Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J48: Superconductivity: Nickelates |
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Sponsoring Units: DCMP Chair: Bing Lv, University of Texas at Dallas Room: Mile High Ballroom 1A |
Tuesday, March 3, 2020 2:30PM - 2:42PM |
J48.00001: The Superconducting Phase Diagram of the Infinite-Layer Nickelates Danfeng Li, Bai Yang Wang, Kyuho Lee, Motoki Osada, Berit Goodge, Lena Fitting Kourkoutis, Harold Hwang The recently discovered superconducting infinite-layer nickelate, Nd0.8Sr0.2NiO2 [1], provides an additional platform of studying the physics of the high-Tc superconductors in a cuprate-like system. The possible similarities and differences in the electronic structure to cuprates have been debated and attracted a lot of interest. One particular question among them is whether there is a “dome-shape” in the superconducting phase diagram of this new superconductor upon varying the Sr doping, analogous to that of cuprates. Here, we present a first study of such doping dependence of transition temperatures, lattice spacings as well as transport properties, to which controlling the crystallinity and nickel oxidation state across different dopings by our approaches to materials synthesis appears to be essential. |
Tuesday, March 3, 2020 2:42PM - 2:54PM |
J48.00002: Efforts to Synthesize Bulk Superconducting Infinite-Layer Nickelates:
R3Ni3O7 and Other Phases Prepared by Hydrogen Reduction of RNiO3* Gregorio Ponti, Quinn D. B. Timmers, Zachary P. Kuklinski, John Markert Recently, superconductivity in a nickelate was reported1 in an apparently hole-doped RNiO2 (“infinite-layer”) film (with R ≈ Nd0.8Sr0.2), after CaH2 reduction. We have prepared both parent and electron- and hole-doped specimens of the bulk, nearly simple-perovskite RNiO3 structures: R1–xAxNiO3 [R = Nd, Pr, (La,Y); A = Sr, Ce, Th] using high oxygen pressure (200 bar) at high temperatures (T ≈1000°C). We reduced these phases in several ways in an effort to produce bulk infinite-layer materials. For reduction in 5% H2 in Ar, and for T > 400°C, we find excess reduction to pure metal(s) or elemental oxides. But for temperatures in the range 300–375°C (reduction times of hours), we have synthesized a number of nickelate structures in bulk, dense form, suitable for transport and other measurements. One product is the “337” structure: R3Ni3O7. X-ray diffraction, electrical resistivity, magnetic, and other data indicate that n-doping (Ce4+) induces structural and electronic changes in the 337 material, and thus may provide an alternative path to “Ni2+/Ni1+” superconductivity. We also report other product phases and, thus, a rich reduced-nickelate phase diagram. |
Tuesday, March 3, 2020 2:54PM - 3:06PM |
J48.00003: Optimizing Synthesis of Superconducting Infinite-Layer Nickelates Kyuho Lee, Danfeng Li, Motoki Osada, Bai Yang Wang, Berit Goodge, Lena Fitting Kourkoutis, Harold Hwang Superconductivity was recently discovered in the infinite-layer nickelate Nd0.8Sr0.2NiO2.1 To proceed with further systematic studies in the superconducting properties of this material, it is important to establish a reproducible method to synthesize single-phase, single-crystalline Nd0.8Sr0.2NiO2. The synthetic route to this infinite-layer nickelate structure poses two major challenges. First, the precursor perovskite phase is difficult to stabilize due to the unusually high formal nickel valence of Ni+3.2 and the structural instability induced by chemical doping. Second, topochemical reduction on perovskite nickelates have shown limitations in coherent transition to the infinite-layer phase.2 After careful optimization, we have successfully established a reproducible method to stabilize Nd0.8Sr0.2NiO2 (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 structural and superconducting properties on growth conditions will be discussed. |
Tuesday, March 3, 2020 3:06PM - 3:18PM |
J48.00004: A superconducting praseodymium nickel oxide with infinite-layer structure Motoki Osada, Bai Yang Wang, Danfeng Li, Kyuho Lee, Berit Goodge, Lena Fitting Kourkoutis, Harold Hwang Nickel oxide compounds, which are analogous to copper oxides, have been intensively investigated in the past decades since the discovery of high-Tc superconductivity in copper oxides.1 The recent discovery of superconductivity in a neodymium nickel oxide of infinite-layer structure suggests the possible existence of a family of superconducting nickel oxide.2 Here, we present the synthesis of an infinite-layer praseodymium nickel oxide by topochemical reduction of the precursor perovskite thin films using calcium hydride as reagent. We report the observation of superconductivity with Tc of 9-12 K in such compound upon doping with strontium, Pr0.8Sr0.2NiO2. Details of the materials synthesis of the infinite-layer structure, measurements on temperature-dependence of resistivity and Hall coefficient will be discussed in this presentation. |
Tuesday, March 3, 2020 3:18PM - 3:30PM |
J48.00005: 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 recent discovery of superconductivity in Sr-doped NdNiO2 is an important development for condensed matter physics [1]. Nominally similar in structure to the infinite-layer cuprate superconductors, the nickelates present a complementary platform for investigating the underlying physical mechanisms driving superconductivity in these systems. The stabilization of superconducting samples is, however, as yet limited to thin film geometries, raising the importance of spatially localized characterization techniques capable of probing only the regions of interest without contributions from the substrate. Here, we harness the high spatial and energy resolution achieved with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) to explore both the lattice and electronic structure of these superconducting thin films. Structurally, the effects of different growth parameters are explored across several films within the nickelate series. Electronically, we investigate possible similarities to the cuprate superconductors. |
Tuesday, March 3, 2020 3:30PM - 3:42PM |
J48.00006: In Situ Synchrotron X-ray Studies of Nickelate Growth and Reduction YAN LI, XI YAN, Zhan Zhang, Hua Huan Wang, Hua Zhou, Dillon Fong
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Tuesday, March 3, 2020 3:42PM - 3:54PM |
J48.00007: Transport Characterization of Infinite Layer Nickelate Superconductor Bai Yang Wang, Danfeng Li, Kyuho Lee, Berit Goodge, Motoki Osada, Lena Fitting Kourkoutis, Harold Hwang The recently discovered infinite layer nickelate superconductor presents a potential new family of unconventional superconductors [1]. While sharing similar crystal structure with infinite layer cuprates, the electronic properties can be non-trivially distinct due to the relatively extreme valence state of Ni1+. DFT calculations have also pointed out potential involvement of multiple bands [2]. In this sense, a careful comparison against the cuprate system is imperative in obtaining a proper and unbiased view of the nickelate superconductivity. Furthermore, detailed characterization of the difference between the two systems 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. |
Tuesday, March 3, 2020 3:54PM - 4:06PM |
J48.00008: Electronic structure of the parent compound of superconducting infinite-layer nickelates Matthias Hepting, Danfeng Li, Chunjing Jia, Haiyu Lu, E. Pairs, Yi Tseng, X. Feng, Motoki Osada, Emily Been, Yasuyuki Hikita, Y. Chuang, Zahid Hussain, Kejin Zhou, A. Nag, Mirian Garcia-Fernandez, Matteo Rossi, Hsiao-Yu Huang, Di-Jing Huang, Zhixun Shen, Thorsten Schmitt, Harold Hwang, B. Moritz, Jan Zaanen, Thomas Devereaux, Wei-Sheng Lee Very recently, the first superconducting nickelate has been discovered, opening a new field of research. The novel superconductor is a Sr-doped infinite layer nickelate NdNiO2, which is isostructural to the infinite-layer cuprates and possesses the same nominal 3d electron count. Yet, it is important to experimentally characterize the electronic state of the parent compound from which the superconductivity emerges. In this presentation, we will present data of soft x-ray spectroscopy (XAS and RIXS) near the Ni L-edge and O K-edge on parent compound RNiO2 (R = La, Nd). Together with LDA + U calculations, the gross feature of the electronic structure and a low energy effective model for the infinite layer nickelate will be discussed. |
Tuesday, March 3, 2020 4:06PM - 4:18PM |
J48.00009: Doping evolution of the electronic structure of Sr-doped NdNiO2 Matteo Rossi, Haiyu Lu, Danfeng Li, Chunjing Jia, Emily Been, Y. Chuang, Kejin Zhou, Zhixun Shen, Brian Moritz, Thomas Devereaux, Harold Hwang, Wei-Sheng Lee Since the discovery of high-temperature superconductivity in cuprates, many efforts have been devoted to reproduce their electronic structure by proper material engineering. Nickel oxides occupy a prominent place since they are theoretically proposed to host superconductivity. After intense research, superconductivity has been recently discovered in Sr-doped NdNiO2. Theory and experiments have been conducted to understand the electronic structure of the parent compound NdNiO2. Yet, spectroscopic information about how Sr-doping affects the electronic states is still lacking. In this presentation, I will discuss the doping evolution of the electronic structure, as revealed by our recent experimental results from x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS). |
Tuesday, March 3, 2020 4:18PM - 4:30PM |
J48.00010: Exotic electronic structure in cuprate-like trilayer nickelate Pr4Ni3O8 Haoxiang Li, PEIPEI HAO, Kyle Gordon, Hong Zheng, Junjie Zhang, Xiaoqing Zhou, John Mitchell, Daniel Dessau As sharing similar layered structure and close electron configuration with the high-Tc cuprate superconductors, various series of nickel oxides have naturally become potential candidates for cuprate analogues. A previous study found a rare metallic state lying in the trilayer nickelate Pr4Ni3O8 (Pr438) with a quasi-2D lattice structure, which together with similar d-electron counting to the overly hole-doped cuprates and strong orbital polarization near the Fermi energy has drawn more attention to this compound[1]. Here we present a more direct and detailed study of the electronic structure of Pr438, with a combination of the Angle-resolved photoemission spectroscopy and Density-functional-theory calculations. Our spectroscopy data shows a non-gapped Fermi surface resembling the heavily hole-doped cuprates residing in the Fermi-liquid regime, bearing both electron- and hole-pockets, as has been corroborated by DFT calculations. These combine the predominant dx2-y2 feature and strong hybridization between the Ni-3d and O-2p states, rendering Pr438 an extraordinary analogue to cuprates, making it a promising host for superconductivity. |
Tuesday, March 3, 2020 4:30PM - 4:42PM |
J48.00011: Electronic Correlations in Nickelate Analogues of Cuprate Superconductors Jonathan Karp, Manuel Zingl, Antia S. Botana, Michael Norman, Andrew Millis Motivated by recent experiments on tri-layer (Pr4Ni3O8) and infinite layer (NdNiO2) analogues of cuprate superconductors, we use a combination of density functional and dynamical mean field (DFT+DMFT) methods to perform a comparative study of the metal-insulator and magnetic phase diagrams, many body electronic structure, and conduction band many-body mass enhancements of cuprate and nickelate materials. In the Ni materials the transition metal d-bands are more widely separated in energy from the O-p bands than in the cuprates, suggesting that the nickelates are more accurately modelled by a Hubbard model than are the cuprates. The role of Nd-derived d-bands in the physics of the nickelates is discussed and the possibility that in the nickelate case other Ni-d orbitals may be relevant is analyzed. Preliminary results on superconductivity within the DMFT approximation will be presented. |
Tuesday, March 3, 2020 4:42PM - 4:54PM |
J48.00012: Electronic Structure across the Rare-Earth Series in Superconducting Infinite Layer Nickelates Emily Been, Wei-Sheng Lee, Harold Hwang, Jan Zaanen, Thomas Devereaux, Brian Moritz, Chunjing Jia The exciting discovery of superconductivity in oxygen-reduced monovalent nickelates has raised a new platform for the study of unconventional superconductivity, with similarities and differences to the cuprate high temperature superconductors. General trends appear in the infinite nickelates RNiO2 with rare-earths R spanning across the Lanthanides. The role of oxygen charge transfer diminishes in comparison to the cuprates, with an increased and prominent role played by rare-earth 5d electrons near the Fermi level when traversing from La to Lu. A decrease in lattice volume indicates that the magnetic exchange additionally grows, which may be favorable for superconductivity. However, compensation effects from the itinerant 5d electrons presents a close analogy to Kondo or Anderson lattices, indicating a more complex interplay between charge transfer, bandwidth renormalization, compensation, and magnetic exchange. |
Tuesday, March 3, 2020 4:54PM - 5:06PM |
J48.00013: Hybridization and correlation effects in the electronic structure of infinite-layer nickelates Yuhao Gu, Sichen Zhu, xiaoxuan wang, Jiangping Hu, Hanghui Chen We combine density functional theory and dynamical mean field theory to study the electronic structure of infinite-layer nickelate NdNiO2. Without considering correlation effects on Ni, we find adjacent NiO2 planes are coupled by a metallic Nd spacer layer. However, the largest hybridization between Ni-dx2-y2 state and itinerant electrons origins from an interstitial-s orbital instead of Nd-d orbitals. Correlation effects on Ni reduces the hybridization between Ni-dx2-y2 state and itinerant electrons and when sufficiently strong, they can open a Mott gap, which is separated by the lower Hubbard band of Ni-dx2-y2 state and hybridization states (interstitial-s and Nd-d orbitals). With correlation strength increasing, antiferromagnetic ordering occurs before the metal-insulator transition. Experimentally long-range magnetic order has not been observed in NdNiO2. This places NdNiO2 in a paramagnetic metallic phase in which the hybridization between Ni-dx2-y2 and itinerant electrons is non-negligible and Ni correlation strength is moderate. |
Tuesday, March 3, 2020 5:06PM - 5:18PM |
J48.00014: Role of 4f states in superconducting nickelate Kwan-Woo Lee, Mi-Young Choi, Warren Pickett For a long time, condensed matter physicists have a question whether there may be nickelates that can host a cuprate-type superconductor. Very recently, NdNiO2 by 20%-Sr doping leads to superconducting up to Tc=15 K, while another most promising candidate LaNiO2 has never been superconducting. These discovery has been rejuvenated the long standing issue. In this presentation, we will focus on a primary distinction between NdNiO2 and LaNiO2. An obvious difference is that La3+ is closed shell and nonmagnetic, while Nd3+ with Hund’ rule ground state S=3/2, L=6, J=9/2 has a Curie-Weiss moment of about 3μB. Our results indicate that this magnetic interaction in Nd0.8Sr0.2NiO2 causes spin-disorder broadening of the Γ-centered Nd-driven electron Fermi surfaces and should be included in models of normal and superconducting states of Nd0.8Sr0.2NiO2 |
Tuesday, March 3, 2020 5:18PM - 5:30PM |
J48.00015: Doping-induced magnetic two-dimensionality and many-body electronic structure of superconducting infinite-layer nickelate Siheon Ryee, Hongkee Yoon, Taekjung Kim, Min Yong Jeong, Myung Joon Han To understand the superconductivity recently discovered in Nd1-xSrxNiO2, we carried out LDA+DMFT (local density approximation plus dynamical mean-field theory) and magnetic force response calculations. The on-site correlation in Ni-3d orbitals causes notable changes in the electronic structure. The calculated temperature-dependent susceptibility indicates the localized character of its spin moment. We also analyzed the low-frequency behavior of self-energy and resulting correlation strength. Remarkable new finding is that magnetic interactions in this material become two-dimensional by hole doping. While the undoped NdNiO2 has the sizable out-of-plane interaction, hole dopings strongly suppress it. This two-dimensionality is maximized at the hole concentration of δ ≈ 0.25. Further analysis as well as the implications of our new findings are presented. |
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