Phase diagram of infinite layer nickel superconductor

The figure (above) shows the conversion of the perovskite structure Nd1-xSrxNiO3 to the infinite layer structure Nd1-xSrxNiO2 using calcium hydride (CaH2). The figure (bottom) shows a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image and a phase diagram of the infinite layer Nd1-xSrxNiO2 film on a single crystal SrTiO3 substrate. Tc90% R and Tc10% R are defined as the temperatures at which the resistivity drops to 90% and 10% of the value at 15 K (start of superconductivity), respectively. The inset in the upper left corner of the plot is an enlarged view of the superconducting dome area. TH indicates the temperature at which most of the charge carriers change from electrons to holes. Credits: Physical Review Letters

NUS physicists have developed a method for transitioning rare earth nickel salts from their original perovskite form to an infinite layer structure. This allowed them to create a complete phase diagram of this nickelate superconductor.

A superconductor is a material system that allows a current to flow with zero resistance when it falls below the “critical temperature” known as the superconducting transition temperature T.c..Traditional superconductors usually have a Tc It is lower than the limit of about 30 K (268 degrees below room temperature) predicted based on the Bardeen–Cooper–Schrieffer (BCS) theory. This limits the use of superconducting devices in our daily lives.For decades, researchers have been trying to push this Tc It will be higher by synthesizing new materials. Understanding the physical mechanism is also important. The so-called high-temperature superconductivity of compounds containing a copper oxide layer (known as copper oxide), Tc It was discovered in the late 1980s that the limits of BCS were exceeded, followed by the boiling point of liquid nitrogen (77 K). Since then, Tc It is stagnant and has produced important research results, but the origin and mechanism of high TcSuperconductivity is still a mystery. A new superconducting family with crystal and electronic structures similar to copper oxide is one way to look for potentially high T.c Understand the underlying mechanism of materials and high Tc Superconductivity.

Recently, researchers have discovered that superconductivity exists in rare earth nickelate compounds, which are analogs of cuprate oxides. By studying this copper oxide analog, we may be able to better understand high-temperature superconductivity and predict, design, and synthesize higher T.c Superconductor. However, it has become clear that nickelate superconductors are more difficult to manufacture than originally thought. Nine months after this discovery, a research team led by Professor ARIANDO of the NUS Faculty of Physics became the first group to reproduce this result. More importantly, they have succeeded in developing a phase diagram of nickelate superconductors.

To achieve this, Professor ARIANDO’s group has developed a topotactic reduction technique for converting thin films of rare earth nickel salts (NdNiO).2) From the usual perovskite crystal form to a new doped structure known as the infinite layer structure. In this material, doping a nickelate compound with a strontium (Sr) impurity causes superconductivity and exists in an infinite layer structure. This technology allowed the research team to study superconductivity as a function of doping. They created a phase diagram of this material system and discovered the existence of a superconducting dome region (doping-dependent T).c) And weak insulation on the sides of the dome (see figure).

In their experiments, researchers used pulsed laser deposition technology to synthesize Sr-doped nickelate Nd.1-xSeniorXNiO3 Thin film on strontium titanate (SrTiO)3)substrate. As-grown thin film and reagent calcium hydride (CaH)2), Placed in a vacuum chamber to induce a reduction reaction.NiO apical oxygen atom during reduction process6 The octahedron is deleted.This will generate perovskite Nd1-xSeniorXNiO3 Convert to infinite layer Nd1-xSeniorXNiO2.. Researchers have applied different levels of Sr doping levels and found that superconductivity appears in the infinite layer of Nd.1-xSeniorXNiO2 When the Sr composition is between x = 0.135 and 0.235. This creates a superconducting dome-shaped region. More interestingly, they found that in addition to the superconducting region, weak insulation behavior was observed at low temperatures.This unique behavior is different from other high Tc Material systems such as copper oxide.

“By introducing the appropriate impurities into the insulating parent compound, the nickel salt material system can exhibit high T,” said Professor Ariando.c Superconductivity. Our findings can better understand the doping-dependent properties of these material systems and provide further insights for searching for other superconducting materials in the “nickel family”. ”

Modified nickelate materials may improve understanding of high temperature superconductivity

For more information:
Shengwei Zeng et al. Phase diagram of infinite layer Nd1-xSrxNiO2 thin film and superconducting dome, Physical review letter (2020). DOI: 10.1103 / PhysRevLett.125.147003

Courtesy of National University of Singapore

Quote: Https: // infinite layer nickel superconductor obtained on January 18, 2021 (January 18, 2021) ) State diagram

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Phase diagram of infinite layer nickel superconductor

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