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Observation of Weak Anti-Localization and Electron-Electron Interaction on Few-Layer 1T′-MoTe2 Thin Films

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Chinese physics Letters 2018年第7期35卷 95-98页

作者：王钦于鹏黄祥威樊洁景秀年姬忠庆刘政刘广同杨昌黎吕力 Beijing National Laboratory for condensed matter physics Institute of PhysicsChinese Academy of Sciences University of Chinese Academy of Sciences School of materials Science and Engineering Nanyang Technological University Collaborative Innovation center of quantum matter

Electronic transports of few-layer 1T＇-MoTe2 films are measured at temperatures down to 0.26 K. The lowtemperature conductivity exhibits logarithmic temperature dependence and negative magneto response. The negative magnetoconductivity can be well fitted by the two-dimensional weak anti-localization theory taking a single channel of electrons into account, with the parameters α≈-0.5 and lφ∝ T-0 5. The logarithmic temperature dependence has a positive slope κ≈0.75, indicating the dominance of electron-electron interaction over the weak anti-localization effect, with an apparently negative Coulomb screening factor F that demands future work for clarification.

关键词： Electron-electron interactions

Observation of Temperature Induced Plasma Frequency Shift in an Extremely Large Magnetoresistance Compound LaSb

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Chinese physics Letters 2017年第7期34卷 271-274页

作者：班文静郭文婷雒建林王楠林 Institute of physics Chinese Academy of Sciences International center for quantum materials School of Physics Peking University Cavendish Laboratory Department of Physics University of Cambridge Collaborative Innovation center of quantum matter Beijing 100871 Collaborative Innovation center of quantum matter

We report an optical spectroscopy study on LaSb, a compound recently identified to exhibit extremely large magnetoresistance. Our optieal measurement indicates that the material has a low carrier density. More inter- estingly, the study reveals that the plasma frequency increases with decreasing temperature. This phenomenon suggests either an increase of the conducting carrier density or/and a decrease of the effective mass of carriers with decreasing temperature. We attribute it primarily to the latter effect. Two possible scenarios on its physical origin are examined and discussed. The study offers new insight into the electronic structure of this compound.

关键词： Observation of Temperature Induced Plasma Frequency Shift in an Extremely Large Magnetoresistance Compound LaSb

Dye-sensitized solar cells: Atomic scale investigation of interface structure and dynamics

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Chinese physics B 2014年第8期23卷 2-12页

作者：马薇张帆孟胜 Beijing National Laboratory for condensed matter physics and Institute of physics Chinese Academy of Sciences Collaborative Innovation center of quantum matter

Recent progress in dye-sensitized solar cells （DSC） research is reviewed, focusing on atomic-scale investigations of the interface electronic structures and dynamical processes, including the structure of dye adsorption onto Ti02, ultrafast electron injection, hot-electron injection, multiple-exciton generation, and electron-hole recombination. Advanced exper- imental techniques and theoretical approaches are briefly summarized, and then progressive achievements in photovoltaic device optimization based on insights from atomic scale investigations are introduced. Finally, some challenges and oppor- tunities for further improvement of dye solar cells are presented.

关键词： dye-sensitized solar cells interface structure absorption electron injection multiple-exciton generation charge recombination

Layer-by-layer epitaxy of multi-layer MoS2 wafers

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National Science Review 2022年第6期9卷 153-162页

作者： Qinqin Wang Jian Tang Xiaomei Li Jinpeng Tian Jing Liang Na Li Depeng Ji Lede Xian Yutuo Guo Lu Li Qinghua Zhang Yanbang Chu Zheng Wei Yanchong Zhao Luojun Du Hua Yu Xuedong Bai Lin Gu Kaihui Liu Wei Yang Rong Yang Dongxia Shi Guangyu Zhang Beijing National Laboratory for condensed matter physics and Institute of physics Chinese Academy of Sciences School of Physical Sciences University of Chinese Academy of Sciences Collaborative Innovation center of quantum matter and School of physics Peking University Songshan Lake materials Laboratory

The 2D semiconductor of MoS2has great potential for advanced electronics technologies beyond *** far, high-quality monolayer MoS2wafers have been available and various demonstrations from individual transistors to integrated circuits have also been shown. In addition to the monolayer, multilayers have narrower band gaps but improved carrier mobilities and current capacities over the ***, achieving high-quality multi-layer MoS2wafers remains a challenge. Here we report the growth of high-quality multi-layer Mo S2 4-inch wafers via the layer-by-layer epitaxy process. The epitaxy leads to well-defined stacking orders between adjacent epitaxial layers and offers a delicate control of layer numbers up to six. Systematic evaluations on the atomic structures and electronic properties were carried out for achieved wafers with different layer numbers. Significant improvements in device performances were found in thicker-layer field-effect transistors(FETs), as expected. For example, the average field-effect mobility(μFE) at room temperature(RT) can increase from ～80 cm~2·V-1·s-1for monolayers to ～110/145 cm~2·V-1·-1for bilayer/trilayer devices. The highest RT μFEof 234.7 cm~2·V-1·s-1and record-high on-current densities of 1.70 m A·μm-1at Vds= 2V were also achieved in trilayer MoS2FETs with a high on/off ratio of >107. Our work hence moves a step closer to practical applications of 2D MoS2in electronics.

关键词： 2D semiconductor multilayer MoS_2 wafer layer-by-layer epitaxy high performance transistors thin film transistors

Identifying the genes of unconventional high temperature superconductors

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Science Bulletin 2016年第7期61卷 561-569页

作者： Jiangping Hu Beijing National Laboratory for condensed matter physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China Collaborative Innovation center of quantum matter Beijing 100190 China

We elucidate a recently emergent framework in unifying the two families of high temperature （high To） superconductors, cuprates and iron-based superconductors. The unification suggests that the latter is simply the counterpart of the former to realize robust extended s-wave pairing symmetries in a square lattice. The unification identifies that the key ingredients （gene） of high Tc superconductors is a quasi two dimensional electronic environment in which the d-orbitals of cations that partic- ipate in strong in-plane couplings to the p-orbitals of anions are isolated near Fermi energy. With this gene, the superexchange magnetic interactions mediated by anions could maximize their contributions to superconductivity. Creating the gene requires special arrangements between local electronic structures and crystal lattice structures. The speciality explains why high Tc superconductors are so rare. An explicit prediction is made to realize high Tc superconductivity in Co/Ni-based materials with a quasi two dimensional hexagonal lattice structure formed by trigonal bipyramidal complexes.

关键词： Cuprates Iron-based superconductors Unconventional high Tc superconducotors Superexchange

Emergence of superconductivity from fully incoherent normal state in an iron-based superconductor (Ba_(0.6)K_(0.4))Fe_2As_2

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Science Bulletin 2019年第1期64卷 11-19页

作者： Jianwei Huang Lin Zhao Cong Li Qiang Gao Jing Liu Yong Hu Yu Xu Yongqing Cai Dingsong Wu Ying Ding Cheng Hu Huaxue Zhou Xiaoli Dong Guodong Liu Qingyan Wang Shenjin Zhang Zhimin Wang Fengfeng Zhang Feng Yang Qinjun Peng Zuyan Xu Chuangtian Chen Xingjiang Zhou Beijing National Laboratory for condensed matter physics Institute of Physics Chinese Academy of Sciences University of Chinese Academy of Sciences Technical Institute of physics and Chemistry Chinese Academy of Sciences Songshan Lake materials Laboratory Collaborative Innovation center of quantum matter

In unconventional superconductors, it is generally believed that understanding the physical properties of the normal state is a pre-requisite for understanding the superconductivity mechanism. In conventional superconductors like niobium or lead, the normal state is a Fermi liquid with a well-defined Fermi surface and well-defined quasipartcles along the Fermi surface. Superconductivity is realized in this case by the Fermi surface instability in the superconducting state and the formation and condensation of the electron pairs(Cooper pairing). The high temperature cuprate superconductors, on the other hand, represent another extreme case that superconductivity can be realized in the underdoped region where there is neither well-defined Fermi surface due to the pseudogap formation nor quasiparticles near the antinodal regions in the normal state. Here we report a novel scenario that superconductivity is realized in a system with well-defined Fermi surface but without quasiparticles along the Fermi surface in the normal *** resolution laser-based angle-resolved photoemission measurements have been performed on an optimally-doped iron-based superconductor(Ba_(0.6)K_(0.4))Fe_2As_2. We find that, while sharp superconducting coherence peaks emerge in the superconducting state on the hole-like Fermi surface sheets, no quasiparticle peak is present in the normal state. Its electronic behaviours deviate strongly from a Fermi liquid system. The superconducting gap of such a system exhibits an unusual temperature dependence that it is nearly a constant in the superconducting state and abruptly closes at Tc. These observations have provided a new platform to study unconventional superconductivity in a non-Fermi liquid system.

关键词： (Ba0.6K0.4)Fe2As2 ARPES Superconducting gap Normal state Non-Fermi liquid

Interface enhanced superconductivity in monolayer FeSe films on MgO(001):charge transfer with atomic substitution

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Science Bulletin 2018年第12期63卷 747-752页

作者： Guanyu Zhou Qinghua Zhang Fawei Zheng Ding Zhang Chong Liu Xiaoxiao Wang Can-Li Song Ke He Xu-Cun Ma Lin Gu Ping Zhang Lili Wang Qi-Kun Xue State Key Laboratory of Low-Dimensional quantum physics Department of PhysicsTsinghua UniversityBeijing 100084China Laboratory for Advanced materials&Electron Microscopy Beijing National Laboratory for Condensed Matter PhysicsInstitute of PhysicsChinese Academy of SciencesBeijing 100190China Institute of Applied physics and computational Mathematics Beijing 100088China Collaborative Innovation center of quantum matter Beijing 100084China

Interface enhanced superconductivity over 50 K has been discovered in monolayer Fe Se films grown on several TiO_2-terminated oxide *** such phenomenon exists in other oxide substrates remains an extremely interesting *** we report enhanced superconductivity with an onset transition temperature of 18 K in monolayer Fe Se on Mg O(001) substrate by transport *** transmission electron microscopy investigation on the interface structure indicates that Fe Se films grow epitaxially on Mg O(001) and that overlayer Fe atoms diffuse into the top two layers of Mg O and substitute Mg *** density functional theory calculations reveal that this substitution promotes the charge transfer from the Mg O substrate to the Fe Se films,an essential process that also occurs in monolayer Fe Se on TiO_2-terminated oxides and contributes to the enhanced superconductivity *** finding suggests that superconductivity enhancement in monolayer Fe Se films on oxides substrates is rather general as long as charge transfer is allowed at the interface,thus pointing out an explicit direction for searching for new high temperature superconductivity by interface engineering.

关键词： FeSe/MgO interface Interface superconductivity Transport measurement Scanning transmission electron microscopy

Exact solution of Heisenberg model with site-dependent exchange couplings and Dzyloshinsky–Moriya interaction

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Chinese physics B 2015年第10期24卷 460-466页

作者：杨丽君曹俊鹏杨文力 Beijing National Laboratory for condensed matter physics Institute of PhysicsChinese Academy of Sciences Collaborative Innovation center of quantum matter Institute of Modern physics Northwest University Beijing center for Mathematics and Information Interdisciplinary Sciences

We propose an integrable spin-1/2 Heisenberg model where the exchange couplings and Dzyloshinky-Moriya interactions are dependent on the sites. By employing the quantum inverse scattering method, we obtain the eigenvalues and the Bethe ansatz equation of the system with the periodic boundary condition. Furthermore, we obtain the exact solution and study the boundary effect of the system with the anti-periodic boundary condition via the off-diagonal Bethe ansatz. The operator identities of the transfer matrix at the inhomogeneous points are proved at the operator level. We construct the T -Q relation based on them. From which, we obtain the energy spectrum of the system. The corresponding eigenstates are also constructed. We find an interesting coherence state that is induced by the topological boundary.

关键词： Bethe ansatz Yang-Baxter equation T-Q relation

Transparent conductive reduced graphene oxide thin films produced by spray coating

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Science China(physics,Mechanics & Astronomy) 2015年第1期58卷 42-46页

作者： SHI HongFei WANG Can SUN ZhiPei ZHOU YueLiang JIN KuiJuan YANG GuoZhen Beijing National Laboratory for condensed matter physics Institute of Physics Chinese Academy of Sciences Department of Micro- and Nanosciences Aalto University Collaborative Innovation center of quantum matter

Reduced graphene oxide thin films were fabricated on quartz by spray coating method using a stable dispersion of reduced graphene oxide in N,*** dispersion was produced by chemical reduction of graphene oxide,and the film thickness was controlled with the amount of spray *** measurements revealed that the thin films have near-atomically flat *** chemical and structural parameters of the samples were analyzed by Raman and XPS *** was found that the thin films show electrical conductivity with good optical transparency in the visible to near infrared *** sheet resistance of the films can be significantly reduced by annealing in vacuum and reach 58 k?with a light transmittance of 68.69%at 550 *** conductive transparent properties of the reduced graphene oxide thin films would be useful to develop flexible electronics.

关键词： reduced graphene oxide transparent conductive film spray coating