A coexistence that CuO<sub>2</sub> planes can see

doi:10.1126/science.aba9482

GSTDTAP > 气候变化

DOI	10.1126/science.aba9482
	A coexistence that CuO₂ planes can see
	Inna Vishik
	2020-08-14
发表期刊	Science
出版年	2020
英文摘要	Superconductivity is a zero-resistance quantum-coherent state with applications to sensing, powerful electromagnets, and computing. Some materials have mysterious reasons for becoming superconducting, which continues to drive interest in the topic. Cuprates exhibit the highest superconducting transition temperature ( T c) of known materials under ambient pressure, exceeding the boiling point of liquid nitrogen in many compounds. On page 833 of this issue, Kunisada et al. ([ 1 ][1]) show how a seldom-studied quintuple-layer cuprate, Ba2Ca4Cu5O10(F,O)2, can help uncover the elusive superconductivity mechanism in these high-temperature superconductors. Superconductivity is not found by itself in cuprates. Instead, interrelationships between multiple competing, coexisting, and intertwined electronic phases may be key to formulating a mechanism for cuprate superconductivity ([ 2 ][2], [ 3 ][3]). Despite this complexity, most experimental studies on cuprates have focused on a small handful of compounds ([ 4 ][4], [ 5 ][5]), even though hundreds of different cuprate superconductors have been identified. Key insights can be overlooked by studying compounds that manifest a particular phenomenon only weakly. In this context, seldom-studied cuprate compounds give a fresh perspective on a long-standing problem, especially if they are compatible with both surface spectroscopies and bulk transport measurements. Cuprate properties can be tuned by modifying the number of charge carriers with a process called doping. Hole-doped cuprates involve introducing positive charge and achieve the highest T c. The parent compound with no doping is an electrical insulator, owing to strong electron-electron repulsion, and the spins on adjacent copper sites point in opposite directions, making it an antiferromagnet. The antiferromagnetism is diminished by hole-doping, allowing superconductivity to emerge. The relationship between the antiferromagnetic electronic phase and the mechanism of superconductivity has driven cuprate research. Moreover, other families of unconventional superconductors—including heavy fermion materials, organic superconductors, and iron-based superconductors—have similar phenomenology in which superconductivity appears proximate to the demise of antiferromagnetic order. This has led to proposals of a common mechanism of superconductivity between these different superconductors, invoking dynamic excitations related to antiferromagnetism in joining electrons into Cooper pairs ([ 6 ][6]). Despite this, the electronic and superconducting properties inherent to lightly hole-doped cuprates are still poorly understood. Ba2Ca4Cu5O10(F,O)2 offers a distinct perspective by permitting access to the doping regime where superconductivity is in closest proximity to long-range antiferromagnetism while minimizing disorder. All cuprates share a structural unit of copper oxide (CuO2) planes, which participate most heavily in superconductivity. Doped electrons or holes are transferred to the CuO2 planes, but the elemental substitution actually happens in the portion of the crystal structure between blocks of CuO2 planes called the charge-reservoir layers (CRLs). The composition of the CRLs distinguishes different cuprate compounds. Cuprates can have one or more CuO2 planes in a structural block close to one another, separated by intervening CRLs. The highest T c is typically found in compounds with three or more adjacent CuO2 planes ([ 7 ][7]), making such materials highly promising for understanding factors that enhance T c. In such compounds, one or more inner CuO2 planes (IPs) are not directly adjacent to the CRL. Because of this distance, IPs tend to have smaller doping and less disorder. Ba2Ca4Cu5O10(F,O)2 is a quintuple-layer cuprate, meaning that there are two types of IPs: one in the middle of the stack and two equivalently in the second and fourth positions. In Ba2Ca4Cu5O10(F,O)2, each of the structurally inequivalent CuO2 planes tells a distinct story (see the figure). The outer planes yield information consistent with commonly studied single- and double-layer cuprates, whereas the two types of IPs reveal two CuO2 planes that are lightly hole-doped and still superconducting and one IP which is very lightly hole-doped and not superconducting. ![Figure][8] Superconducting five-layer cuprate The Ba2Ca4Cu5O10(F,O)2 superconductor has two outer CuO2 planes (OP), and two inner CuO2 planes (IP1) that sandwich a fifth CuO2 layer (IP). Each layer has properties that combine to allow the compound to have both antiferromagnetism and superconductivity. GRAPHIC: C. BICKEL/ SCIENCE Kunisada et al. first confirmed long-range antiferromagnetism in the IPs using two techniques: quantum oscillations and angle-resolved photoemission spectroscopy (ARPES). This multitechnique approach indicated a common ground state in high magnetic field and zero magnetic field. Evidence for antiferromagnetism was observed using the size and location of the Fermi surface, which is the locus of zero-energy electronic excitations. This surface is also important for circumscribing the origin of superconductivity. The superconducting gap is an excitation tied to the Fermi surface and reflects the energy required to break a Cooper pair, the bound pair of electrons that forms the charge carrier unit in a superconductor. In Ba2Ca4Cu5O10(F,O)2, Kunisada et al. observed a superconducting gap on the outer IPs. The magnitude of the superconducting gap is large enough to suggest that superconductivity on these IPs is not a consequence of simply being near to the superconducting outer planes but instead that the IPs themselves are favorable for superconductivity while simultaneously hosting antiferromagnetism. Moreover, the IP superconducting gap does not extend to the antinodal regions of the Brillouin zone, where the superconducting gap is at a maximum in other cuprates, disputing proposals that superconductivity originates there. These results indicate that cuprate superconductivity can robustly coexist with long-range antiferromagnetism. Further, this study helps disentangle doping from chemical disorder to highlight how the latter may play a greater role in more commonly studied cuprates. Understanding how superconductivity develops from an antiferromagnetic insulator may be key to uncovering the elusive mechanism of superconductivity in cuprate high-temperature superconductors. The high-quality surface-sensitive ARPES and bulk-sensitive quantum oscillation observations on Ba2Ca4Cu5O10(F,O)2 move the field closer to this goal while highlighting the importance of continued investigation of cuprates with three or more adjacent CuO2 layers. 1. [↵][9]1. S. Kunisada et al ., Science 369, 833 (2020). [OpenUrl][10][Abstract/FREE Full Text][11] 2. [↵][12]1. M. Hashimoto, 2. I. M. Vishik, 3. R.-H. He, 4. T. P. Devereaux, 5. Z.-X. Shen , Nat. Phys. 10, 483 (2014). [OpenUrl][13][CrossRef][14] 3. [↵][15]1. E. Fradkin, 2. S. A. Kivelson, 3. J. M. Tranquada , Rev. Mod. Phys. 87, 457 (2015). [OpenUrl][16][CrossRef][17] 4. [↵][18]1. S. Hüfner, 2. M. A. Hossain, 3. A. Damascelli, 4. G. A. Sawatzky , Rep. Prog. Phys. 71, 062501 (2008). [OpenUrl][19][CrossRef][20] 5. [↵][21]1. C. C. Homes et al ., Nature 430, 539 (2004). [OpenUrl][22][CrossRef][23][PubMed][24] 6. [↵][25]1. D. J. Scalapino , Rev. Mod. Phys. 84, 1383 (2012). [OpenUrl][26][CrossRef][27] 7. [↵][28]1. A. 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领域	气候变化 ; 资源环境
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文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/288067
专题	气候变化资源环境科学
推荐引用方式 GB/T 7714	Inna Vishik. A coexistence that CuO₂ planes can see[J]. Science,2020.
APA	Inna Vishik.(2020).A coexistence that CuO₂ planes can see.Science.
MLA	Inna Vishik."A coexistence that CuO₂ planes can see".Science (2020).