An experimental study found superconductivity in bilayer phase of La₃Ni₂O₇, with the highest superconducting transition temperature (T_c) ∼ 80 K under pressure. Recently, some reports claimed that there exists a competitive monolayer-trilayer structural phase in La₃Ni₂O₇ compounds. We perform the first-principles calculations and find that bilayer phase of La₃Ni₂O₇ is energetically favorable under pressure. Although extensive studies have been done to investigate the electronic correlation and potential superconducting pairing mechanism in bilayer phase of La₃Ni₂O₇, the phonon properties and electron-phonon coupling (EPC) in the high-pressure I4/mmm phase of La₃Ni₂O₇ are not reported. Using the density functional theory (DFT) combined with Wannier interpolation technique, we study the phonon properties and EPC in bilayer phase of La₃Ni₂O₇ under 29.5 GPa. Our findings reveal that EPC is insufficient to explain the observed superconducting T_c ∼ 80 K. And the calculated Fermi surface nesting may explain the experimentally observed charge density wave (CDW) transition in bilayer phase of La₃Ni₂O₇. Our calculations substantiate that bilayer phase of La₃Ni₂O₇ is an unconventional superconductor.

一项实验研究发现 La₃Ni₂O₇ 的双层相具有超导性，在压力下最高超导转变温度 （T_c） ∼ 80 K。最近，一些报道声称 La₃Ni₂O₇ 化合物中存在竞争性的单层-三层结构相。我们进行第一性原理计算，发现 La₃Ni₂O₇ 的双层相在压力下具有良好的能量。尽管已经进行了广泛的研究来研究 La₃Ni₂O₇ 双层相中的电子相关性和潜在的超导配对机制，但 La₃Ni₂O₇ 高压 I4/mmm 相中的声子特性和电子-声子耦合 （EPC） 尚未报道。利用密度泛函理论 （DFT） 结合 Wannier 插值技术，研究了 29.5 GPa 下 La₃Ni₂O₇ 双层相的声子特性和 EPC。我们的研究结果表明，EPC 不足以解释观察到的超导 T_c∼ 80 K。计算出的费米表面嵌套可以解释实验观察到的 La₃Ni₂O₇ 双层相中的电荷密度波 （CDW） 转变。我们的计算证实了 La₃Ni₂O₇ 的双层相是一种非常规超导体。