A superconducting praseodymium nickelate with infinite layer structure (2006.13369v1)

Abstract: A variety of nickel oxide compounds have long been studied for their manifestation of various correlated electron phenomena. Recently, superconductivity was observed in nanoscale infinite layer nickelate thin films of Nd${0.8}$Sr${0.2}$NiO$2$, epitaxially stabilized on SrTiO$_3$ substrates via topotactic reduction from the perovskite precursor phase. Here we present the synthesis and properties of PrNiO$_2$ thin films on SrTiO$_3$. Upon doping in Pr${0.8}$Sr$_{0.2}$NiO$_2$, we observe superconductivity with a transition temperature of 7-12 K, and robust critical current density at 2 K of 334 kA/cm$^2$. These findings indicate that superconductivity in the infinite layer nickelates is relatively insensitive to the details of the rare earth 4$f$ configuration. Furthermore, they motivate the exploration of a broader family of compounds based on two-dimensional NiO$_2$ planes, which will enable systematic investigation of the superconducting and normal state properties and their underlying mechanisms.

• The paper details a novel synthesis method using topotactic reduction and Sr doping to create PrNiO₂ thin films on SrTiO₃ substrates.
• It employs pulsed laser deposition and controlled reduction processes to achieve the infinite-layer structure without relying on a capping layer.
• Key findings include observable superconductivity with a transition temperature of 7–12 K and a critical current density of 334 kA/cm² at 2 K.

Insights into Praseodymium Nickelate Thin Films as Superconductors

The paper outlines significant research into the synthesis and superconducting properties of praseodymium nickelate (PrNiO$_2$) thin films, contributing to the wider family of infinite-layer nickelate superconductors. This ongoing exploration is pivotal in enhancing the fundamental understanding of the varying factors governing superconductivity in nickelate and related materials, drawing specific parallels to their copper-based counterparts, the cuprates.

Methodology and Synthesis

The researchers present a detailed methodology for synthesizing PrNiO$_2$ thin films on SrTiO$_3$ substrates through the topotactic reduction process of the perovskite phase, followed by strontium doping (Pr$_{0.8}$Sr$_{0.2}$NiO$_2$). The paper relies on the use of pulsed laser deposition (PLD) technology and subsequent reduction using calcium hydride under carefully controlled conditions, ensuring the realization of the desired infinite-layer structure. The absence of a SrTiO$_3$ capping layer in the synthesis, which was achieved even for films as thick as approximately 12 nm, indicates a relatively less challenging stabilization process, attributed to the favorable lattice and structural attributes of PrNiO$_2$.

Superconducting Properties

The paper reports observable superconductivity in Pr$_{0.8}$Sr$_{0.2}$NiO$_2$ with a transition temperature (T$_c$) ranging from 7 K to 12 K, similar to the T$_c$ observed in Nd$_{0.8}$Sr$_{0.2}$NiO$_2$. A noted critical current density at 2 K of 334 kA/cm$^2$ further underscores the strength of this superconducting phase. These findings suggest that superconductivity in infinite-layer nickelates may not be critically dependent on very specific electronic configurations associated with each material's 4f electron states, challenging previous notions regarding the necessity of precise fine-tuning for achieving superconducting transitions.

Structural and Electronic Properties

Detailed structural analysis using X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) confirms the successful reduction to the infinite-layer phase, and the strain analysis suggests that all films remained epitaxially strained to the substrate. Electronic measurements reveal a metal-insulator transition for perovskite PrNiO$_3$, further demonstrating the alteration in electronic behavior upon reduction and doping.

Implications and Future Prospects

This paper contributes critical insights into the influence of rare-earth elements on superconductivity, given that Pr, unlike Nd and La, does not exhibit secondary oxidation states, which streamlines the theoretical models required for understanding these materials. The implications for further paper are immense, offering new avenues for the exploration of alternative rare-earth elements that could promote higher critical temperatures or more robust superconducting phases without intricate electron interaction tuning.

In conclusion, the paper advances understanding of superconductivity in Pr-based infinite-layer nickelates. It proposes methods that extend beyond Nd and La representatives by displaying practical synthesis routes and underscoring the material's superconducting behavior's insensitivity to rare earth variation. As an extension, the research highlights the broader potential in this domain for discovering novel superconducting materials beyond the established dispositions of their analogous cuprate systems.