Source zotero
Authors Not available in this batch.
arXiv / Publisher https://pubs.acs.org/doi/full/10.1021/jacs.3c13094
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Published 2024-03-08
Research paradigm Both
Sample form Unknown

Summary

Very recently, a new superconductor with Tc = 80 K has been reported in nickelate (La3Ni2O7) at around 15–40 GPa conditions (Nature, 621, 493, 2023), which is the second type of unconventional superconductor, besides cuprates, with Tc above liquid nitrogen temperature. However, the phase diagram plotted in this report was mostly based on the transport measurement under low-temperature and high-pressure conditions, and the assumed corresponding X-ray diffraction (XRD) results were carried out at room temperature. This encouraged us to carry out in situ high-pressure and low-temperature synchrotron XRD experiments to determine which phase is responsible for the high Tc state. In addition to the phase transition from the orthorhombic Amam structure to the orthorhombic Fmmm structure, a tetragonal phase with the space group of I4/mmm was discovered when the sample was compressed to around 19 GPa at 40 K where the superconductivity takes place in La3Ni2O7. The calculations based on this tetragonal structure reveal that the electronic states that approached the Fermi energy were mainly dominated by the eg orbitals (3dz2 and 3dx2–y2) of Ni atoms, which are located in the oxygen octahedral crystal field. The correlation between Tc and this structural evolution, especially Ni–O octahedra regularity and the in-plane Ni–O–Ni bonding angles, is analyzed. This work sheds new light to identify what is the most likely phase responsible for superconductivity in double-layered nickelate.

Materials

Methods

  • in situ high-pressure low-temperature synchrotron XRD
  • DFT

Keywords

  • tetragonal phase i4/mmm
  • ni eg orbitals
  • structural evolution
  • ni o octahedra regularity
  • in plane ni o ni bonding angles

Highlights

  • Correlation between Tc and Ni-O octahedra regularity and in-plane Ni-O-Ni bonding angles.

Conclusions

  • A tetragonal phase with space group I4/mmm is discovered at ≈19 GPa and 40 K where superconductivity occurs in La3Ni2O7, and the electronic states near Fermi level are dominated by Ni eg orbitals.

Main claims

Not available in this batch.

Workflow

Not available in this batch.