Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session R47: Superconductivity in NickelatesLive
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Sponsoring Units: DCMP Chair: Johanna Palmstrom, Stanford Univ |
Thursday, March 18, 2021 8:00AM - 8:12AM Live |
R47.00001: Strong Superexchange in a d9-δ Nickelate Revealed by Resonant Inelastic X-Ray Scattering Mark Dean, Pablo Villar Arribi, Gilberto F L Fabbris, Antia Botana, Derek J Meyers, Hu Miao, Yao Shen, Daniel Mazzone, Jiatai Feng, Sorin Gheorghe Chiuzbaian, Abhishek Nag, Andrew Walters, Mirian Garcia-Fernnandez, Ke-jin Zhou, Jonathan Pelliciari, Ignace Jarrige, John Freeland, Junjie Zhang, John Mitchell, Valentina Bisogni, xuerong Liu, Michael Ray Norman, Jiaqi Lin The discovery of superconductivity in a d9-δ nickelate has inspired disparate theoretical perspectives regarding the essential physics of this class of materials. A key issue is the magnitude of the magnetic superexchange, which relates to whether cuprate-like high-temperature nickelate superconductivity could be realized. We address this question using Ni L-edge and O K-edge spectroscopy of the reduced trilayer nickelate d9-1/3 La4Ni3O8 and associated theoretical modeling. A magnon energy scale of ~80 meV resulting from a nearest-neighbor magnetic exchange of J=69(4) meV is observed, proving that d9-δ nickelates can host a large superexchange. This value, along with that of the Ni-O hybridization estimated from our O K-edge data, implies that trilayer nickelates represent an intermediate case between the infinite-layer nickelates and the cuprates, and suggests that they represent a promising route towards higher-temperature nickelate superconductivity. |
Thursday, March 18, 2021 8:12AM - 8:24AM Live |
R47.00002: Atomic Lattice and Electronic Structure of Superconducting Nickelate Thin Films Berit Goodge, Danfeng Li, Kyuho Lee, Motoki Osada, Bai Yang Wang, Harold Hwang, Lena Fitting Kourkoutis The stabilization of superconducting infinite-layer nickelate thin films [1,2] presents a long-awaited platform for experimental comparison to the analogous cuprate superconductors and exploration of the underlying physical mechanisms. Unlike the bulk-synthesized cuprates, however, the thin film geometry of the superconducting nickelates motivates both structural and electronic characterization with high real-space resolution. Here, we harness atomic-scale scanning transmission electron microscopy (STEM) and localized electron energy loss spectroscopy (EELS) to explore both the lattice and electronic structure across a wide series of nickelate thin films. Combining high spatial and energy resolution, we spectroscopically reveal key electronic differences with the cuprate superconductors [3]. We also explore the role of the substrate with quantitative structural analysis. |
Thursday, March 18, 2021 8:24AM - 8:36AM Live |
R47.00003: Superconducting Dome and Electronic Structure of the Nickelate Superconductors Danfeng Li, Kyuho Lee, Bai Yang Wang, Motoki Osada, Shannon P. Harvey, Berit H. Goodge, Hye Ryoung Lee, Yasuyuki Hikita, Lena Fitting Kourkoutis, Harold Hwang The discovery of superconductivity in cuprates decades ago had stirred enduring interest in searching for analogous materials systems. In this talk, we present our observation of superconductivity in an infinite-layer nickelate thin film synthesized by a soft-chemistry approach1, and the study of its superconducting phase diagram2. This system is of particular interest due to its potential relationship with the high-Tc cuprate superconductors, in that they share a similar crystal structure and starting electronic configuration. We also highlight the key aspects of its electronic structure3, which turn out to be inherently distinct from cuprates, including the unusual role of Nd bands. |
Thursday, March 18, 2021 8:36AM - 8:48AM Live |
R47.00004: Penetration depth measurements of infinite-layer nickelates Shannon Harvey, Bai Yang Wang, Danfeng Li, Motoki Osada, Kyuho Lee, Varun Harbola, Samuel Crossley, Harold Hwang The discovery of superconductivity in infinite-layer nickelates [1] has the potential to help reveal the origins of high-temperature superconductivity. To do this, we must first develop an understanding of superconductivity in nickelates by measuring their fundamental properties. In this talk, I will present our measurements of the in-plane penetration depth of (Nd,Sr)NiO2 thin films across the doping-dependent superconducting dome [2]. The penetration depth provides information about the superfluid density and pairing symmetry of the superconducting state, both of which will be important in improving our understanding of the nature of superconductivity in these materials. |
Thursday, March 18, 2021 8:48AM - 9:00AM Live |
R47.00005: Transport Characterization of Infinite Layer Nickelate Superconductors Bai Yang Wang, Danfeng Li, Berit H. Goodge, Kyuho Lee, Motoki Osada, Shannon P. Harvey, Lena Fitting Kourkoutis, Malcolm R Beasley, Harold Hwang The recently discovered infinite layer nickelate superconductor presents a potential new family of unconventional superconductors [1]. A wide range of perspectives [2,3], emphasizing single- or multi-orbital electronic structure, Kondo or Hund’s coupling, and analogies to cuprates, have been proposed. Clearly, further experimental characterization of the superconducting state is needed to develop a foundational understanding of the nickelates. Furthermore, a detailed characterization of the difference between the nickelates and cuprates may provide new insights into the ingredients of superconductivity in layered oxide systems. As a step in this direction, we investigate and report the magnetotransport properties of nickelates in both the normal and superconducting state, with a focus on the anisotropic upper critical field. |
Thursday, March 18, 2021 9:00AM - 9:12AM Live |
R47.00006: Towards Higher-Crystallinity Superconducting Infinite-Layer Nickelates Kyuho Lee, Danfeng Li, Motoki Osada, Bai Yang Wang, Berit H. Goodge, Lena Fitting Kourkoutis, Harold Hwang The recent discovery of superconductivity in the infinite-layer nickelates Re1–xSrxNiO2 (Re = Nd, Pr)1,2 presents an important materials challenge to further improve the crystallinity and synthetic reproducibility of this difficult material,3,4 so that intrinsic investigations of the superconducting and normal-state properties of this system can be initiated. After careful optimization of the growth and reduction conditions, we have identified key parameters for further improving crystallinity and established a reproducible method to stabilize Nd1–xSrxNiO2 (001) epitaxial thin films on SrTiO3 (001) substrate by pulsed-laser deposition and CaH2-assisted topochemical reduction. The details of the optimization process and the dependence of the structural and superconducting properties on the growth conditions will be discussed. |
Thursday, March 18, 2021 9:12AM - 9:24AM Live |
R47.00007: Magnetic Excitations in Infinite-layer Nickelates Haiyu Lu, Matteo Rossi, Abhishek Nag, Motoki Osada, Danfeng Li, Bai Yang Wang, Mirian Garcia-Fernnandez, Stefano Agrestini, Zhixun Shen, Emily Been, Brian John Moritz, Thomas Devereaux, Jan Zaanen, Harold Hwang, Ke-jin Zhou, Wei-Sheng Lee The discovery of superconductivity in infinite-layer nickelates sparks a substantial amount of interest due to its similarities of crystal structure and nominal d-orbital valence to cuprates. One of the central questions regards whether magnetic excitations exist in infinite-layer nickelates and to what extend does it resemble the magnetic excitations in cuprates. Here, we studied the magnetic excitations in infinite-layer nickelates by resonant inelastic x-ray scattering (RIXS) at the Ni L3-edge. Signatures of magnetic excitations have been resolved. The behaviors of these excitations, their doping dependence, and the comparison with the magnetic excitations in cuprates will be discussed. |
Thursday, March 18, 2021 9:24AM - 9:36AM Live |
R47.00008: Spin dynamics in polycrystalline LaNiO2+δ Matthias Hepting, Roberto Ortiz, Pascal Puphal, Reinhard K. Kremer, Masahiko Isobe, Bernhard Keimer The decades-long quest for materials that mimic key properties of high-Tc superconducting cuprates has recently culminated in the discovery of superconductivity in Sr-doped infinite-layer (IL) nickelates [1]. However, first spectroscopic studies of the electronic structure [2] and orbital character [3] revealed several differences between cuprates and IL nickelates. Moreover, early experiments on polycrystalline powders of undoped IL nickelates reported a lack of long-range antiferromagnetic order, which is a hallmark of undoped cuprates. To shed new light on the magnetic correlations in IL nickelates, we have measured the dc and ac magnetic susceptibility of LaNiO2+δ powder, which was obtained from topotactically reduced LaNiO3. We find that gradual reduction towards the stoichiometric LaNiO2 phase leads to a strong enhancement of the susceptibility with emerging signatures of spin glass-like dynamics. The glassy behavior is partly reminiscent of the spin glass phase of lightly-doped cuprates and can arise from disorder, impurities, or possibly an intrinsic origin. |
Thursday, March 18, 2021 9:36AM - 9:48AM Live |
R47.00009: Magnetic exchange coupling in theoretically-designed cuprate-analog d9 nickelates Yusuke Nomura, Takuya Nomoto, Motoaki Hirayama, Ryotaro Arita Motivated by the discovery of superconductivity in doped nickelate R1-xSrxNiO2 (R=Nd, Pr), we study the magnetic exchange coupling J in layered d9 nickelates, which would serve as cuprate-analog materials in the Mott-Hubbard regime. The mother compounds of the cuprates are a charge-transfer-type Mott insulator, and the J value reaches as large as about 130 meV. The large J is a unique feature of the cuprates and might play a role in realizing the high-Tc superconductivity. It is interesting to investigate whether the Mott-Hubbard-type d9 nickelates can also have a large J. However, one complexity is that RNiO2 (R=Nd, Pr) is not a Mott insulator due to carrier doping from the rare-earth layer [1]. To compare the cuprates and d9 nickelates on an equal footing, we study theoretically-designed RbCa2NiO3 and A2NiO2Br2 (A: a cation with the valence of 2.5+). These nickelates are free from the self-doping, and the Ni x2-y2 orbital becomes half-filled [2]. We show that these nickelates have a significant J as large as about 100 meV, which is not far smaller than that of the cuprates [3]. |
Thursday, March 18, 2021 9:48AM - 10:00AM Live |
R47.00010: Orbital and spin character of doped carriers in infinite-layer nickelates Matteo Rossi, Haiyu Lu, Abhishek Nag, Danfeng Li, Motoki Osada, Kyuho Lee, Bai Yang Wang, Stefano Agrestini, Mirian Garcia-Fernnandez, Yi-De Chuang, Zhixun Shen, Harold Hwang, Brian John Moritz, Ke-jin Zhou, Thomas Devereaux, Wei-Sheng Lee The recent discovery of superconductivity in Sr-doped infinite-layer NdNiO2 [1] has sparked significant interest in condensed matter physics. The search of superconductivity in nickel oxides was inspired by mimicking some of the essential characteristics of cuprates, such as the layered crystal structure and nominal 3d9 valence configuration [2]. Yet, some distinctions emerge including large charge-transfer energy and presence of small electron pockets from rare-earth 5d orbitals [3,4]. At this early stage, a key open question is the evolution of the electronic structure with doping. The competition between electron correlation, charge-transfer energy, crystal field splitting and Hund’s exchange may give rise to different scenarios, where doped holes could be introduced into Ni (in a high- or low-spin state), O or Nd bands. Here, we use a combination of x-ray absorption spectroscopy (XAS), resonant inelastic x-ray scattering (RIXS) and multiplet calculations to determine the dominant configuration of doped holes in Nd1-xSrxNiO2. |
Thursday, March 18, 2021 10:00AM - 10:12AM Live |
R47.00011: A substantial hybridization between correlated Ni-d orbital and itinerant electrons in infinite-layer nickelates Yin Zhou, Yuhao Gu, sichen zhu, Xiaoxuan Wang, Jiangping Hu, Hanghui Chen The discovery of unconventional superconductivity in hole-doped NdNiO2, similar to CaCuO2, has received enormous attention. However, different from CaCuO2, NdNiO2 and LaNiO2 has itinerant electrons in the rare-earth spacer layer. Previous studies show that the hybridization between Ni-����2−��2 and rare-earth-d orbitals is very weak and thus RNiO2 is still a promising analog of CaCuO2. Here, we perform first-principles calculations to show that the hybridization between Ni-����2−��2 orbital and itinerant electrons in RNiO2 are substantially stronger than previously thought. The dominant hybridization comes from an interstitial-s orbital rather than rare-earth-d orbitals, due to a large inter-cell hopping. Because of the hybridization, Ni local moment is screened by itinerant electrons, the antiferromagnetic fluctuation is suppressed and the critical UNi to stabilize a long-range magnetic ordering is increased. Our work shows that the electronic structure of RNiO2 is distinct from CaCuO2, implying that the observed superconductivity in infinite-layer nickelates does not emerge from a doped Mott insulator. |
Thursday, March 18, 2021 10:12AM - 10:24AM Live |
R47.00012: Superconducting Praseodymium Nickelate Thin Films via a Soft Chemistry Approach Motoki Osada, Bai Yang Wang, Shannon Harvey, Berit H. Goodge, Kyuho Lee, Danfeng Li, Lena Fitting Kourkoutis, Harold Hwang A variety of nickel oxide compounds have long been studied for their manifestation of various correlated electron phenomena due to their analogous electronic or atomic structure to cuprates. Recently, superconductivity was observed in nanoscale infinite layer nickelate thin films of Nd0.8Sr0.2NiO2, epitaxially stabilized on SrTiO3 substrates via topotactic reduction from the perovskite precursor phase [1-4]. Here we present the synthesis and properties of PrNiO2 thin films on SrTiO3. Upon doping in Pr0.8Sr0.2NiO2, we observe superconductivity with a transition temperature of 7-12 K, and robust critical current density at 2 K of 334 kA/cm2 [5]. These findings indicate that superconductivity in the infinite layer nickelates is relatively insensitive to the details of the rare earth 4f configuration. Furthermore, they motivate the exploration of a broader family of compounds based on two-dimensional NiO2 planes. |
Thursday, March 18, 2021 10:24AM - 10:36AM Live |
R47.00013: Synthesis and characterization of infinite-layer La1-xCaxNiO2 single crystals Pascal Puphal, Yu-Mi Wu, Hangoo Lee, Katrin Fuersich, Roberto Ortiz, Matteo Minola, Y. Eren Suyolcu, Peter A. van Aken, Bernhard Keimer, Masahiko Isobe, Matthias Hepting Superconductivity was recently discovered in Sr-doped RNiO2 (R = Pr, Nd) thin films. However, first experiments on polycrystalline powder samples reveal no superconducting transition, raising the question whether epitaxy to a substrate is required for superconductivity in nickelates. So far, high-quality bulk single-crystalline samples have not been investigated, although they might host properties distinct from powders. We have therefore synthesized perovskite nickelate single crystals with various rare-earth cations R and dopant elements using flux growth under high pressure via a Walker-type multi-anvil apparatus. We found that especially the compound La0.8Ca0.2NiO3 can be synthesized with excellent crystalline quality and without traceable impurity phases. We will present the synthesis of La0.8Ca0.2NiO3 and the reduction to La0.8Ca0.2NiO2, together with results from scanning transmission electron microscopy, x-ray diffraction, magnetic susceptibility, electronic transport, and Raman spectroscopy measurements. |
Thursday, March 18, 2021 10:36AM - 10:48AM On Demand |
R47.00014: Tuning carrier density via magnetic correlations in NdNiO$_2$: a practical mean to resolve the nature of hole carriers Ruoshi Jiang, Zijian Lang, Tom Berlijn, Wei Ku Recently discovered unconventional superconductor Nd$_{0.8}$Sr$_{0.2}$NiO$_2$ demonstrated many traits similar to the prototypical cuprates. Yet, density functional theory (DFT) calculations suggest two noticeable differences: existence of electron carriers in Nd-$d$ orbitals, and potential importance of Ni-$d_{z^2} orbital in hosting hole carriers. Here, we examine the impacts of in-plane and out-of-plane magnetic correlations on the DFT+$U$ electronic structures, under various non-collinear thermal fluctuation. Our results demonstrate strong tuning of the kinetic energy of the key orbitals of Nd, Ni, and O, resulting a dramatic modification of carrier density. In contrast, such sensitivity to magnetic correlation should be absence in the competing many-body picture of singlet formation. Therefore, this effect points to sensitive experimental means to verify (or falsify) the current theoretical debate on the nature of the hole carriers in this system, for example via uniaxial pressure. |
Thursday, March 18, 2021 10:48AM - 11:00AM On Demand |
R47.00015: Where do the hole carriers reside in the new superconducting nickelates? Zijian Lang, Ruoshi Jiang, Wei Ku The families of high-temperature superconductors recently welcome a new member: hole doped nickelate Nd0.8Sr0.2NiO2 with a ~15K transition temperature. |
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