A touch more unconventional

doi:10.1126/science.abi6855

GSTDTAP > 气候变化

DOI	10.1126/science.abi6855
	A touch more unconventional
	Eva Benckiser
	2021-07-09
发表期刊	Science
出版年	2021
英文摘要	Superconductivity is one of the most fascinating, macroscopically observable quantum phenomena. A notable aspect of its description is the existence of an attractive interaction, a “glue,” between electrons. This can bind them into Cooper pairs, which then condense into a common superconducting ground state. In contrast to conventional superconductors, which are described by the theory of Bardeen, Cooper, and Schrieffer, a primary phonon-mediated pairing mechanism is unlikely in the high-temperature ( T c) superconducting cuprates, and therefore they are referred to as unconventional. One characteristic of all high- T c cuprates are the strong, quasi–two-dimensional antiferromagnetic correlations, with spin waves or magnons as possible alternative pairing glue. On page 213 of this issue, Lu et al. ([ 1 ][1]) report on antiferromagnetic magnon-like spin excitations in superconducting infinite-layer nickelate thin films. The recent discovery of this new class of potentially unconventional superconductors, Nd1− x Sr x NiO2 ([ 2 ][2]), has sparked great interest. Although the T c of 15 K is lower than the T c ≤ 130 K in the cuprates, their structural and electronic similarity immediately raised the possibility of magnetic correlations and a related pairing mechanism. To this point, the authors measured the spin wave dispersion of Nd1− x Sr x NiO2 with resonant inelastic x-ray scattering. A nearest-neighbor superexchange coupling of J = 64 meV was determined, which quantifies the coupling of two neighboring magnetic nickel ions through the nonmagnetic oxygen ion in between. This large superexchange interaction is unexpected because it is not much smaller than the J found in cuprates of over 100 meV. The outstanding question is whether the new nickelate superconductors are just like the high- T c cuprates. At first glance, the isostructural transition-metal-oxide planes contain monovalent Ni1+ ions that are isoelectronic to Cu2+, with a single spin ½ in the planar 3 d x 2− y 2 orbital on a square lattice (see the figure). In both materials, strong electron-electron correlations cause the partially occupied transition-metal d -band to split up into so-called lower and upper Hubbard subbands. One major difference in the electronic structure is the relative energy of the oxygen-2 p –derived bands with respect to the Hubbard subbands. Whereas in cuprates, the 2 p bands lie in between, in nickelates, they are located below both subbands. In a local picture, this translates into a strongly reduced hybridization of nickel 3 d - and oxygen 2 p -orbitals with possibly important consequences for the magnetic superexchange interaction. Reduced hybridization reduces the effective hopping t between magnetic nickel ions by way of the oxygen ligand. Because the coupling constant J is proportional to t 2/ U , where U is the on-site Coulomb repulsion, values 10 times smaller than those in cuprates have been estimated ([ 3 ][3], [ 4 ][4]). Quantum chemical calculations ([ 5 ][5]), however, provide an alternative argument that both t and U are reduced in the nickelates. These calculations predict a superexchange coupling J = 77 meV for the bulk structure of NdNiO2, which is relatively close to the one reported by Lu et al. ![Figure][6] Superconducting nickelatesGRAPHIC: C. BICKEL/ SCIENCE A notable aspect of the authors' infinite-layer nickelate superconductors is that they are synthesized as epitaxial thin films grown on a single-crystalline SrTiO3 substrate. Neither superconductivity nor antiferromagnetic order have been observed in bulk samples ([ 6 ][7]). This calls into consideration the extent to which heteroepitaxial modifications from the substrate play a decisive role in phase stabilization. Effects to be considered are, for example, the biaxial lattice mismatch with the underlying substrate and possible structural and electronic reconstructions at the polar substrate-film interface ([ 7 ][8], [ 8 ][9]). Because the hopping integral depends inversely on some power of the distance between the ions, a shrinkage of the in-plane lattice as provided by the epitaxy with the underlying SrTiO3 substrate could increase the superexchange coupling. Should heteroepitaxial influences prove to be decisive, extremely interesting perspectives arise from this for a targeted modification of the electronic structure as well as the magnetic interactions and thus the possibility to stabilize superconductivity at higher temperatures. Addressing the coupling to rare-earth itinerant electrons will also need to be sorted out. This might be accomplished by examining the spin waves in the analogous lanthanum compound. The self-doped Ruddlesden-Popper natural superlattices with varying numbers of infinite-layer nickelate slabs are another possible material system for gaining insight into the electronic structure. A recent x-ray spectroscopy study found sizable antiferromagnetic superexchange but also indicates differences in nickel-oxygen hybridization ([ 9 ][10]). Further information on the symmetry of the superconducting wave function is desired to assess the possibility of a magnon-mediated Copper-pairing mechanism. High- T c cuprates show a characteristic d -wave symmetry of the superconducting gap function, which can be examined, for example, with scanning tunneling spectroscopy. 1. [↵][11]1. H. Lu et al ., Science 373, 213 (2021). [OpenUrl][12][Abstract/FREE Full Text][13] 2. [↵][14]1. D. Li et al ., Nature 572, 624 (2019). [OpenUrl][15][CrossRef][16][PubMed][17] 3. [↵][18]1. M. Jiang, 2. M. Berciu, 3. G. A. Sawatzky , Phys. Rev. Lett. 124, 207004 (2020). [OpenUrl][19][CrossRef][20][PubMed][21] 4. [↵][22]1. Z. Liu et al ., NPJ Quantum Mater. 5, 31 (2020). [OpenUrl][23][CrossRef][24] 5. [↵][25]1. V. M. Katukuri, 2. N. A. Bogdanov, 3. O. Weser, 4. J. van den Brink, 5. A. Alavi , Phys. Rev. B 102, 241112 (2020). [OpenUrl][26] 6. [↵][27]1. B.-X. Wang et al ., Phys. Rev. Mater. 4, 084409 (2020). [OpenUrl][28] 7. [↵][29]1. F. Bernardini, 2. A. Cano , J. Phys. Mat. 3, 03LT01 (2020). [OpenUrl][30] 8. [↵][31]1. B. Geisler, 2. R. Pentcheva , Phys. Rev. B102, 020502 (2020). [OpenUrl][32] 9. [↵][33]1. J. Q. Lin et al ., Phys. Rev. Lett. 126, 087001 (2021). [OpenUrl][34][CrossRef][35][PubMed][36] [1]: #ref-1 [2]: #ref-2 [3]: #ref-3 [4]: #ref-4 [5]: #ref-5 [6]: pending:yes [7]: #ref-6 [8]: #ref-7 [9]: #ref-8 [10]: #ref-9 [11]: #xref-ref-1-1 "View reference 1 in text" [12]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.aulast%253DLu%26rft.auinit1%253DH.%26rft.volume%253D373%26rft.issue%253D6551%26rft.spage%253D213%26rft.epage%253D216%26rft.atitle%253DMagnetic%2Bexcitations%2Bin%2Binfinite-layer%2Bnickelates%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.abd7726%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [13]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjEyOiIzNzMvNjU1MS8yMTMiO3M6NDoiYXRvbSI7czoyMjoiL3NjaS8zNzMvNjU1MS8xNTcuYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9 [14]: #xref-ref-2-1 "View reference 2 in text" [15]: {openurl}?query=rft.jtitle%253DNature%26rft.volume%253D572%26rft.spage%253D624%26rft_id%253Dinfo%253Adoi%252F10.1038%252Fs41586-019-1496-5%26rft_id%253Dinfo%253Apmid%252F31462797%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [16]: /lookup/external-ref?access_num=10.1038/s41586-019-1496-5&link_type=DOI [17]: /lookup/external-ref?access_num=31462797&link_type=MED&atom=%2Fsci%2F373%2F6551%2F157.atom [18]: #xref-ref-3-1 "View reference 3 in text" [19]: {openurl}?query=rft.jtitle%253DPhys.%2BRev.%2BLett.%26rft.volume%253D124%26rft.spage%253D207004%26rft_id%253Dinfo%253Adoi%252F10.1103%252FPhysRevLett.124.207004%26rft_id%253Dinfo%253Apmid%252F32501091%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [20]: /lookup/external-ref?access_num=10.1103/PhysRevLett.124.207004&link_type=DOI [21]: /lookup/external-ref?access_num=32501091&link_type=MED&atom=%2Fsci%2F373%2F6551%2F157.atom [22]: #xref-ref-4-1 "View reference 4 in text" [23]: {openurl}?query=rft.jtitle%253DNPJ%2BQuantum%2BMater.%26rft.volume%253D5%26rft.spage%253D31%26rft_id%253Dinfo%253Adoi%252F10.1038%252Fs41535-020-0229-1%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [24]: /lookup/external-ref?access_num=10.1038/s41535-020-0229-1&link_type=DOI [25]: #xref-ref-5-1 "View reference 5 in text" [26]: {openurl}?query=rft.jtitle%253DPhys.%2BRev.%2BB%26rft.volume%253D102%26rft.spage%253D241112%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [27]: #xref-ref-6-1 "View reference 6 in text" [28]: {openurl}?query=rft.jtitle%253DPhys.%2BRev.%2BMater.%26rft.volume%253D4%26rft.spage%253D084409%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [29]: #xref-ref-7-1 "View reference 7 in text" [30]: {openurl}?query=rft.jtitle%253DJ.%2BPhys.%2BMat.%26rft.volume%253D3%26rft.spage%253D03LT01%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [31]: #xref-ref-8-1 "View reference 8 in text" [32]: {openurl}?query=rft.jtitle%253DPhys.%2BRev.%26rft.volume%253D102%26rft.spage%253D020502%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [33]: #xref-ref-9-1 "View reference 9 in text" [34]: {openurl}?query=rft.jtitle%253DPhys.%2BRev.%2BLett.%26rft.volume%253D126%26rft.spage%253D087001%26rft_id%253Dinfo%253Adoi%252F10.1103%252FPhysRevLett.126.087001%26rft_id%253Dinfo%253Apmid%252F33709756%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [35]: /lookup/external-ref?access_num=10.1103/PhysRevLett.126.087001&link_type=DOI [36]: /lookup/external-ref?access_num=33709756&link_type=MED&atom=%2Fsci%2F373%2F6551%2F157.atom
领域	气候变化 ; 资源环境
URL	查看原文
引用统计
文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/334227
专题	气候变化资源环境科学
推荐引用方式 GB/T 7714	Eva Benckiser. A touch more unconventional[J]. Science,2021.
APA	Eva Benckiser.(2021).A touch more unconventional.Science.
MLA	Eva Benckiser."A touch more unconventional".Science (2021).