Kavli Affiliate: Gang Su
| First 5 Authors: Xin-Wei Yi, Ying Meng, Jia-Wen Li, Zheng-Wei Liao, Jing-Yang You
| Summary:
La$_{3}$Ni$_{2}$O$_{7}$ has garnered widespread interest recently due to its
high-temperature superconductivity under pressure, accompanied by charge
density wave (CDW) ordering and metal-insulator (MI) transitions in the phase
diagram. Here, we reveal with comprehensive calculations that
La$_{3}$Ni$_{2}$O$_{7}$ possesses an antiferromagnetic ground state under both
low and high pressures, with the strong Fermi surface nesting contributed by
the flat band that leads to phonon softening and electronic instabilities.
Several stable CDW orders with oxygen octahedral distortions are identified,
which can trigger the MI transitions. The estimated CDW transition temperature
($approx$120 K) at ambient pressure agrees nicely with experimental results.
In the presence of apical oxygen vacancies, we identify two different phases,
say, half distortion and full distortion phases, respectively, and their
competition can lead to a pressure-induced MI transition, in good agreement
with experimental observations. In addition, we find that the electron-phonon
coupling is too small to contribute to superconductivity. These results appear
to indicate an unconventional superconducting pairing mechanism mediated by
antiferromagnetic fluctuations. A phase diagram that is consistent with the
experimental results is given. The present results not only explain the origins
of experimentally observed CDW and MI transitions, but also provide insight for
deeply understanding the properties like superconductivity, CDW and the role of
oxygen vacancies in pressurized La$_{3}$Ni$_{2}$O$_{7}$.
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