Nickelate Superconductivity without Rare‐Earth Magnetism: (La,Sr)NiO₂

Abstract

It has led to considerable theoretical focus on this distinction. [20,21] Across the lanthanide series, systematic studies of the infinite layer nickelates using density-functional theory (DFT)-based approaches have generally shown a smooth evolution of the electronic structure, with little qualitative dissimilarity. [22,23] While these studies treat the 4f electrons as part of the lanthanide core, others have investigated 4f-orbital hybridization explicitly to consider their potential role. [20,21] In parallel with these theoretical efforts, significant advances have been made in the understanding and optimization of thin film synthesis of the Nd/Pr based systems. [12,17] Important aspects include improving the crystallinity of the strained perovskite precursor phase, as well as the subsequent oxygen deintercalation reaction. As a result, the magnitude of the normal state resistivity for optimized samples is significantly lower than in several prior reports, [24][25][26][27] consistent with these advances in materials quality. Furthermore, a key observation is that the low-temperature normal state resistivity in Nd/Pr based infinite-layer nickelate films must be below the Mott-Ioffe-Regel limit to exhibit a superconducting transition. [13,18] Given the conceptual importance of the presence or absence of superconductivity in (La,Sr) NiO 2 , and recent materials improvements, we have revisited the synthesis of La 1−x Sr x NiO 2 thin films epitaxially stabilized on SrTiO 3 substrates and the study of its phase diagram. UponThe occurrence of unconventional superconductivity in cuprates has long motivated the search for manifestations in other layered transition metal oxides. Recently, superconductivity is found in infinite-layer nickelate (Nd,Sr) NiO 2 and (Pr,Sr)NiO 2 thin films, formed by topotactic reduction from the perovskite precursor phase. A topic of much current interest is whether rare-earth moments are essential for superconductivity in this system. In this study, it is found that with significant materials optimization, substantial portions of the La 1−x Sr x NiO 2 phase diagram can enter the regime of coherent low-temperature transport (x = 0.14 − 0.20), with subsequent superconducting transitions and a maximum onset of ≈9 K at x = 0.20. Additionally, the unexpected indication of a superconducting ground state in undoped LaNiO 2 is observed, which likely reflects the self-doped nature of the electronic structure. Combining the results of (La/Pr/Nd) 1−x Sr x NiO 2 reveals a generalized superconducting dome, characterized by systematic shifts in the unit cell volume and in the relative electron-hole populations across the lanthanides.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202104083.

Phase Diagram of Nickelate Superconductors Calculated by Dynamical Vertex Approximation

“…Hence in [33], we ruled out that the Nd 4f is relevant for superconductivity. This has been spectacularly confirmed experimentally by the discovery of superconductivity in nickelates without f electrons: Ca x La 1−x NiO 2 [69] and Sr x La 1−x NiO 2 [61] have a similar T c .…”

“…In Figure 3,we see at 30% doping, the first steps into this direction. Importantly, within the superconducting doping regime which, noteworthy, is below 24% Sr-doping for Sr x Nd 1−x NiO 2 [34,35] and 21% for Sr x La 1−x NiO 2 [61], a single 3d x 2 −y 2 Ni-orbital is sufficient for the low-energy modeling. A one-band Hubbard model description based on DMFT calculations was also concluded in [32] for the undoped parent compound.…”

Dynamical Mean Field Studies of Infinite Layer Nickelates: Physics Results and Methodological Implications

“…In this section, we give an overview of results on infinite-layer nickelates in literature and a comparison to the better understood case of the layered copper oxides. We mainly focus on theoretical results [12, 13, 15-19, 21, 23, 27, 33, 44, 61-85] but present some comparison to experiments [4,10,[86][87][88][89][90][91][92][93][94][95][96][97][98], when the relevant experimental results are available. We also mention that while we are aware of the important works on the study of interface effects [63,65,69], due to space limitation, we concentrate on the study of bulk nickelates here.…”

Low Valence Nickelates: Launching the Nickel Age of Superconductivity

“…After much synthesis and characterization of low-valence layered nickelates over three decades [1][2][3][4][5][6][7], superconductivity was finally observed [8] in hole-doped RNiO 2 (initially for rare earth R Nd, later for R La [9,10] and Pr [11]) with T c exhibiting a dome-like dependence [12,13] being maximal (10-15 K) near 20% doping. This series of discoveries in RNiO 2 materials marked the beginning of a new, nickel age of superconductivity [14,15] launching a plethora of experimental [16][17][18][19][20][21][22] and theoretical work.…”