[Paper Review] Investigations of key issues on the reproducibility of high-Tc superconductivity emerging from compressed La3Ni2O7

Yazhou Zhou, Jing Guo+12 more|arXiv (Cornell University)|Nov 21, 2023

Rare-earth and actinide compounds18 citations

TL;DR

The paper investigates reproducibility issues of pressure-induced superconductivity in La3Ni2O7, showing filamentary-like superconductivity, its interfacial origin, and the role of oxygen content.

ABSTRACT

Recently, the signatures of superconductivity near 80 K have been discovered in the single crystal of La3Ni2O7 under pressure, which makes it a new candidate of the high-temperature superconductors dominated by 3d transition elements after the cuprate and iron-pnictide superconductors. However, there are several critical questions that have been perplexing the scientific community. These questions include (1) what factors contribute to the inconsistent reproducibility of the experimental results? (2) what is the fundamental nature of pressure-induced superconductivity: bulk or non-bulk (filamentary-like)? (3) where does the superconducting phase locate within the sample if it is filamentary-like? (4) is the oxygen content important for developing and stabilizing its superconductivity? In this study, we employ comprehensive high-pressure techniques to address these crucial issues. Through our modulated ac susceptibility measurements, we are the first to find that the superconductivity in this nickelate is filamentary-like. Our scanning transmission electron microscopy (STEM) investigations suggest that the filamentary-like superconductivity most likely emerges at the interface between the La3Ni2O7 and La4Ni3O10 phases. By tuning the oxygen content on the polycrystalline La3Ni2O7, we also find that the oxygen content plays vital role for developing and stabilizing its superconductivity. The upper and lower bounds of the oxygen content are 7.35 and 6.89, respectively. Our results provide not only new insights into understanding the puzzling issues in this material, but also significant information for achieving a better understanding on the superconductivity of this material.

Motivation & Objective

• Motivate the reproducibility problems reported for high-Tc superconductivity in La3Ni2O7 under pressure.
• Identify whether superconductivity is bulk or filamentary, and where it localizes in the sample.
• Examine structural and chemical factors, especially phase interfaces and oxygen content, that influence superconductivity.
• Provide guidance for stabilizing superconductivity through controlled synthesis and processing.

Proposed method

• Apply high-pressure techniques to La3Ni2O7 specimens to probe superconductivity.
• Use modulated AC susceptibility to characterize the superconducting state.
• Perform scanning transmission electron microscopy to locate potential superconducting regions.
• Tune and assess oxygen content in polycrystalline La3Ni2O7 to evaluate its effect on superconductivity.
• Identify phase interfaces, particularly between La3Ni2O7 and La4Ni3O10, as potential sites of superconductivity.
• Determine upper and lower bounds of oxygen content related to superconductivity (7.35 and 6.89).

Experimental results

Research questions

• RQ1 Is the observed superconductivity under pressure bulk or filamentary-like?
• RQ2 Where in the sample does filamentary superconductivity localize if present?
• RQ3 What factors reconcile inconsistent reproducibility across experiments?
• RQ4 How does oxygen content influence the development and stabilization of superconductivity?
• RQ5 What is the role of phase interfaces in enabling superconductivity in this material?

Key findings

• Superconductivity in compressed La3Ni2O7 is filamentary-like according to modulated AC susceptibility measurements.
• STEM suggests filamentary superconductivity most likely emerges at interfaces between La3Ni2O7 and La4Ni3O10 phases.
• Oxygen content significantly affects the development and stabilization of superconductivity.
• The explored oxygen content bounds for superconductivity are 7.35 (upper) and 6.89 (lower).
• Findings provide insight into addressing reproducibility issues and advancing understanding of superconductivity in this nickelate material.