Content of TOPICAL REVIEW—Iron-based high temperature superconductors in our journal

Published in last 1 year |  In last 2 years |  In last 3 years |  All Please wait a minute... For selected: Download citations EndNote Ris BibTeX Toggle thumbnails Select Molecular beam epitaxy and superconductivity of stoichiometric FeSe and KxFe2-ySe2 crystalline films Wang Li-Li (王立莉), Ma Xu-Cun (马旭村), Chen Xi (陈曦), Xue Qi-Kun (薛其坤) Chin. Phys. B, 2013, 22 (8): 086801.   DOI: 10.1088/1674-1056/22/8/086801 Abstract （742）      PDF （2447KB）（1011）       Knowledge map    Our recent progress in the fabrication of FeSe and KxFe2-ySe2 ultra thin films and the understanding of their superconductivity properties is reviewed. The growth of high-quality FeSe and KxFe2-ySe2 films is achieved in a well controlled manner by molecular beam epitaxy. The high-quality stoichiometric and superconducting crystalline thin films allow us to investigate the intrinsic superconductivity properties and the interplay between the superconductivity and the film thickness, the local structure, the substrate, and magnetism. In situ low-temperature scanning tunneling spectra reveal the nodes and the twofold symmetry in FeSe, high-temperature superconductivity at the FeSe/SrTiO3 interface, phase separation and magnetic order in KxFe2-ySe2, and the suppression of superconductivity by twin boundaries and Fe vacancies. Our findings not only provide fundamental information for understanding the mechanism of unconventional superconductivity, but also demonstrate a powerful way of engineering superconductors and raising the transition temperature. Select Electron-phonon coupling in cuprate and iron-based superconductors revealed by Raman scattering Zhang An-Min (张安民), Zhang Qing-Ming (张清明) Chin. Phys. B, 2013, 22 (8): 087103.   DOI: 10.1088/1674-1056/22/8/087103 Abstract （740）      PDF （2103KB）（1342）       Knowledge map    Electron-phonon coupling (EPC) in cuprate and iron-based superconducting systems, as revealed by Raman scattering, is briefly reviewed. We introduce how to extract the coupling information through phonon lineshape. Then we discuss the strength of EPC in different high-temperature superconductor (HTSC) systems and possible factors affecting the strength. A comparative study between Raman phonon theories and experiments allows us to gain insight into some crucial electronic properties, especially superconductivity. Finally, we summarize and compare EPC in the two existing HTSC systems, and discuss what role it may play in the HTSC. Select Exploration of iron-chalcogenide superconductors Dong Chi-Heng (董持衡), Wang Hang-Dong (王杭栋), Fang Ming-Hu (方明虎) Chin. Phys. B, 2013, 22 (8): 087401.   DOI: 10.1088/1674-1056/22/8/087401 Abstract （518）      PDF （2614KB）（848）       Knowledge map    Iron-chalcogenide compounds with FeSe(Te, S) layers did not attract much attention until the discovery of high-Tc superconductivity (SC) in the iron-pnictide compounds at the begining of 2008. Compared with FeAs-based superconductors, iron-chalcogenide superconductors have aroused enormous enthusiasm to study the relationship between SC and magnetisms with several distinct features, such as different antiferromagnetic ground states with relatively large moments in the parents, indicating possibly different superconducting mechanisms, the existence of the excess Fe atoms or Fe vacancies in the crystal lattice. Another reason is that the large single crystals are easily grown for the iron-chalcogenide compounds. This review will focus on our exploration for the iron-chalcogenide superconductors and discussion on several issues, including the crystal structure, magnetic properties, superconductivity, and phase separation. Some of them reach a consensus but some important questions still remain to be answered. Select Spin, charge, and orbital orderings in iron-based superconductors Jiang Qing (江庆), Kang Yao-Tai (康耀太), Yao Dao-Xin (姚道新) Chin. Phys. B, 2013, 22 (8): 087402.   DOI: 10.1088/1674-1056/22/8/087402 Abstract （804）      PDF （494KB）（724）       Knowledge map    In this article, we briefly review spin, charge, and orbital orderings in iron-based superconductors, as well as the multi-orbital models. The interplay of spin, charge, and orbital orderings is a key to understand the high temperature superconductivity. As an illustration, we use the two-orbital model to show the spin and charge orderings in iron-based superconductors based on the mean-field approximation in real space. The typical spin and charge orderings are shown by choosing appropriate parameters, which are in good agreement with experiments. We also show the effect of Fe vacancies, which can introduce the nematic phase and interesting magnetic ground states. The orbital ordering is also discussed in iron-based superconductors. It is found that disorder may play a role to produce the superconductivity. Select Optical spectroscopy studies on FeTe1-xSex and AxFe2-ySe2 (A=K, Rb, Cs)：A brief overview Yuan Rui-Hua (原瑞花), Wang Nan-Lin (王楠林) Chin. Phys. B, 2013, 22 (8): 087404.   DOI: 10.1088/1674-1056/22/8/087404 Abstract （731）      PDF （2714KB）（895）       Knowledge map    In this short overview, we summarize the optical spectroscopy studies on iron selenide superconducting systems FeTe1-xSex and AxFe2-ySe2. We elaborate that optical spectroscopy measurements yield fruitful information about the band structure evolution across the AFM phase transition temperature, the electronic correlation effect, the superconducting pairing energy gap, the condensed carrier density or penetration depth, the inhomogeneity and the nanoscale phase separation between superconductivity and antiferromagnetism in those systems. Select Physics picture from neutron scattering study on Fe-based superconductors Bao Wei (鲍威) Chin. Phys. B, 2013, 22 (8): 087405.   DOI: 10.1088/1674-1056/22/8/087405 Abstract （597）      PDF （259KB）（687）       Knowledge map    Neutron scattering, with its ability to measure the crystal structure, the magnetic order, and the structural and magnetic excitations, plays an active role in investigating various families of Fe-based high-Tc superconductors. Three different types of antiferromagnetic orders have been discovered in the Fe plane, but two of them cannot be explained by the spin-densitywave (SDW) mechanism of nesting Fermi surfaces. Noticing the close relation between antiferromagnetic order and lattice distortion in orbital ordering from previous studies on manganites and other oxides, we have advocated orbital ordering as the underlying common mechanism for the structural and antiferromagnetic transitions in the 1111, 122, and 11 parent compounds. We observe the coexistence of antiferromagnetic order and superconductivity in the (Ba,K)Fe2As2 system, when its phase separation is generally accepted. Optimal Tc is proposed to be controlled by the local FeAs4 tetrahedron from our investigation on the 1111 materials. The Bloch phase coherence of the Fermi liquid is found crucial to the occurrence of bulk superconductivity in iron chalcogenides of both the 11 and the 245 families. Iron chalcogenides carry a larger staggered magnetic moment (> 2 μB/Fe) than that in iron pnictides (< 1μB/Fe) in the antiferromagnetic order. Normal state magnetic excitations in the 11 superconductor are of the itinerant nature while in the 245 superconductor the spin-waves of localized moments. The observation of superconducting resonance peak provides a crucial piece of information in current deliberation of the pairing symmetry in Fe-based superconductors. Select Photoemission study of iron-based superconductor Liu Zhong-Hao (刘中灝), Cai Yi-Peng (蔡贻鹏), Zhao Yan-Ge (赵彦阁), Jia Lei-Lei (贾雷雷), Wang Shan-Cai (王善才) Chin. Phys. B, 2013, 22 (8): 087406.   DOI: 10.1088/1674-1056/22/8/087406 Abstract （519）      PDF （2381KB）（730）       Knowledge map    The iron-based superconductivity (IBSC) is a great challenge in correlated system. Angle-resolved photoemission spectroscopy (ARPES) provides electronic structure of the IBSCs, the pairing strength, and the order parameter symmetry. Here, we briefly review the recent progress in IBSCs and focus on the results from ARPES. The ARPES study shows the electronic structure of "122", "111", "11", and "122*" families of IBSCs. It has been agreed that the IBSCs are unconventional superconductors in strong coupling region. The order parameter symmetry basically follows s± form with considerable out-of-plane contribution. Select Angle-resolved photoemission spectroscopy study on iron-based superconductors Ye Zi-Rong (叶子荣), Zhang Yan (张焱), Xie Bin-Ping (谢斌平), Feng Dong-Lai (封东来) Chin. Phys. B, 2013, 22 (8): 087407.   DOI: 10.1088/1674-1056/22/8/087407 Abstract （790）      PDF （1412KB）（1796）       Knowledge map    Angle-resolved photoemission spectroscopy (ARPES) has played an important role in determining the band structure and the superconducting gap structure of iron-based superconductors. In this paper, from the ARPES perspective, we briefly review the main results from our group in recent years on the iron-based superconductors and their parent compounds, and depict our current understanding on the antiferromagnetism and superconductivity in these materials. Select Microstructure and structural phase transitions in iron-based superconductors Wang Zhen (王臻), Cai Yao (蔡瑶), Yang Huai-Xin (杨槐馨), Tian Huan-Fang (田焕芳), Wang Zhi-Wei (王秩伟), Ma Chao (马超), Chen Zhen (陈震), Li Jian-Qi (李建奇) Chin. Phys. B, 2013, 22 (8): 087409.   DOI: 10.1088/1674-1056/22/8/087409 Abstract （579）      PDF （3375KB）（1200）       Knowledge map    Crystal structures and microstructural features, such as structural phase transitions, defect structures, and chemical and structural inhomogeneities, are known to have profound effects on the physical properties of superconducting materials. Recently, many studies on the structural properties of Fe-based high-Tc superconductors have been published. This review article will mainly focus on the typical microstructural features in samples that have been well characterized by physical measurements. (i) Certain common structural features are discussed, in particular, the crystal structural features for different superconducting families, the local structural distortions in the Fe2Pn2 (Pn=P, As, Sb) or Fe2Ch2 (Ch=S, Se, Te) blocks, and the structural transformations in the 122 system. (ii) In FeTe(Se) (11 family), the superconductivity, chemical and structural inhomogeneities are investigated and discussed in correlation with superconductivity. (iii) In the K0.8Fe1,6+xSe2 system, we focus on the typical compounds with emphasis on the Fe-vacancy order and phase separations. The microstructural features in other superconducting materials are also briefly discussed. Select Crystal chemistry and structural design of iron-based superconductors Jiang Hao (蒋好), Sun Yun-Lei (孙云蕾), Xu Zhu-An (许祝安), Cao Guang-Han (曹光旱) Chin. Phys. B, 2013, 22 (8): 087410.   DOI: 10.1088/1674-1056/22/8/087410 Abstract （610）      PDF （2244KB）（1572）       Knowledge map    The second class of high-temperature superconductors (HTSCs), iron-based pnictides and chalcogenides, necessarily contain Fe2X2 ("X" refers to a pnictogen or a chalcogen element) layers, just like the first class of HTSCs which possess the essential CuO2 sheets. So far, dozens of iron-based HTSCs, classified into nine groups, have been discovered. In this article, the crystal-chemistry aspects of the known iron-based superconductors are reviewed and summarized by employing "hard and soft acids and bases (HSAB)" concept. Based on these understandings, we propose an alternative route to exploring new iron-based superconductors via rational structural design. Select Spin fluctuations and unconventional superconducting pairing in iron-based superconductors Yu Shun-Li (于顺利), Li Jian-Xin (李建新) Chin. Phys. B, 2013, 22 (8): 087411.   DOI: 10.1088/1674-1056/22/8/087411 Abstract （750）      PDF （3656KB）（1197）       Knowledge map    In this article, we review the recent theoretical works on the spin fluctuations and superconductivity in iron-based superconductors. Using the fluctuation exchange approximation and multi-orbital tight-binding models, we study the characteristics of the spin fluctuations and the symmetries of the superconducting gaps for different iron-based superconductors. We explore the systems with both electron-like and hole-like Fermi surfaces (FS) and the systems with only the electron-like FS. We argue that the spin-fluctuation theories are successful in explaining at least the essential part of the problems, indicating that the spin fluctuation is the common origin of superconductivity in iron-based superconductors. Select Exploring FeSe-based superconductors by liquid ammonia method Ying Tian-Ping (应天平), Wang Gang (王刚), Jin Shi-Feng (金士锋), Shen Shi-Jie (申士杰), Zhang Han (张韩), Zhou Ting-Ting (周婷婷), Lai Xiao-Fang (赖晓芳), Wang Wan-Yan (王皖燕), Chen Xiao-Long (陈小龙) Chin. Phys. B, 2013, 22 (8): 087412.   DOI: 10.1088/1674-1056/22/8/087412 Abstract （766）      PDF （2145KB）（849）       Knowledge map    Our recent progress on the preparation of a series of new FeSe-based superconductors and the clarification of SC phases in potassium-intercalated iron selenides are reviewed here. By the liquid ammonia method, metals Li, Na, Ca, Sr, Ba, Eu, and Yb are intercalated in between FeSe layers and form superconductors with transition temperatures of 30 K～46 K, which cannot be obtained by high-temperature routes. In the potassium-intercalated iron selenides, we demonstrate that at least two SC phases exist, KxFe2Se2(NH3)y (x ≈ 0.3 and 0.6), determined mainly by the concentration of potassium. NH3 has little, if any, effect on superconductivity, but plays an important role in stabilizing the structures. All these results provide a new starting point for studying the intrinsic properties of this family of superconductors, especially for their particular electronic structures. Select Electronic phase diagram of NaFe1-xCoxAs investigated by scanning tunneling microscopy Zhou Xiao-Dong (周晓东), Cai Peng (蔡鹏), Wang Ya-Yu (王亚愚) Chin. Phys. B, 2013, 22 (8): 087413.   DOI: 10.1088/1674-1056/22/8/087413 Abstract （538）      PDF （6375KB）（1079）       Knowledge map    Our recent scanning tunneling microscopy (STM) studies of the NaFe1-xCoxAs phase diagram over a wide range of dopings and temperatures are reviewed. Similar to the high-Tc cuprates, the iron-based superconductors lie in close proximity to a magnetically ordered phase. Therefore, it is widely believed that magnetic interactions or fluctuations play an important role in triggering their Cooper pairings. Among the key issues regarding the electronic phase diagram are the properties of the parent spin density wave (SDW) phase and the superconducting (SC) phase, as well as the interplay between them. The NaFe1-xCoxAs is an ideal system for resolving these issues due to its rich electronic phases and the charge-neutral cleaved surface. In our recent work, we directly observed the SDW gap in the parent state, and it exhibits unconventional features that are incompatible with the simple Fermi surface nesting picture. The optimally doped sample has a single SC gap, but in the underdoped regime we directly viewed the microscopic coexistence of the SDW and SC orders, which compete with each other. In the overdoped regime we observed a novel pseudogap-like feature that coexists with superconductivity in the ground state, persists well into the normal state, and shows great spatial variations.The rich electronic structures across the phase diagram of NaFe1-xCoxAs revealed here shed important new light for defining microscopic models of the iron-based superconductors. In particular, we argue that both the itinerant electrons and local moments should be considered on an equal footing in a realistic model. Select Review of nuclear magnetic resonance studies on iron-based superconductors Ma Long (马龙), Yu Wei-Qiang (于伟强) Chin. Phys. B, 2013, 22 (8): 087414.   DOI: 10.1088/1674-1056/22/8/087414 Abstract （757）      PDF （3622KB）（1710）       Knowledge map    The newly discovered iron-based superconductors have triggered renewed enormous research interest in the condensed matter physics community. Nuclear magnetic resonance (NMR) is a low-energy local probe for studying strongly correlated electrons, and particularly important for high-TC superconductors. In this paper, we review NMR studies on the structural transition, antiferromagnetic order, spin fluctuations, and superconducting properties of several iron-based high-TC superconductors, including LaFeAsO1-xFx, LaFeAsO1-x, BaFe2As2, Ba1-xKxFe2As2, Ca0.23Na0.67Fe2As2, BaFe2(As1-xPx)2, Ba(Fe1-xRux)2As2, Ba(Fe1-xCox)2As2, Li1+xFeAs, LiFe1-xCoxAs, NaFeAs, NaFe1-xCoxAs, KyFe2-xSe2, and (Tl,Rb)yFe2-xSe2. Select Interplay of superconductivity and d-f correlation in CeFeAs1-xPxO1-yFy Luo Yong-Kang (罗永康), Li Yu-Ke (李玉科), Wang Cao (王操), Lin Xiao (林效), Dai Jian-Hui (戴建辉), Cao Guang-Han (曹光旱), Xu Zhu-An (许祝安) Chin. Phys. B, 2013, 22 (8): 087415.   DOI: 10.1088/1674-1056/22/8/087415 Abstract （601）      PDF （3719KB）（782）       Knowledge map    The recent discovery of high-temperature superconductivity in iron-based pnictides (chalcogenides) not only triggers tremendous enthusiasm in searching for new superconducting materials, but also opens a new avenue to the study of the Kondo physics. CeFeAsO is a parent compound of the 1111-type iron-based superconductors. It shows 3d-antiferromagnetic (AFM) ordering below ～139 K and 4f-AFM ordering below ～4 K. On the other hand, the phosphide CeFePO is a ferromagnetically correlated heavy-fermion (HF) metal with Kondo scale TK～10 K. These properties set up a new platform for research of the interplay among magnetism, Kondo effect, and superconductivity (SC). In this review, we present the recent progress in the study of chemical pressure effect in CeFeAsO1-yFy (y=0 and 0.05). This P/As-doping in CeFeAsO serves as an effective controlling parameter which leads to two magnetic critical points, xc1≈0.4 and xc2≈0.92, associated with suppression of 3d and 4f magnetism, respectively. We also observe a turning point of AFM-FM ordering of Ce3+ moment at xc3≈0.37. The SC is absent in the phase diagram, which is attributed to the destruction to Cooper pair by Ce-FM fluctuations in the vicinity of xc1. We continue to investigate CeFeAs1-xPxO0.95F0.05. With the separation of xc1 and xc3, this chemical pressure results in a broad SC region 0≤x≤q 0.53, while the original HF behavior is driven away by 5% F- doping. Different roles of P and F dopings are addressed, and the interplay between SC and Ce-4f magnetism is also discussed.