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![| Schematic unified electronic phase diagram of d 9 nickelates and cuprates as a function of d electron count. Inspired by Refs. [3, 4] and [38].](publication/357283870/figure/fig2/AS:1104226600132611@1640279545782/Schematic-unified-electronic-phase-diagram-of-d-9-nickelates-and-cuprates-as-a-function.png)
| Schematic unified electronic phase diagram of d 9 nickelates and cuprates as a function of d electron count. Inspired by Refs. [3, 4] and [38].
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The 2019 discovery of high temperature superconductivity in layered nickelate films, Nd 1-x SrNiO 2 , has galvanized a community that has been studying nickelates for more than 30 years both as cuprate analogs and in their own right. On the surface, infinite layer nickelates, and their multilayer analogs, should be promising candidates based on our...
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Context 1
... in infinite layer (Nd,Sr)NiO 2 and the putative trilayer (Pr,Ce) 4 Ni 3 O 8 the doping is provided by aliovalent substitution on the A site, it is also possible to self-dope the higher order members of the R n+1 Ni n O 2n+2 series, as the formal Ni oxidation state follows (n+1)/n. Thus, by stacking more layers, the average Ni oxidation state will progressively move into the superconducting dome of the cuprates and the infinite-layer nickelates, entering perhaps at n 4 and certainly by n 5 (See Figure 2). This hypothesis proved to be correct, as shown in Figure 1B (middle). ...
Similar publications
The 2019 discovery of high temperature superconductivity in layered nickelate films, Nd$_{1-x}$SrNiO$_2$, has galvanized a community that has been studying nickelates for more than 30 years both as cuprate analogs and in their own right. On the surface, infinite layer nickelates, and their multilayer analogs, should be promising candidates based on...
Citations
... [17][18][19][20][21][22][23] The infinite-layer nickelate RNiO 2 (R = rare-earth elements) possesses an identical crystal structure to the cuprate parent compound CaCuO 2 . Besides, although there exist several differences between the two transition metal ions, 24 the electronic configuration of Ni + in layered nickelates resembles those of Cu 2+ in cuprates, 25,26 with a nominal d 9 configuration, where their antibonding e g shells are partially filled with three electrons, with a single hole in the 3d x 2 Ày 2 orbital. ...
Since superconductivity was first reported in nickelate thin films, many studies have been published about this family of materials, and different hypotheses have been proposed for explaining the mechanisms and structural dependence. Here, we report the synthesis of anchored infinite-layer LaNi0.9Al0.1O2.1 and its hole-doped derivatives by topotactic reduction from La1-xSrxNi0.9Al0.1O3 rhombohedral perovskites. LaNiO2 derivatives constitute a new family of high-temperature superconductors, with the same structure as high-Tc cuprates but based on nickel, only showing superconductivity in thin films for now. We describe a strategy to stabilize LaNiO2 derivatives in bulk: the presence of Al at the octahedral sites helps to stabilize/anchor the infinite layer structure. The reasons for the bulk being non-superconductors are hotly debated in the literature. An important question is whether there is some hydrogen incorporated into the structure during the reduction process from LaNiO3 to LaNiO2, predicted theoretically but not reported experimentally. Our neutron powder diffraction data show that, indeed, hydrogen occupies the centers of the Ni-O squares, and spectroscopic evidence from EELS and XAS suggests that Ni is reduced to the Ni+ oxidation state, consistent with the crystallochemical data.
... Since 2019, the field has been reinvigorated 30 by the discovery of superconducting behavior in hole-doped rare-earth nickelates with an infinite-layer crystal structure. [31][32][33][34][35][36] This structure can be achieved through the topotactic oxygen deintercalation of the perovskite phase. ...
The recent discovery of superconductivity in hole-doped infinite-layer nickelates has triggered a great interest in the synthesis of novel nickelate phases, which have primarily been examined in thin film samples. Here, we report the high-pressure optical floating zone growth of various perovskite and perovskite-derived rare-earth nickelate single-crystals and investigate the effects of hole-, electron-, and self-doping. For hole-doping with Ca and Sr, we observe phase separations during the growth process when a substitution level of 8% is exceeded. A similar trend emerges for electron-doping with Ce and Zr. Employing lower doping levels allows us to grow sizable crystals in the perovskite phase, which exhibit significantly different electronic and magnetic properties than the undoped parent compounds, such as decreased resistivity and a suppressed magnetic response. Our insights into the doping-dependent phase formation and the resulting properties of the synthesized crystals reveal limitations and opportunities for the exploration and manipulation of electronic states in rare-earth nickelates.
... The recently discovered superconductivity in holedoped infinite-layer nickelate Nd1− Sr NiO2 films, as an analogue of cuprates, has attracted much research attention, providing new opportunities to investigate the underlying physics of highc superconductivity (HTSC). [1][2][3][4][5][6][7][8][9][10][11] Due to the instability of +1 valence state of nickel, the infinite-layer nickelate is hard to grow directly. Instead, the precursor phase, perovskite nickelate (Nd,Sr)NiO3, is synthesized first and soft-chemically reduced subsequently to the infinite-layer phase (Nd,Sr)NiO2 with reductive agents, such as sodium hydride. ...
The nickel-based superconductivity provides a fascinating new platform to explore high- T c superconductivity. As the infinite-layer nickelates are obtained by removing the apical oxygens from the precursor perovskite phase, the crystalline quality of the perovskite phase is crucial in synthesizing high quality superconducting nickelates. Especially, cation-related defects, such as the Ruddlesden–Popper-type (RP-type) faults, are unlikely to disappear after the topotactic reduction process and should be avoided during the growth of the perovskite phase. Herein, using reactive molecular beam epitaxy, we report the atomic-scale engineering of the interface structure and demonstrate its impact in reducing crystalline defects in Nd-based nickelate/SrTiO 3 heterostructures. A simultaneous deposition of stoichiometric Nd and Ni directly on SrTiO 3 substrates results in prominent Nd vacancies and Ti diffusion at the interface and RP-type defects in nickelate films. In contrast, inserting an extra [NdO] monolayer before the simultaneous deposition of Nd and Ni forms a sharp interface and greatly eliminates RP-type defects in nickelate films. A possible explanation related to the polar discontinuity is also discussed. Our results provide an effective method to synthesize high-quality precursor perovskite phase for the investigation of the novel superconductivity in nickelates.
... The discovery of superconductivity in the thin film of Nd0.8Sr0.2NiO2 by Li et al. [1] has attracted intense attention in the fields of condensed matter physics and materials science and launched the Nickel Age of Superconductivity [2][3][4][5][6][7][8][9][10][11][12][13][14]. Until today, superconductivity with a critical temperature (Tc) in the range of 9-15 K has been observed in the infinite-layer R1-xMxNiO2 (R = La, M = Ca, Sr; R = Pr, Nd, M = Sr) [15][16][17][18][19] and the quintuplelayer Nd6Ni5O12 [20]. ...
... films [21]. After 3 years of intense research, several fundamental issues still exist [2][3][4][5][6][7][8][9][10][11][12][13][14], including the mechanism of superconductivity, the similarity and difference between nickelate and cuprate superconductivity, whether the ground state is magnetic, and whether competing phases such as pseudogaps and strange metals exist. Single crystals are the ideal platform to solve the abovementioned open questions. ...
Single crystals of the perovskite nickelate NdNiO3 with dimensions of up to 50 μm on edge have been successfully grown using the flux method at a temperature of 400 °C and oxygen pressure of 200 bar. The crystals were investigated by a combination of techniques, including high-resolution synchrotron X-ray single-crystal and powder diffraction and physical property measurements such as magnetic susceptibility and resistivity. Resistivity measurements revealed a metal-insulator transition (MIT) at TMIT~180 K with apparent thermal hysteresis; however, no superlattice peaks or peak splitting below TMIT, which corresponds to a structural transition from Pbnm to P21/n, was observed. The successful growth of NdNiO3 crystals at relatively low temperatures and oxygen pressure provides an alternative approach for preparing single crystals of interesting perovskites such as RNiO3 (R = Sm-Lu) and parent phases of superconducting square planar nickelates.
Infinite layer (IL) nickelates provide a new route beyond copper oxides to address outstanding questions in the field of unconventional superconductivity. However, their synthesis poses considerable challenges, largely hindering experimental research on this new class of oxide superconductors. That synthesis is achieved in a two‐step process that yields the most thermodynamically stable perovskite phase first, then the IL phase by topotactic reduction, the quality of the starting phase playing a crucial role. Here, a reliable synthesis of superconducting IL nickelate films is reported after successive topochemical reductions of a parent perovskite phase with nearly optimal stoichiometry. Careful analysis of the transport properties of the incompletely reduced films reveals an improvement in the strange metal behavior of their normal state resistivity over subsequent topochemical reductions, offering insight into the reduction process.
Infinite-layer nickelates R1−xSrxNiO2 (R = La, Pr, Nd) are a class of superconductors with structural similarities to cuprates. Although long-range antiferromagnetic order has not been observed for these materials, magnetic effects such as antiferromagnetic spin fluctuations and spin-glass behavior have been reported. Different experiments have drawn different conclusions about whether the pairing symmetry is s or d wave. In this paper, we applied a scanning superconducting quantum interference device (SQUID) to probe the magnetic behavior of film samples of three infinite-layer nickelates (La0.85Sr0.15NiO2, Pr0.8Sr0.2NiO2, and Nd0.775Sr0.225NiO2) grown on SrTiO3 (STO), each with a nominal thickness of 20 unit cells. In all three films, we observed a ferromagnetic background. We also measured the magnetic susceptibility above the superconducting critical temperature in Pr0.8Sr0.2NiO2 and La0.85Sr0.15NiO2 and identified a non-Curie-Weiss dynamic susceptibility. Both magnetic features are likely due to NiOx nanoparticles. Additionally, we investigated superconductivity in Pr0.8Sr0.2NiO2 and Nd0.775Sr0.225NiO2, which exhibited inhomogeneous diamagnetic screening. The superfluid density inferred from the diamagnetic susceptibility in relatively homogeneous regions shows T-linear behavior in both samples. Finally, we observed superconducting vortices in Nd0.775Sr0.225NiO2. We determined a Pearl length of 330µm for Nd0.775Sr0.225NiO2 at 300 mK, both from the strength of the diamagnetism and from the size and shape of the vortices. These results highlight the importance of considering NiOx particles when interpreting experimental results for these films.
The superconducting nickelates were first proposed as potential analogs to the cuprate unconventional superconductors in 1999, but it took twenty years before superconductivity was successfully stabilized in epitaxial thin films. Since then, a flurry of both experimental and theoretical efforts have sought to understand the similarities and differences between the two systems and how they manifest in the macroscopic superconducting and normal-state properties. Although the nickelates and cuprates indeed share many commonalities within their respective phase diagrams, several notable differences have also emerged, especially regarding their parent compounds, electronic hybridization, and fermiology. Here, we provide a survey of the rapidly developing landscape of layered nickelate superconductors, including recent experimental progress to probe not just the superconducting but also normal state and other ordered phases stabilized in these compounds.
Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 15 is March 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
The recently discovered infinite-layer nickelates show great promise in helping to disentangle the various cooperative mechanisms responsible for high-temperature superconductivity. However, lack of antiferromagnetic order in the pristine nickelates presents a challenge for connecting the physics of the cuprates and nickelates. Here, by using a quantum many-body Green’s function-based approach to treat the electronic and magnetic structures, we unveil the presence of many two- and three-dimensional magnetic stripe instabilities that are shown to persist across the phase diagram of LaNiO2. Our analysis indicates that the magnetic properties of the infinite-layer nickelates are closer to those of the doped cuprates, which host a stripe ground state, rather than the undoped cuprates. The computed longitudinal-spin, transverse-spin, and charge spectra of LaNiO2 are found to contain an admixture of contributions from localized and itinerant carriers. Theoretically obtained dispersion of magnetic excitations (spin-flip) is found to be in good accord with the results of recent resonant inelastic X-ray scattering experiments. Our study gives insight into the origin of strong magnetic competition in the infinite-layer nickelates and their relationship with the cuprates.
