at ambient pressure*

The recent discovery of an 80~K superconducting state stabilized under pressure in La₃Ni₂O₇ [1] has provided an exciting new opportunity to study and develop high-temperature unconventional superconductors beyond the cuprates. One of the most striking observations of this material is that superconductivity is linked to a subtle change in the space group of the material that occurs under pressure. This raises important questions about how the structure and superconducting state are interconnected and whether it is possible to stabilize the superconducting state at ambient pressure.

 

Using Density functional theory-based structural relaxations, we have explored how the crystal structure of La₃Ni₂O₇ responds to external tuning parameters, such as uniaxial and biaxial strain [2]. Our study reveals two key results. Firstly, the structural transition is captured entirely within the mean-field framework of DFT, without the need for any correlated parameter such as a Hubbard U. And secondly, the structural transition observed under pressure is mediated almost entirely by a reduction of the b-axis lattice constant, which suggests that uniaxial compression along the [010] direction or in-plane biaxial compression are also sufficient as tuning parameters to control this structural transition.

Furthermore, we show that increasing the size of the A-site cations can also induce the structural transition via chemical pressure, and identify Ac₃Ni₂O₇ and Ba₃Ni₂O₇ as potential candidates for a high-temperature superconducting nickelate at ambient pressure.

 

[1] Sun et al. Nature, 621, 493-498 (2023)

[2] LCR and PW, arXiv:2309.15745 (2023)