Large orbital polarization in a metallic square-planar nickelate

Zhang, Junjie; Botana, Antía S.; Freeland, J. W.; Phelan, Daniel; Zheng, Hong; Pardo, Víctor; Norman, M. R.; Mitchell, J. F.

doi:10.1038/nphys4149

Cited by 179 publications

(235 citation statements)

References 44 publications

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“…It should also be noted that in other nickelate compounds, nickel valence state reduction could be achieved from removing oxygen along with a significant change of the crystal structures, [33][34][35] which is not seen in our case. Further, we have found that when the rare-earth ion is large (for example, LaNiO 3 ), it is very challenging to modify the conductivity of the materials via our hydrogen doping method, [3] which is not the case in other studies.…”

Section: Wwwadvmatde Wwwadvancedsciencenewscommentioning

confidence: 59%

“…Further, we have found that when the rare-earth ion is large (for example, LaNiO 3 ), it is very challenging to modify the conductivity of the materials via our hydrogen doping method, [3] which is not the case in other studies. [33][34][35] So these observations indicate that we should encounter different mechanisms, and why such discrepancy exists currently remains unknown. Possible reasons include the use of different conditions or different parent materials (e.g., bulk ReNiO 3 vs Ruddlesden-Popper layered [35] ).…”

Section: Wwwadvmatde Wwwadvancedsciencenewscommentioning

confidence: 99%

“…[33][34][35] So these observations indicate that we should encounter different mechanisms, and why such discrepancy exists currently remains unknown. Possible reasons include the use of different conditions or different parent materials (e.g., bulk ReNiO 3 vs Ruddlesden-Popper layered [35] ). In addition, according to the recent discovery of superconductivity in reduced layered nickelate, such as Nd 0.8 Sr 0.2 NiO 2 , [36] a possible Sr-Sm intermixing in combination with oxygen vacancies at the interface between SrRuO 3 and SmNiO 3 may also influence electron configurations of the nickelate.…”

Section: Wwwadvmatde Wwwadvancedsciencenewscommentioning

confidence: 99%

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Electron‐Doping Mottronics in Strongly Correlated Perovskite

et al. 2019

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Hydrogen (proton) induced switchable multiphase transformations in d-band electron-correlated materials recently opened a new field for exploring merging multifunctional proton-gated electronic devices, [1] synaptic plasticity, [2,3] sensors, [4] and novel energy conversion devices. [5] Compared to other dopant elements, hydrogen is small in radius and has high ionic mobility. [1,[4][5][6] Therefore, the proton distribution is highly adjustable via external electric fields, and the respective tuning of the physical properties of materials is feasible. This is, in particular, the case for the hydrogen-induced sharp transitions in electron orbital configurations and the magnetoelectric/spintronic states for d-band electron-correlated materials, such as SmNiO 3 , [1][2][3][4][5] SrCoO 3−δ , [6] and VO 2 . [7] As a typical example, the hydrogenation of the perovskite-structured SmNiO 3 d-band electron-correlated system results in an abrupt electronic transition of the e g orbital from the electron-itinerant Ni 3+ t e 2g 6 g 1 state to the electron-localized Ni 2+ t e 2g 6 g 2 The discovery of hydrogen-induced electron localization and highly insulating states in d-band electron correlated perovskites has opened a new paradigm for exploring novel electronic phases of condensed matters and applications in emerging field-controlled electronic devices (e.g., Mottronics). Although a significant understanding of doping-tuned transport properties of single crystalline correlated materials exists, it has remained unclear how dopingcontrolled transport properties behave in the presence of planar defects. The discovery of an unexpected high-concentration doping effect in defective regions is reported for correlated nickelates. It enables electronic conductance by tuning the Fermi-level in Mott-Hubbard band and shaping the lower Hubbard band state into a partially filled configuration. Interface engineering and grain boundary designs are performed for H x SmNiO 3 /SrRuO 3 heterostructures, and a Mottronic device is achieved. The interfacial aggregation of hydrogen is controlled and quantified to establish its correlation with the electrical transport properties. The chemical bonding between the incorporated hydrogen with defective SmNiO 3 is further analyzed by the positron annihilation spectroscopy. The present work unveils new materials physics in correlated materials and suggests novel doping strategies for developing Mottronic and iontronic devices via hydrogen-doping-controlled orbital occupancy in perovskite heterostructures.

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Section: Wwwadvmatde Wwwadvancedsciencenewscommentioning

confidence: 59%

Section: Wwwadvmatde Wwwadvancedsciencenewscommentioning

confidence: 99%

Section: Wwwadvmatde Wwwadvancedsciencenewscommentioning

confidence: 99%

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Electron‐Doping Mottronics in Strongly Correlated Perovskite

et al. 2019

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Electronic structure of the parent compound of superconducting infinite-layer nickelates

et al. 2020

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The search for oxide materials with physical properties similar to the cuprate high Tc superconductors, but based on alternative transition metals such as nickel, has grown and evolved over time [1][2][3][4][5][6][7][8][9][10]. The recent discovery of superconductivity in doped infinite-layer nickelates RNiO2 (R = rare-earth element) [11,12] further strengthens these efforts. With a crystal structure similar to the infinite-layer cupratestransition metal oxide layers separated by a rare-earth spacer layerformal valence counting suggests that these materials have monovalent Ni 1+ cations with the same 3d electron count as Cu 2+ in the cuprates. Here, we use x-ray spectroscopy in concert with density functional theory to show that the electronic structure of RNiO2 (R = La, Nd), while similar to the cuprates, includes significant distinctions. Unlike cuprates with insulating spacer layers between the CuO2 planes, the rare-earth spacer layer in the infinite-layer nickelate supports a weaklyinteracting three-dimensional 5d metallic state. This three-dimensional metallic state hybridizes with a quasi-two-dimensional, strongly correlated state with 3dx 2 -y 2 symmetry in the NiO2 layers. Thus, the infinite-layer nickelate can be regarded as a sibling of the rare earth intermetallics [13-15], well-known for heavy Fermion behavior, where the NiO2 correlated layers play an analogous role to the 4f states in rare-earth heavy Fermion compounds. This unique Kondo-or Anderson-lattice-like "oxide-intermetallic" replaces the Mott insulator as the reference state from which superconductivity emerges upon doping.While the mechanism of superconductivity in the cuprates remains a subject of intense research, early on it was suggested that the conditions required for realizing high Tc superconductivity are rooted in the physics of a two-dimensional electron system subject to strong local repulsion [16,17]. This describes the Mott (charge-transfer) insulators in the stoichiometric parent compounds, characterized by spin ½ Heisenberg antiferromagnetism, from which superconductivity emerges upon doping. A long-standing question regards whether these "cuprate-Mott" conditions can be realized in other oxides; and extensive efforts to synthesize and engineer nickel oxides (nickelates) have promised such a realization [1-10]. Infinite-layer NdNiO2 became the first such nickelate superconductor following the recent discovery of superconductivity in Srdoped samples [11]. The undoped parent compound, produced by removing the apical oxygen atoms from the perovskite nickelate NdNiO3 using a metal hydride-based soft chemistry reduction process [10,[18][19][20], appears to be a close sibling of the cuprates-it is isostructural to the infinitelayer cuprates with monovalent Ni 1+ cations and possesses the same 3d 9 electron count as that of Cu 2+ cations in undoped cuprates. Yet, as we will reveal, the electronic structure of the undoped RNiO2 (R = La and Nd) remains distinct from the Mott, or charge-transfer, compounds of undoped cuprates, and even...

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“…electronic structure [12,13] . The infinite-layer materials RNiO2 (R = La, Nd) are one of the ideal systems to simulate cuprates.…”

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Absence of superconductivity in bulk Nd1−xSrxNiO2

et al. 2020

Commun Mater

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Recently superconductivity at 9 -15 K was discovered in an infinite-layer nickelate (Nd0.8Sr0.2NiO2 films), which has received enormous attention.Since the Ni 1+ ionic state in NdNiO2 may have the 3d 9 outer-shell electronic orbit which resembles that of the cuprates, it is very curious to know whether superconductivity discovered here has similar mechanism as that in the cuprates. By using a three-step method, we successfully synthesize the bulk samples of Nd1-xSrxNiO2 (x = 0, 0.2, 0.4). The X-ray diffractions reveal that all the samples contain mainly the infinite layer phase of 112 with some amount of segregated Ni. This has also been well proved by the SEM image and the EDS composition analysis. The resistive measurements on the Sr doped samples show insulating behavior without the presence of superconductivity. Temperature dependence of the magnetic moment under high magnetic fields exhibits a Curie-Weiss law feature with the paramagnetic moment of about 2B/f.u.. By applying pressure on Nd0.8Sr0.2NiO2 up to about 50.2 GPa, we find that the strong insulating behavior at ambient pressure is significantly suppressed, but superconductivity has not been observed either. Since the lattice constants derived from our XRD data are very close to those of the reported superconducting films, we argue that the superconductivity in the reported film may not originate from the expected Nd0.8Sr0.2NiO2, but arise from the interface or the stress effect.Since the discovery of high critical temperature superconductivity (HTS) in cuprates in 1986 [1] , there are plenty of experimental and theoretical studies to explore the intrinsic mechanism for superconductivity [2][3][4][5] . There is a general agreement that the parent compound of cuprates like La2CuO4 is a Mott insulator with a charge transfer gap and long-range antiferromagnetic (AF) order [6] . With chemical doping, the long-range AF order will be suppressed at a hole doping level (p  0.02) and d-wave superconductivity emerges at a higher doping level (p  0.05) [7][8][9] . After the efforts more than three decades, some common features have been observed, although the intrinsic pairing mechanism of HTS remains unresolved yet. These include two-dimensional electronic structure and coexistence with an AF order or spin fluctuations, all these also occur in most iron-based [10] and heavy fermion superconductors [11] .Moreover, in cuprates, it is also important that the spin S = 1/2 magnetic moment from 3d 9 electrons form the basic structure of the AF order. One intuitive way to explore the pairing mechanism of cuprates is to find additional high-TC superconductors with different transition metals but similar crystal and

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Large orbital polarization in a metallic square-planar nickelate

Cited by 179 publications

References 44 publications

Electron‐Doping Mottronics in Strongly Correlated Perovskite

Electron‐Doping Mottronics in Strongly Correlated Perovskite

Electronic structure of the parent compound of superconducting infinite-layer nickelates

Absence of superconductivity in bulk Nd1−xSrxNiO2

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