The Experts below are selected from a list of 1578 Experts worldwide ranked by ideXlab platform
Shriram Ramanathan - One of the best experts on this subject based on the ideXlab platform.
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Zero-differential thermal emission using thermochromic samarium Nickelate
2017 Conference on Lasers and Electro-Optics (CLEO), 2017Co-Authors: Patrick Roney, Shriram Ramanathan, Alireza Shahsafi, Zhen Zhang, You Zhou, Raymond Wambold, Jad Salman, Mikhail A. KatsAbstract:We demonstrate a thermal emitter whose radiated power remains nearly constant over a temperature range of δT ~ 30 °C, implemented using thermochromic samarium Nickelate. This zero-differential thermal emitter can be used for infrared camouflage and obfuscation.
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neuromimetic circuits with synaptic devices based on strongly correlated electron systems
Physical review applied, 2014Co-Authors: Jian Shi, Yasmine Meroz, L Mahadevan, Shriram RamanathanAbstract:Strongly correlated electron systems such as the rare-earth Nickelates (RNiO3, R denotes a rare-earth element) can exhibit synapselike continuous long-term potentiation and depression when gated with ionic liquids; exploiting the extreme sensitivity of coupled charge, spin, orbital, and lattice degrees of freedom to stoichiometry. We present experimental real-time, device-level classical conditioning and unlearning using Nickelate-based synaptic devices in an electronic circuit compatible with both excitatory and inhibitory neurons. We establish a physical model for the device behavior based on electric-field-driven coupled ionic-electronic diffusion that can be utilized for design of more complex systems. We use the model to simulate a variety of associate and nonassociative learning mechanisms, as well as a feedforward recurrent network for storing memory. Our circuit intuitively parallels biological neural architectures, and it can be readily generalized to other forms of cellular learning and extinction. The simulation of neural function with electronic device analogs may provide insight into biological processes such as decision making, learning, and adaptation, while facilitating advanced parallel information processing in hardware.
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neuromimetic circuits with synaptic devices based on strongly correlated electron systems
arXiv: Strongly Correlated Electrons, 2014Co-Authors: Jian Shi, Yasmine Meroz, L Mahadevan, Shriram RamanathanAbstract:Strongly correlated electron systems such as the rare-earth Nickelates (RNiO3, R = rare-earth element) can exhibit synapse-like continuous long term potentiation and depression when gated with ionic liquids; exploiting the extreme sensitivity of coupled charge, spin, orbital, and lattice degrees of freedom to stoichiometry. We present experimental real-time, device-level classical conditioning and unlearning using Nickelate-based synaptic devices in an electronic circuit compatible with both excitatory and inhibitory neurons. We establish a physical model for the device behavior based on electric-field driven coupled ionic-electronic diffusion that can be utilized for design of more complex systems. We use the model to simulate a variety of associate and non-associative learning mechanisms, as well as a feedforward recurrent network for storing memory. Our circuit intuitively parallels biological neural architectures, and it can be readily generalized to other forms of cellular learning and extinction. The simulation of neural function with electronic device analogues may provide insight into biological processes such as decision making, learning and adaptation, while facilitating advanced parallel information processing in hardware.
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colossal resistance switching and band gap modulation in a perovskite Nickelate by electron doping
Nature Communications, 2014Co-Authors: Jian Shi, You Zhou, Shriram RamanathanAbstract:Orbital occupancy by electrons has a large effect on electronic properties of correlated oxides. Here, the authors report a chemical doping strategy of a perovskite Nickelate, leading to the observation of a new insulating phase and a reversible resistivity modulation greater than eight orders of magnitude.
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conductivity noise study of the insulator metal transition and phase coexistence in epitaxial samarium Nickelate thin films
Physical Review B, 2014Co-Authors: Anindita Sahoo, Shriram Ramanathan, Arindam GhoshAbstract:Interaction between the lattice and the orbital degrees of freedom not only makes rare-earth Nickelates unusually ``bad metal,'' but also introduces a temperature-driven insulator-metal phase transition. Here we investigate this insulator-metal phase transition in thin films of SmNiO3 using the slow time-dependent fluctuations (noise) in resistivity. The normalized magnitude of noise is found to be extremely large, being nearly eight orders of magnitude higher than thin films of common disordered metallic systems, and indicates electrical conduction via classical percolation in a spatially inhomogeneous medium. The higher-order statistics of the fluctuations indicate a strong non-Gaussian component of noise close to the transition, attributing the inhomogeneity to the coexistence of the metallic and insulating phases. Our experiment offers insight into the impact of lattice-orbital coupling on the microscopic mechanism of electron transport in the rare-earth Nickelates.
Ryotaro Arita - One of the best experts on this subject based on the ideXlab platform.
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Nickelate superconductors a renaissance of the one band hubbard model
npj Quantum Materials, 2020Co-Authors: Motoharu Kitatani, Oleg Janson, Ryotaro Arita, Zhicheng Zhong, K HeldAbstract:The recently discovered Nickelate superconductors appear, at first glance, to be even more complicated multi-orbital systems than cuprates. To identify the simplest model describing the Nickelates, we analyse the multi-orbital system and find that it is instead the Nickelates which can be described by a one-band Hubbard model, albeit with an additional electron reservoir and only around the superconducting regime. Our calculations of the critical temperature TC are in good agreement with experiment, and show that optimal doping is slightly below 20% Sr-doping. Even more promising than 3d Nickelates are 4d palladates.
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Nickelate superconductors a renaissance of the one band hubbard model
arXiv: Superconductivity, 2020Co-Authors: Motoharu Kitatani, Oleg Janson, Ryotaro Arita, Zhicheng Zhong, K HeldAbstract:Following the discovery of superconductivity in the cuprates and the seminal work by Anderson, the theoretical efforts to understand high-temperature superconductivity have been focusing to a large extent on a simple model: the one-band Hubbard model. However, superconducting cuprates need to be doped, and the doped holes go into the oxygen orbitals. This requires a more elaborate multi-band model such as the three-orbital Emery model. The recently discovered Nickelate superconductors appear, at first glance, to be even more complicated multi-orbital systems. Here, we analyse this multi-orbital system and find that it is instead the Nickelates which can be described by a one-band Hubbard model, albeit with an additional electron reservoir and only around the superconducting regime. Our calculations of the critical temperature Tc are in good agreement with experiment, and show that optimal doping is slightly below the 20% Sr-doping of Ref. 11. Even more promising than 3d Nickelates are 4d palladates.
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formation of a two dimensional single component correlated electron system and band engineering in the Nickelate superconductor ndnio 2
Physical Review B, 2019Co-Authors: Yusuke Nomura, Motoaki Hirayama, Terumasa Tadano, Yoshihide Yoshimoto, Kazuma Nakamura, Ryotaro AritaAbstract:Motivated by the discovery of the Nickelate superconductor Nd${}_{0.8}$Sr${}_{0.2}$NiO${}_{2}$, the authors construct an effective low-energy Hamiltonian for the parent compound NdNiO${}_{2}$, which is found to be strongly correlated. While high-T${}_{c}$ superconductivity emerges near the Mott-insulating phase in the cuprates, NdNiO${}_{2}$ is not a Mott insulator, because the 3$d$ ${x}^{2}$-${y}^{2}$ band of nickel is self-doped. The authors propose a route for the design of novel Nickelates where self-doping is suppressed. If synthesized, such Nickelates would provide a playground for the exploration of high-T${}_{c}$ superconductivity.
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orbital characters of three dimensional fermi surfaces in eu 2 x sr x nio 4 as probed by soft x ray angle resolved photoemission spectroscopy
Physical Review B, 2011Co-Authors: Masaki Uchida, Ryotaro Arita, K Ishizaka, P Hansmann, Y Kaneko, Xiaoping Yang, M Sakano, Jun Miyawaki, Y Takata, M OuraAbstract:The three-dimensional Fermi-surface structure of hole-doped metallic layered Nickelate Eu${}_{2\ensuremath{-}x}$Sr${}_{x}$NiO${}_{4}$ ($x=1.1$), an important counterpart to the isostructural superconducting cuprate La${}_{2\ensuremath{-}x}$Sr${}_{x}$CuO${}_{4}$, is investigated by energy-dependent soft-x-ray angle-resolved photoemission spectroscopy. In addition to a large cylindrical hole Fermi surface analogous to the cuprates, we observe a $\ensuremath{\Gamma}$-centered $3{z}^{2}\ensuremath{-}{r}^{2}$-derived small electron pocket. This finding demonstrates that in the layered Nickelate the $3{z}^{2}\ensuremath{-}{r}^{2}$ band resides close to the ${x}^{2}\ensuremath{-}{y}^{2}$ one in energy. The resultant multiband feature with varying orbital character as revealed may strongly work against the emergence of the high-temperature superconductivity.
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pseudogap of metallic layered Nickelate r 2 x sr x nio 4 r nd eu crystals measured using angle resolved photoemission spectroscopy
Physical Review Letters, 2011Co-Authors: Masaki Uchida, K Ishizaka, P Hansmann, Y Kaneko, Y Ishida, Xiaohu Yang, Reiji Kumai, A Toschi, Y Onose, Ryotaro AritaAbstract:We have investigated charge dynamics and electronic structures for single crystals of metallic layered Nickelates, R(2-x)Sr(x)NiO4 (R = Nd, Eu), isostructural to La(2-x)Sr(x)CuO4. Angle-resolved photoemission spectroscopy on the barely metallic Eu(0.9)Sr(1.1)NiO4 (R = Eu, x = 1.1) has revealed a large hole surface of x2-y2 character with a high-energy pseudogap of the same symmetry and comparable magnitude with those of underdoped (x<0.1) cuprates, although the antiferromagnetic interactions are 1 order of magnitude smaller. This finding strongly indicates that the momentum-dependent pseudogap feature in the layered Nickelate arises from the real-space charge correlation.
Junjie Zhang - One of the best experts on this subject based on the ideXlab platform.
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intertwined density waves in a metallic Nickelate
Nature Communications, 2020Co-Authors: Antia S Botana, Junjie Zhang, Daniel Phelan, Yusheng Chen, Hong Zheng, Matthew Krogstad, Suyin Grass Wang, Y Qiu, J A RodriguezriveraAbstract:Nickelates are a rich class of materials, ranging from insulating magnets to superconductors. But for stoichiometric materials, insulating behavior is the norm, as for most late transition metal oxides. Notable exceptions are the 3D perovskite LaNiO3, an unconventional paramagnetic metal, and the layered Ruddlesden-Popper phases R4Ni3O10, (R = La, Pr, Nd). The latter are particularly intriguing because they exhibit an unusual metal-to-metal transition. Here, we demonstrate that this transition results from an incommensurate density wave with both charge and magnetic character that lies closer in its behavior to the metallic density wave seen in chromium metal than the insulating stripes typically found in single-layer Nickelates like La2-xSrxNiO4. We identify these intertwined density waves as being Fermi surface-driven, revealing a novel ordering mechanism in this Nickelate that reflects a coupling among charge, spin, and lattice degrees of freedom that differs not only from the single-layer materials, but from the 3D perovskites as well. Layered Ruddlesden-Popper structure Nickelates R4Ni3O10 (R = La,Pr) show an unusual metal-to-metal transition, but its origin has remained elusive for more than two decades. Here, the authors show that this transition results from intertwined density waves that arise from a coupling between charge and spin degrees of freedom
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spin stripe order in a square planar trilayer Nickelate
Physical Review Letters, 2019Co-Authors: Antia S Botana, Junjie Zhang, Hong Zheng, J A Rodriguezrivera, Daniel M Pajerowski, L W Harriger, J P C RuffAbstract:Trilayer Nickelates, which exhibit a high degree of orbital polarization combined with an electron count (${d}^{8.67}$) corresponding to overdoped cuprates, have been identified as a promising candidate platform for achieving high-${T}_{c}$ superconductivity. One such material, ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{8}$, undergoes a semiconductor-insulator transition at $\ensuremath{\sim}105\text{ }\text{ }\mathrm{K}$, which was recently shown to arise from the formation of charge stripes. However, an outstanding issue has been the origin of an anomaly in the magnetic susceptibility at the transition and whether it signifies the formation of spin stripes akin to single layer Nickelates. Here we report single crystal neutron diffraction measurements (both polarized and unpolarized) that establish that the ground state is indeed magnetic. The ordering is modeled as antiferromagnetic spin stripes that are commensurate with the charge stripes, the magnetic ordering occurring in individual trilayers that are essentially uncorrelated along the crystallographic $c$ axis. A comparison of the charge and spin stripe order parameters reveals that, in contrast to single-layer Nickelates such as ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{NiO}}_{4}$ as well as related quasi-2D oxides including manganites, cobaltates, and cuprates, these orders uniquely appear simultaneously, thus demonstrating a stronger coupling between spin and charge than in these related low-dimensional correlated oxides.
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fermiology and electron dynamics of trilayer Nickelate la4ni3o10
Nature Communications, 2017Co-Authors: Xiaoqing Zhou, Thomas Nummy, Junjie Zhang, Victor Pardo, W E Pickett, J F Mitchell, D S DessauAbstract:Layered Nickelates have the potential for exotic physics similar to high T C superconducting cuprates as they have similar crystal structures and these transition metals are neighbors in the periodic table. Here we present an angle-resolved photoemission spectroscopy (ARPES) study of the trilayer Nickelate La4Ni3O10 revealing its electronic structure and correlations, finding strong resemblances to the cuprates as well as a few key differences. We find a large hole Fermi surface that closely resembles the Fermi surface of optimally hole-doped cuprates, including its [Formula: see text] orbital character, hole filling level, and strength of electronic correlations. However, in contrast to cuprates, La4Ni3O10 has no pseudogap in the [Formula: see text] band, while it has an extra band of principally [Formula: see text] orbital character, which presents a low temperature energy gap. These aspects drive the Nickelate physics, with the differences from the cuprate electronic structure potentially shedding light on the origin of superconductivity in the cuprates.Exploration of the electronic structure of Nickelates with similar crystal structure to cuprates may shed a light on the origin of high T c superconductivity. Here, Li et al. report strong resemblances and key differences of the electronic structure of trilayer Nickelate La4Ni3O10 compared to the cuprate superconductors.
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stacked charge stripes in the quasi 2d trilayer Nickelate la4ni3o8
Proceedings of the National Academy of Sciences of the United States of America, 2016Co-Authors: Junjie Zhang, Yusheng Chen, Hong Zheng, D Phelan, Michael R Norman, J F MitchellAbstract:Abstract The quasi-2D Nickelate La4Ni3O8 (La-438), consisting of trilayer networks of square planar Ni ions, is a member of the so-called T′ family, which is derived from the Ruddlesden–Popper (R-P) parent compound La4Ni3O10−x by removing two oxygen atoms and rearranging the rock salt layers to fluorite-type layers. Although previous studies on polycrystalline samples have identified a 105-K phase transition with a pronounced electronic and magnetic response but weak lattice character, no consensus on the origin of this transition has been reached. Here, we show using synchrotron X-ray diffraction on high-pO2 floating zone-grown single crystals that this transition is associated with a real space ordering of charge into a quasi-2D charge stripe ground state. The charge stripe superlattice propagation vector, q = (2/3, 0, 1), corresponds with that found in the related 1/3-hole doped single-layer R-P Nickelate, La5/3Sr1/3NiO4 (LSNO-1/3; Ni2.33+), with orientation at 45° to the Ni-O bonds. The charge stripes in La-438 are weakly correlated along c to form a staggered ABAB stacking that reduces the Coulomb repulsion among the stripes. Surprisingly, however, we find that the charge stripes within each trilayer of La-438 are stacked in phase from one layer to the next, at odds with any simple Coulomb repulsion argument.
Raymond Fresard - One of the best experts on this subject based on the ideXlab platform.
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magnetic ordering in the striped Nickelate la5 3sr1 3nio4 a band structure point of view
EPL, 2008Co-Authors: U Schwingenschlogl, C Schuster, Raymond FresardAbstract:We report on a comprehensive study of the electronic and magnetic structure of the striped Nickelate La5/3Sr1/3NiO4. The investigation is carried out using band structure calculations based on the density functional theory. A magnetic structure compatible with experiment is obtained from spin-polarized calculations within the generalized gradient approximation (GGA), whereas inclusion of a local Coulomb interaction in the LDA+U framework results in a different ground state. The influence of the various interaction parameters is discussed in detail.
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magnetic ordering in the striped Nickelate la5 3sr1 3nio4 a band structure point of view
arXiv: Strongly Correlated Electrons, 2007Co-Authors: U Schwingenschlogl, C Schuster, Raymond FresardAbstract:We report on a comprehensive study of the electronic and magnetic structure of the striped Nickelate La5/3Sr1/3NiO4. The investigation is carried out using band structure calculations based on density functional theory. A magnetic structure compatible with experiment is obtained from spin-polarized calculations within the generalized gradient approximation (GGA), whereas inclusion of a local Coulomb interaction in the LDA+U framework results in a different ground state. The influence of the various interaction parameters is discussed in detail.
P Hansmann - One of the best experts on this subject based on the ideXlab platform.
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orbital characters of three dimensional fermi surfaces in eu 2 x sr x nio 4 as probed by soft x ray angle resolved photoemission spectroscopy
Physical Review B, 2011Co-Authors: Masaki Uchida, Ryotaro Arita, K Ishizaka, P Hansmann, Y Kaneko, Xiaoping Yang, M Sakano, Jun Miyawaki, Y Takata, M OuraAbstract:The three-dimensional Fermi-surface structure of hole-doped metallic layered Nickelate Eu${}_{2\ensuremath{-}x}$Sr${}_{x}$NiO${}_{4}$ ($x=1.1$), an important counterpart to the isostructural superconducting cuprate La${}_{2\ensuremath{-}x}$Sr${}_{x}$CuO${}_{4}$, is investigated by energy-dependent soft-x-ray angle-resolved photoemission spectroscopy. In addition to a large cylindrical hole Fermi surface analogous to the cuprates, we observe a $\ensuremath{\Gamma}$-centered $3{z}^{2}\ensuremath{-}{r}^{2}$-derived small electron pocket. This finding demonstrates that in the layered Nickelate the $3{z}^{2}\ensuremath{-}{r}^{2}$ band resides close to the ${x}^{2}\ensuremath{-}{y}^{2}$ one in energy. The resultant multiband feature with varying orbital character as revealed may strongly work against the emergence of the high-temperature superconductivity.
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pseudogap of metallic layered Nickelate r 2 x sr x nio 4 r nd eu crystals measured using angle resolved photoemission spectroscopy
Physical Review Letters, 2011Co-Authors: Masaki Uchida, K Ishizaka, P Hansmann, Y Kaneko, Y Ishida, Xiaohu Yang, Reiji Kumai, A Toschi, Y Onose, Ryotaro AritaAbstract:We have investigated charge dynamics and electronic structures for single crystals of metallic layered Nickelates, R(2-x)Sr(x)NiO4 (R = Nd, Eu), isostructural to La(2-x)Sr(x)CuO4. Angle-resolved photoemission spectroscopy on the barely metallic Eu(0.9)Sr(1.1)NiO4 (R = Eu, x = 1.1) has revealed a large hole surface of x2-y2 character with a high-energy pseudogap of the same symmetry and comparable magnitude with those of underdoped (x<0.1) cuprates, although the antiferromagnetic interactions are 1 order of magnitude smaller. This finding strongly indicates that the momentum-dependent pseudogap feature in the layered Nickelate arises from the real-space charge correlation.
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pseudogap of metallic layered Nickelate r 2 x sr x nio 4 r nd eu crystals measured using angle resolved photoemission spectroscopy
Physical Review Letters, 2011Co-Authors: Masaki Uchida, K Ishizaka, P Hansmann, Y Kaneko, Y Ishida, Xiaohu Yang, Reiji Kumai, A Toschi, Y Onose, Ryotaro AritaAbstract:We have investigated charge dynamics and electronic structures for single crystals of metallic layered Nickelates, ${R}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{NiO}}_{4}$ ($R=\mathrm{Nd},\mathrm{Eu}$), isostructural to ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$. Angle-resolved photoemission spectroscopy on the barely metallic ${\mathrm{Eu}}_{0.9}{\mathrm{Sr}}_{1.1}{\mathrm{NiO}}_{4}$ ($R=\mathrm{Eu}$, $x=1.1$) has revealed a large hole surface of ${x}^{2}\ensuremath{-}{y}^{2}$ character with a high-energy pseudogap of the same symmetry and comparable magnitude with those of underdoped ($xl0.1$) cuprates, although the antiferromagnetic interactions are 1 order of magnitude smaller. This finding strongly indicates that the momentum-dependent pseudogap feature in the layered Nickelate arises from the real-space charge correlation.
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turning a Nickelate fermi surface into a cupratelike one through heterostructuring
Physical Review Letters, 2009Co-Authors: P Hansmann, A Toschi, Xiaoping Yang, G Khaliullin, O K Andersen, K HeldAbstract:Using the local density approximation and its combination with dynamical mean-field theory, we show that electronic correlations induce a single-sheet, cupratelike Fermi surface for hole-doped 1=1 LaNiO3=LaAlO3 heterostructures, even though both eg orbitals contribute to it. The Ni 3d 3z 2 � 1 orbital plays the role of the axial Cu 4s-like orbital in the cuprates. These two results indicate that ‘‘orbital engineering’’ by means of heterostructuring should be possible. As we also find strong antiferromagnetic correlations, the low-energy electronic and spin excitations in Nickelate heterostructures resemble those of high-temperature cuprate superconductors. The discovery of high-temperature superconductivity (HTSC) in hole-doped cuprates [1] initiated the quest for finding related transition-metal oxides with comparable or even higher transition temperatures. In some systems, such as ruthenates [2] and cobaltates [3], superconductivity has been found. However, in these t2g systems superconductivity is very different from that in cuprates, and transition temperatures (Tc’s) are considerably lower. As it became possible to grow transition-metal oxides in heterostructures, this quest got a new direction: Novel effectively two-dimensional (2D) systems could be engineered. But which oxides, besides cuprates, are most promising for getting high Tc’s? The basic band structure of the hole-doped cuprates is that of a single 2D Cu 3d x 2 � y 2-like band which is less than half filled (configuration d 9� h ). In this situation, antiferromagnetic fluctuations prevail and are often believed to mediate the superconductivity. The Fermi surface (FS) from this x 2 � y 2 band has been observed in many overdoped cuprates and found to agree with the predictions of local density-functional (LDA) band theory. Recently the following idea for arriving at a cupratelike situation in Nickelates was presented [4]: Bulk LaNiO3 (d 7 ) has one electron in two degenerate eg bands, but sandwiching a LaNiO3 layer between layers of an insulating oxide such as LaAlO3 will confine the 3z 2 � 1 orbital in the z direction and may remove this band from the Fermi level, thus leaving the electron in the x 2 � y 2 band. The possibility of finding bulk Nickelates with an electronic structure analogous to that of cuprates was discarded awhile ago [5], but heterostructures offer new perspectives. Indeed, a major reconstruction of orbital states at oxide interfaces may recently have been observed [6], and this kind of phenomenon could lead to novel phases not present in the bulk. Extensive theoretical studies of mechanisms for orbital selection in correlated systems [7] have revealed the complexity of this problem, where details of the electronic structure and lattice distortions play decisive roles. It is therefore crucial to examine Nickelate heterostructures by means of state-of-the-art theoretical methods and find the optimal conditions for x 2 � y 2 orbital selection. In this Letter we present results of electronic-structure calculations using the merger [8] of LDA band theory, which provides an ab initio description of the materials chemistry, and the dynamical mean-field theory (DMFT) [9], which includes electronic correlations. We find that the hopping between the x 2 � y 2 and 3z 2 � 1 orbitals substantially reduces the effects of correlations in the 3z 2 � 1 orbital. In this respect, eg electrons behave very differently than the t2g electrons, which have no interorbital hopping on a square lattice. Nevertheless, we do find that the correlations may sufficiently shift the bottom of the hybridizing e g bands relatively to each other to yield a FS with only one sheet. This sheet has predominantly x 2 � y 2 character and a shape like in the cuprates with the highest Tc max (Tc at optimum hole doping) [10], but even more extreme. Moreover, stretching the in-plane lattice constants by suitable choice of substrate reduces the correlation strength needed to produce a single-sheet FS. Since we also find strong antiferromagnetic fluctuations, somewhat larger than in the cuprates, Nickelate heterostructures hold the basic ingredients for high-temperature superconductivity.
