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Oxides for high temperature superconductivity and Beyond

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Tsinghua Science and Technology 1998年第1期3卷 57-78页

作者： Ching Wu Chu Department of Physics and Texas Center for superconductivity, University of Houston, Houston, TX 77204, USA Department of Physics and Texas Center for superconductivity University of Houston TX 77204 USA

In this paper, I shall briefly summarize the present state of high temperature superconductivity research and development together with an assessment of the prospect of yet a higher transition temperature and an outline of challenges facing today's practitioners of high temperature super conductivity science and technology. The extensive knowledge acquired in the last decade in high temperature superconducting science and materials may usher in a new era of material engineering, which I would like to call mesomaterial engineering for the fabrication of perovskite and related oxide superlattices, a new class of materials for science and technology. Therefore, I shall also present the rationale behind this effort and the promises of the new materials, together with a list of several preliminary successful examples.

关键词： high temperature superconductivity oxide mesomaterial engineering

high-temperature interface superconductivity in bilayer copper oxide films by pulsed laser deposition

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Science China Materials 2020年第1期63卷 128-135页

作者： Jia-hao Deng Tian-shuang Ren Le-le Ju Hong-rui Zhang Ji-rong Sun Bao-gen Shen Yan-wu Xie Interdisciplinary Center of Quantum Information Zhejiang Province Key Laboratory of Quantum Technology and Deviceand Department of PhysicsZhejiang UniversityHangzhou 310027China Beijing National Laboratory for Condensed Matter Physics&Institute of Physics Chinese Academy of SciencesBeijing 100190China Collaborative Innovation Center of Advanced Microstructures Nanjing UniversityNanjing 210093China

In a seminal work, Gozar et al. reported on the high-temperature interface superconductivity in bilayers of insulating La2Cu O4 and metallic La2-xSrxCuO4(x=0.45). An interesting question to address is how general and robust this interface superconductivity is. In the past, the cuprate bilayers were grown in a unique atomic-layer molecular beam epitaxy system, with a Sr doping range of x≤0.47, and the atomically flat interface was thought to be indispensable. Here, we have fabricated bilayers of La2CuO4 and La2-xSrxCuO4 by pulsed laser deposition. We have tried to extend the nominal doping range of Sr from the previous maximum of 0.47 to the present1.70(the nominal Sr content in the targets). X-ray diffraction result indicates that our La2-xSrxCuO4 films with x≤0.60 have very high crystalline quality;but the film crystalline structure degrades gradually with further increasing x, and finally the structure is fully lost when x reaches 1.40 and higher. Although the film quality scatters dramatically, our experiments show that there exists superconductivity for bilayers in nearly the entire over-doped Sr range, except for a non-superconducting region at x^0.80. These observations demonstrate that the interface superconductivity in copper oxides is very general and robust.

关键词： cuprate superconductivity interface pulsed laser deposition high temperature superconductivity

Nonlocal Theory of high-temperature superconductivity

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Journal of Modern Physics 2021年第5期12卷 552-593页

作者： Boris V. Alexeev MIREA—Russian State Technological University Moscow Russia

The Boltzmann local physical kinetics forecasts the destruction of SC regime because of the heat movement of particles. Then, the most fundamental distinction between a strange metal and a conventional metal is the absence of well-defined quasi-particles. Here, we show that the mentioned “quasi-particles” are solitons, which are formed as a result of self-organization of ionized matter. Shortcomings of the Boltzmann physical kinetics consist in the local description of the transport processes on the level of infinitely small physical volumes as elements of diagnostics. The non-local physics leads to the theory superconductivity including the high temperature diapason. The generalized non-local non-stationary London’s formula is derived.

关键词： high temperature superconductivity Generalized London’s Formula Nonlocal Physics Transport Processes in Superconductors Longitudinal Electromagnetic Waves Solitons in Superconductors

In-situ spectroscopic studies and interfacial engineering on FeSe/oxide heterostructures: Insights on the interfacial superconductivity

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Chinese Physics B 2015年第11期24卷 30-42页

作者：彭瑞徐海超封东来 State Key Laboratory of Surface Physics Department of Physics Fudan University Advanced Materials Laboratory Fudan University

The discovery of high temperature superconductivity in single-layer FeSe/SrTiO3 provides a new platform for ex- ploring superconductivity and pursuing higher Tc （superconducting transition temperature） through fabricating artificial heterostructures. In this paper, we review the recent progress in studying and tuning the interfacial superconductivity in single-layer FeSe, through the combined in-situ spectroscopic studies and atomic-scale engineering. By fabricating arti- ficial heterostructures, various interfacial factors were tuned, and the corresponding evolutions of electronic structure and superconducting gap behavior were investigated. These studies enrich the current understanding on the interfacial superconductivity, and provide clues for further enhancing Tc through interface engineering.

关键词： single-layer FeSe high temperature superconductivity interface spectroscopic study

superconductivity in the cuprates： Deduction of mechanism for d-wave pairing through analysis of ARPES

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Frontiers of physics 2011年第4期6卷 440-449页

作者： Han-Yong Choi Chandra M. Varma Xing-jiang Zhou Department of Physics and Institute for Basic Science Research Sung Kyun Kwan University Suwon 440-746 Korea Department of Physics and Astronomy University of California Riverside California 92521 USA National Laboratory for superconductivity Institute of Physics Chinese Academy of Sciences Beijing 100190 China

In the Eliashberg integral equations for d-wave superconductivity, two different functions （α2F）n（ω, θ） and （α2F）p,d（ω） determine, respectively, the ＂normal＂ self-energy and the ＂pairing＂ self-energy, w is the frequency of fluctuations scattering the fermions whose momentum is near the Fermi-surface and makes an angle θ to a chosen axis. We present a quantitative analysis of the high-resolution laser based Angle Resolved Photoemission Spectroscopy （ARPES） data on a slightly under doped cuprate compound Bi2212 and use the Eliashberg equations to deduce the w and dependence of （α2F）n（ω, θ） for T just above Tc and below Tc. Besides its detailed w dependence, we find the remarkable result that this function is nearly independent of θ between the （π; π）-direction and 25 degrees from it, except for the dependence of the cut-off energy on 8. Assuming that the same fluctuations determine both the normal and the pairing self-energy, we ask what theories give the function （α2F）p,d（ω） required for the d-wave pairing instability at high temperatures as well as the deduced （α2F）n（θ, w）. We show that the deduced （α2F）n（θ, w） can only be obtained from antiferromagnetic （AFM） fluctuations if their correlation length is smaller than a lattice constant. Using （α2F）p,d（W） consistent with such a correlation length and the symmetry of matrix-elements scatter- ing fermions by AFM fluctuations, we calculate Tc and show that AFM fluctuations are excluded as the pairing mechanism for d-wave superconductivity in cuprates. We also consider the quantumcritical fluctuations derived microscopically as the fluctuations of the observed loop-current order discovered in the under-doped cuprates, and which lead to the marginal Fermi-liquid properties in the normal state. We show that their frequency dependence and the momentum dependence of their matrix-elements to scatter fermions are consistent with the θ and w dependence of the deduced （α2F）n（ω, θ）. The pairing kernel （α2F）p,d（W） calculated using

关键词： high temperature superconductivity mechanisms of superconductivity

What makes the Tc of monolayer FeSe on SrTiO3 so high： a sign-problem-free quantum Monte Carlo study

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Science Bulletin 2016年第12期61卷 925-930页

作者： Zi-Xiang Li Fa Wang Hong Yao Dung-Hai Lee Institute for Advanced Study Tsinghua UniversityBeijing 100084China International Center for Quantum Materials School of PhysicsPeking UniversityBeijing 100871China Collaborative Innovation Center of Quantum Matter Beijing 100871China Department of Physics University of CaliforniaBerkeleyCA 94720USA Materials Sciences Division Lawrence Berkeley National LaboratoryBerkeleyCA 94720USA

Monolayer FeSe films grown on SrTiO_3(STO)substrate show superconducting gap-opening temperatures(T_c) which are almost an order of magnitude higher than those of the bulk FeSe and are highest among all known Fe-based superconductors. Angle-resolved photoemission spectroscopy observed ‘‘replica bands' ' suggesting the importance of the interaction between FeSe electrons and STO phonons. These facts rejuvenated the quest for T_c enhancement mechanisms in iron-based, especially ironchalcogenide, superconductors. Here, we perform the first numerically-exact sign-problem-free quantum Monte Carlo simulations to iron-based superconductors. We(1) study the electronic pairing mechanism intrinsic to heavily electron doped FeSe films, and(2) examine the effects of electron–phonon interaction between FeSe and STO as well as nematic fluctuations on T_c. Armed with these results, we return to the question ‘‘what makes the Tcof monolayer FeSe on SrTiO_3 so high?'' in the conclusion and discussions.

关键词： high temperature superconductivity Pairing mechanism Iron-based superconductivity FeSe/STO Sign-problem-free quantum Monte-Carlosimulation

What makes the T_c of FeSe/SrTiO_3 so high?

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Chinese Physics B 2015年第11期24卷 23-29页

作者： Dung-Hai Lee Department of Physics University of California at Berkeley Material Science Division Lawrence Berkeley National Laboratory

This paper reviews some of the recent progresses in the study of high temperature superconductivity in the interface between a single unit cell FeSe and SrTiO3. It offers the author＇s personal view of why Tc is high ... 详细信息

关键词： high temperature superconductivity

The normal state of high temperature oxide superconductor——Pseudogapped metallic state

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Science China Mathematics 2001年第3期44卷 389-395页

作者：章立源冯小兵 Department of Physics Peking University Beijing 100871 China Dalian Railway Institute Dalian 116028 China

Looking back on the experiments about the normal state of the high temperature superconductor (NTS), the authors point out nine important experimental results. On the basis of these results, the authors have argued that the two-dimension, two-subsystem Hamiltonian is the appropriate starting point for describing the normal state of HTS. By this Hamiltonian, using the decoupling approximation of Green's function method by Kaga through numerical calculations, the authors have obtained the temperature dependent pseudogap in the density of states (DOS), which is consistent qualitatively with the experimental results by angle-resolved photoemission spectroscopy (ARPES). Theoretically, this Hamiltonian has the superconducting order parameter of d + s symmetry with d-wave as the main component, which is consistent with experiments. Further, the quantum electronic liquid in HTS is a near Fermi liquid in which there is coexistence of the delocalized states and nearly localized states, and there is finite probability for the nearly localized carriers to form the nearly localized carrier pairs at any finite temperature.

关键词： high temperature superconductivity pseudogap symmetry near Fermi liquid.

Liquid nitrogen level meter for high-temperature superconductor (HTS)

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Journal of Central South University 2012年第11期19卷 3100-3104页

作者： PARK Heecheol JEONG Hwanjun LEE Changyeung KIM Purn CHO Jangwon KIM Seokho School of Mechatronics Changwon National UniversityChangwon 641-773Korea

Many kinds of high temperature superconductor （HTS） power machines such as HTS cable, HTS fault current limitcr and HTS magnet are cooled by liquid nitrogen. The level of liquid nitrogen should be monitored and controlled to ensure the thermal stability and the dielectric strength as well. To measure the level, capacitance method and differential pressure method are usually used. However, each method has installation difficulties and measurement errors for unsteady state operation with varying system pressure. A new liquid level meter using a 2G HTS conductor is described, which has similar structure with the liquid helium level meter with NbTi filament. The level meter is fabricated with a parallel connected heater, which helps the separation of the superconducting region and normal region, considering the critical temperature, large heat capacity of conductor and cooling characteristics. The level of liquid nitrogen can be obtained from the measured voltage signal along the 2G HTS conductor. Design, fabrication and test results of the new liquid nitrogen level meter are presented.

关键词： high temperature superconductivity liquid nitrogen level meter quench