共查询到18条相似文献,搜索用时 156 毫秒
1.
2.
3.
4.
超导是一种奇异的宏观量子现象.100多年来,已发现的超导体主要分为两类:以金属或者合金为代表的常规超导体以及以铜氧化物和铁基高温超导体为代表的非常规超导体.常规超导体的超导机理能被BCS超导理论完美解释,但高温超导体的超导机理至今仍未达成共识,已经成为凝聚态物理领域中长期争论且充满挑战的重大科学问题.从实验上揭示非常规超导材料的微观电子结构,是理解其奇异正常态和超导电性机理、建立新理论的前提和基础.角分辨光电子能谱技术,由于可以实现对材料中电子的能量、动量和自旋的直接测量,在高温超导研究中发挥了重要的作用.本文综述了我们利用角分辨光电子能谱技术在铜氧化物和铁基高温超导体电子结构和超导机理研究中取得的一些进展,主要包括母体的电子结构、正常态的非费米液体行为、超导态的能带和超导能隙结构以及多体相互作用等.这些结果为理解铜氧化物和铁基高温超导体的物性及超导机理提供了重要的信息. 相似文献
5.
6.
铜氧化物超导体和铁基超导体是人类相继发现的两类高温超导家族,它们的高温超导机理是凝聚态物理领域中长期争论但悬而未决的重大问题.对铁基超导体广泛而深入的研究,以及与铜氧化物高温超导体的对比,对于发展新的量子固体理论、解决高温超导机理、探索新的超导体以及超导实际应用都具有重要意义.固体材料的宏观物性由其微观电子结构所决定,揭示高温超导材料的微观电子结构是理解高温超导电性的前提和基础.由于角分辨光电子能谱技术具有独特的同时对能量、动量甚至自旋的分辨能力,已成为探测材料微观电子结构的最直接、最有力的实验手段,在高温超导体的研究中发挥了重要作用.本文综述了在不同体系铁基超导体中费米面拓扑结构、超导能隙大小和对称性、轨道三维性和选择性、电子耦合模式等的揭示和发现,为甄别和提出铁基超导新理论、解决高温超导机理问题提供重要依据. 相似文献
7.
鹊桥仙·二月听风梅声唱晚,金陵散懒。新雨随风迷漫。早春颐指紫金山,十里峻、浮香浅浅。碧池弄暖,珠林晓涧。又是烟霞舒卷。路边桃李上寒枝,道不尽,韶华看惯。Ⅺ.铁基超导体的奇特磁结构高温超导(包括铁基超导)电子配对机制是超导物理的核心,这让多少人魂牵梦绕几十年。除了最近有很强的声音声称铜基和铁基高温超导依然是BCS机制占主导外,自旋涨落导致铁基超导配对也是一种声音,虽然超导电性跟磁性从来就不是一路人。所以,铁基超导中磁性和磁结构研究一直是被寄予厚望的主流,甚至超越对超导态本身的关注。毕竟,将超导态与磁性联系起来,是超越BCS之外的新物理。 相似文献
8.
最近,由于在铁基Ln(O,F)FeAs化合物及其相关化合物中发现具有高于40K的超导电性,层状的铁基化合物引起了凝聚态物理学界很大的兴趣和关注.在随后的研究中发现,在该类材料中最高超导临界温度可达到55K.这些重要的发现使得人们又重新对高温超导体的探索产生了极大的兴趣,并且为研究高温超导的机理提供了新的一类材料.文章主要介绍了作者所在组在新型铁基超导体方面的最新研究进展,包括:(1)铁基超导材料探索研究;(2)铁基超导体的单晶制备及物性研究;(3)铁基超导体的电子相图及自旋密度波(SDW)和超导共存研究;(4)同位素交换对超导转变和SDW转变的效应.最后,在已完成的工作基础上提出了一些今后的研究方向和发展前景. 相似文献
9.
10.
人们认为,超导体在电力方面出现大规模应用的时间距离我们还非常遥远.然而,随着最近几年来实用高温超导材料的研制取得重大的进展,高温超导电力技术的应用已经成为现实,预期将在2010年左右出现大规模的应用,并将带来电力工业的革命.因此,下一个10年将是国际超导技术竞争最关键的10年.我国的经济发展很快,电能需求量增加十分迅速,对电能质量的要求也越来越高.常规电力技术已经无法满足我国电力发展的需要,超导电力技术是实现我国电力发展目标的必由之路.文章有代表性地介绍了超导电缆、超导限流器、超导磁储能系统、超导变压器和超导旋转电机等的基本工作原理及研究发展历史,并着重介绍高温超导电力应用研究的现状、应用前景、经济可行性及基本物理问题. 相似文献
11.
在铁基超导体中存在着多种有序态,例如电子向列相和自旋密度波等,从而呈现出丰富的物理现象.输运性质的测量能为认识铁基超导体的低能激发提供极为有用的信息.铁砷超导体由于其电子结构的多能带特性,其电阻率和霍尔系数与温度的关系出现多样性的变化,但在正常态并没有看到有类似铜氧化物超导体的赝能隙打开等奇异行为.在空穴型掺杂的铁基超导体中观测到霍尔系数在低温下变号,对应温区的电阻率上出现一个很宽的鼓包等,可能是从非相干到相干态的转变.热电势行为也表现出与铜氧化物超导体的明显差异,比如铁基超导体的正常态热电势的绝对值反而在最佳掺杂区是最大的,这也许跟强的带间散射有关.能斯特效应表明铁基超导体在Tc以上的超导位相涨落并不明显,与铜氧化物超导体存在明显差别.在铁基超导体上所显示出来的这些反常热电性质,并没有在类似结构的镍基超导体(如LaNiAsO)上观测到,镍基超导体表现得更像一个通常的金属.这些均说明铁基超导体的奇异输运性质与其高温超导电性存在内在的关联,这些因素是建立其超导机理时需要考虑进去的. 相似文献
12.
We show that the layered-structure BaCuS2 is a moderately correlated electron system in which the electronic structure of the CuS layer bears a resemblance to those in both cuprates and iron-based superconductors.Theoretical calculations reveal that the in-plane d-p σ*-bonding bands are isolated near the Fermi level.As the energy separation between the d and p orbitals are much smaller than those in cuprates and iron-based superconductors,BaCuS2 is expected to be moderately correlated.We suggest that this material is an ideal system to study the competitive/collaborative nature between two distinct superconducting pairing mechanisms,namely the conventional BCS electron-phonon interaction and the electron-electron correlation,which may be helpful to establish the elusive mechanism of unconventional high-temperature superconductivity. 相似文献
13.
铁基超导体作为除铜氧化物超导体之外的第二类高温超导体,自从被发现以来其超导电性的成因就备受关注。早期有人针对同时具有空穴型费米口袋和电子型费米口袋的铁砷基超导体提出了S±配对模式,而且得到中子散射和隧道谱实验的初步支持。这一配对模型的基础是需要在布里渊区同时具有空穴型和电子型费米面。但是铁基超导体的费米面因材料而异,新发现的很多铁硒基超导体因缺乏空穴型费米面,对S±电子配对模型来说是一个挑战。文章综述了过去几年来作者在这方面取得的工作进展。运用高精度的扫描隧道显微镜,在不同铁基超导体系中,针对超导能隙结构,或超导序参量的性质进行了仔细研究。首先作者在铁砷基超导体NaFe1-xCoxAs和Ba1-xKxFe 2As2中利用无磁性杂质态测量和隧道谱测量,发现S±的明确证据。进一步,在只有电子型费米面的(Li1−xFex)OHFeSe超导材料中发现两个各向异性的超导能隙,利用准粒子相干散射实验第一次把这两个超导能隙对应到由电子型费米面套叠或杂化后形成的内外两套费米面上。通过非磁性杂质诱导产生的能隙内杂质态和新型电子驻波相位敏感实验的探测,证明该材料中超导能隙符号也发生反转。因此作者的系列工作统一了有和没有空穴型费米面的铁基超导体的能隙形式,支持排斥势是导致电子配对和超导电性产生的关键因素。 相似文献
14.
Spin fluctuations and unconventional superconducting pairing in iron-based superconductors
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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 char- acteristics 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. 相似文献
15.
Pairing occurs in conventional superconductors through a reduction of the electronic potential energy accompanied by an increase in kinetic energy. In the underdoped cuprates, optical experiments show that pairing is driven by a reduction of the electronic kinetic energy. Using the dynamical cluster approximation we study superconductivity in the two-dimensional Hubbard model. We find that pairing is indeed driven by the kinetic energy and that superconductivity evolves from an unconventional state with partial spin-charge separation, to a superconducting state with quasiparticle excitations. 相似文献
16.
Electronic phase diagram of NaFe_(1-x)Co_xAs investigated by scanning tunneling microscopy
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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-T c 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. 相似文献
17.
18.
G. R. Stewart 《物理学进展》2017,66(2):75-196
‘Conventional’ superconductivity, as used in this review, refers to electron–phonon-coupled superconducting electron pairs described by BCS theory. Unconventional superconductivity refers to superconductors where the Cooper pairs are not bound together by phonon exchange but instead by exchange of some other kind, e.g. spin fluctuations in a superconductor with magnetic order either coexistent or nearby in the phase diagram. Such unconventional superconductivity has been known experimentally since heavy fermion CeCu2Si2, with its strongly correlated 4f electrons, was discovered to superconduct below 0.6?K in 1979. Since the discovery of unconventional superconductivity in the layered cuprates in 1986, the study of these materials saw Tc jump to 164?K by 1994. Further progress in high-temperature superconductivity would be aided by understanding the cause of such unconventional pairing. This review compares the fundamental properties of 9 unconventional superconducting classes of materials – from 4f-electron heavy fermions to organic superconductors to classes where only three known members exist to the cuprates with over 200 examples – with the hope that common features will emerge to help theory explain (and predict!) these phenomena. In addition, three new emerging classes of superconductors (topological, interfacial – e.g. FeSe on SrTiO3, and H2S under high pressure) are briefly covered, even though their ‘conventionality’ is not yet fully determined. 相似文献