： charge density waves ultrafast quasiparticle dynamics amplitude mode

Mean—Field Calculations for the Three—Dimensional Holstein Model

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Chinese Physics Letters 2002年第8期19卷 1184-1186页

作者：罗强刘川 SchoolofPhysics PekingUniversityBeijing100871

The electron-phonon Holstein model is studied in three spatial dimensions. It is argued that this model can be used to account formajor features of the high-TcBaPb1-xBixO3and BaxK1-xBiO3systems. Mean-field calculations are performed via a path integral representation of the model. charge-density-waveorder parameters and transition temperatures are obtained.

关键词： charge density waves

The Edge Magnetization and Strip Phase of Graphene Quantum Dots with Long-Range Coulomb Interaction

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Chinese Physics Letters 2014年第4期31卷 150-154页

作者： LINing ZHU Wen-Huan LIANG Qi DING Guo-Hui Instrumental Analysis Center Shanghai Jiao Tong University Shanghai 200240 Key Laboratory of Artificial Structures and Quantum Control (Ministry of Bducation) Department of Physics and Astronomy Shanghai Jiao Tong University Shanghai 200240

We investigate the magnetism and optical absorption properties of charge neutral hexagonal graphene quantum dots （GODs） terminated with zigzag edges by using a tight-binding Hubbard type model for the 7r electrons. Within the Hartree Fock approximation and taking into account the long-range Coulomb interaction, our cal- culation yields a ferromagnetic ground state with magnetic moments localized on the edges for GODs, and also gives an antiferromagnetism state with the energy very c/ose to the ferromagnetism ground state. We find that both the ferromagnetic and the antiferrornagnetic states have stripe patterned charge density distributions as a result of the long-range Coulomb interaction. The optical conductivity for GQDs has an energy gap in the low frequency regime in contrast to the bulk neutral graphene sheet where a universal constant is approached.

关键词： MAGNETIZATION GRAPHENE QUANTUM dots COULOMB'S law FERROMAGNETISM charge density waves

Titanium doped kagome superconductor CsV_(3-x)Ti_(x)Sb_(5)and two distinct phases

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Science Bulletin 2022年第21期67卷 2176-2185页

作者： Haitao Yang Zihao Huang Yuhang Zhang Zhen Zhao Jinan Shi Hailan Luo Lin Zhao Guojian Qian Hengxin Tan Bin Hu Ke Zhu Zouyouwei Lu Hua Zhang Jianping Sun Jinguang Cheng Chengmin Shen Xiao Lin Binghai Yan Xingjiang Zhou Ziqiang Wang Stephen J.Pennycook Hui Chen Xiaoli Dong Wu Zhou Hong-Jun Gao Beijing National Center for Condensed Matter Physics and Institute of Physics Chinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100190China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of SciencesBeijing 100190China Department of Condensed Matter Physics Weizmann Institute of ScienceRehovot 7610001Israel Department of Physics Boston CollegeChestnut HillMA 02467USA

The vanadium-based kagome superconductor CsV_(3)Sb_(5) has attracted tremendous attention due to its unexcepted anomalous Hall effect(AHE),charge density waves(CDWs),nematicity,and a pseudogap pair density wave(PDW)coexisting with unconventional strong-coupling *** origins of CDWs,unconventional superconductivity,and their correlation with different electronic states in this kagome system are of great significance,but so far,are still under *** doping in the kagome layer provides one of the most direct ways to reveal the intrinsic physics,but remains ***,we report,for the first time,the synthesis of Ti-substituted CsV_(3)Sb_(5) single crystals and its rich phase diagram mapping the evolution of intertwining electronic *** Ti atoms directly substitute for V in the kagome ***_(3-x)Ti_(x)Sb_(5) shows two distinct superconductivity phases upon *** Ti slightly-substituted phase displays an unconventional V-shaped superconductivity gap,coexisting with weakening CDW,PDW,AHE,and *** Ti highly-substituted phase has a U-shaped superconductivity gap concomitant with a short-range rotation symmetry breaking CDW,while long-range CDW,twofold symmetry of in-plane resistivity,AHE,and PDW are ***,we also demonstrate the chemical substitution of V atoms with other elements such as Cr and Nb,showing a different modulation on the superconductivity phases and *** findings open up a way to synthesise a new family of doped CsV_(3)Sb_(5) materials,and further represent a new platform for tuning the different correlated electronic states and superconducting pairing in kagome superconductors.

关键词： Kagome superconductor Chemical doping charge density waves Nematicity Competing orders