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Direct observation of nodeless superconductivity and phonon modes in electron-doped copper oxide Sr1-XNdXCuO2

National Science Review 2022年第4期9卷 76-83页

作者： Jia-Qi Fan Xue-Qing Yu Fang-Jun Cheng Heng Wang Ruifeng Wang Xiaobing Ma Xiao-Peng Hu Ding Zhang Xu-Cun Ma Qi-Kun Xue Can-Li Song State Key Laboratory of Low-Dimensional Quantum Physics Department of PhysicsTsinghua University Frontier Science Center for Quantum Information Beijing Academy of Quantum Information Sciences RIKEN Center for Emergent Matter Science (CEMS) Southern University of Science and Technology

The microscopic understanding of high-temperature superconductivity in cuprates has been hindered by the apparent complexity of crystal structures in these materials.We used scanning tunneling microscopy and spectroscopy to study the electron-doped copper oxide compound Sr1-xNdxCuO2,which has only bare cations separating the CuO2planes and thus the simplest infinite-layer structure of all cuprate superconductors.Tunneling conductance spectra of the major CuO2planes in the superconducting state reve aled direct evidence for a nodeless pairing gap,regardless of variation of its magnitude with the local doping of trivalent neodymium.Furthermore,three distinct bosonic modes are observed as multiple peak-dip-hump features outside the superconducting gaps and their respective energies depend little on the spatially varying gaps.As well as the bosonic modes,with energies identical to those of the external,bending and stretching phonons of copper oxides,our findings reveal the origin of the bosonic modes in lattice vibrations rather than spin excitations.

关键词： nodeless superconductivity phonon modes cuprate superconductors CuO2 plane

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Correlate phonon modes with ion transport via isotope substitution

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Science China Chemistry 2023年第3期66卷 768-777页

作者： Yirong Gao Jianxing Huang Jun Cheng Shou-Hang Bo University of Michigan–Shanghai Jiao Tong University Joint Institute Shanghai Jiao Tong UniversityShanghai 200240China State Key Laboratory of Physical Chemistry of Solid Surface iChEMCollege of Chemistry and Chemical EngineeringXiamen UniversityXiamen 361005China Solid-State Battery Research Center Global Institute of Future TechnologyShanghai Jiao Tong UniversityShanghai 200240China School of Chemistry and Chemical Engineering Shanghai Jiao Tong UniversityShanghai 200240China

Understanding the correlations between lattice dynamics(phonons) and ion transport is important for improving the ionic conductivity of solid-state electrolytes. This understanding largely hinges on selective tuning or excitation of specific phonon modes without changing the chemical environments of atoms, which is, however, challenging to be achieved. In this work, we used ~6Li isotope substitution to selectively change the phonon properties associated with lithium, without introducing additional defects or disorders which would affect the ion transport properties. The changes in the phonon modes were then related to ion transport properties through impedance measurements and deep potential molecular dynamics simulations. Our results demonstrated that lower lithium vibration frequency leads to higher ionic conductivity and lower activation energy in the garnet solid-state electrolyte of Li_(6.4)La_(3)Zr_(1.4)Ta_(0.6)O_(12). We furthermore quantified the effect of lithium-related phonons on the migration entropy and attempt frequency, which would be difficult to be achieved otherwise. Our work suggests an effective isotope substitution method to decouple the effect of phonon modes to ion transport from that of other complex structural factors. The obtained insights can contribute to innovative understanding of ion transport in solids and strategies to optimize the ionic conductivity of solid-state electrolytes.

关键词： solid-state electrolytes phonon modes ion transport isotope substitution lattice dynamics

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新型二维半导体TeSe_2:间接带隙到直接带隙的转变（英文）

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Science China Materials 2017年第8期60卷 747-754页

作者：吴伯朝尹久仁丁燕怀张平 Institute of Rheological Mechanics Xiangtan University College of Civil Engineering & Mechanics Xiangtan University

本文基于第一性原理计算预测了一种新颖的二维稳定结构TeSe_2,结果显示单层TeSe_2是一种半导体材料,其带隙值为2.392 e V.有趣的是单层TeSe_2的间接能带在宽范围的双向负应变(0.02~0.12)作用下转变为直接能带.比单层黑磷烯更小的有效空... 详细信息

本文基于第一性原理计算预测了一种新颖的二维稳定结构TeSe_2,结果显示单层TeSe_2是一种半导体材料,其带隙值为2.392 e V.有趣的是单层TeSe_2的间接能带在宽范围的双向负应变(0.02~0.12)作用下转变为直接能带.比单层黑磷烯更小的有效空穴电子质量预示了TeSe_2具有更高的载流子迁移速率.此外,对不同厚度TeSe_2的声子模及光学性质也进行了计算,结果显示不同厚度的TeSe_2具有较强的光学各向异性,尤其是多层TeSe_2具有更宽的吸收波长.这些结果表明,TeSe_2作为一种新颖的二维结构在纳米器件领域具有巨大的应用潜力,如高速超薄晶体管,纳米力学传感器,紫外–可见红光区声光偏振器及光电子器件等.

关键词： Te Se2 first-principles calculations direct band gap phonon modes optical absorption

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