Electronic structure and magnetic tendencies of trilayer La$_4$Ni$_3$O$_{10}$ under pressure: structural transition, molecular orbitals, and layer differentiation

TL;DR

This study uses first-principles calculations to analyze how pressure affects the structure, electronic states, and magnetism of trilayer La$_4$Ni$_3$O$_{10}$, revealing a structural transition linked to superconductivity and complex orbital interactions.

Contribution

It provides a detailed first-principles analysis of pressure-induced structural, electronic, and magnetic changes in trilayer La$_4$Ni$_3$O$_{10}$, highlighting the role of molecular orbitals and layer differentiation.

Findings

Orthorhombic-to-tetragonal transition under pressure coincides with superconductivity onset.

Electronic structure involves molecular $d_{z^2}$ orbitals hybridized along the c-axis.

Magnetic ground state features nonmagnetic inner and stripe-ordered outer planes.

Abstract

Motivated by the recent observation of superconductivity in the pressurized trilayer La$_4$Ni$_3$O$_{10}$ Ruddlesden-Popper (RP) nickelate, we explore its structural, electronic, and magnetic properties as a function of hydrostatic pressure from first-principles calculations. We find that in both the bilayer and trilayer nickelates, an orthorhombic(monoclinic)-to-tetragonal transition under pressure takes place concomitantly with the onset of superconductivity. The electronic structure of La$_4$Ni$_3$O$_{10}$ can be understood using a molecular trimer basis wherein $n$ molecular subbands arise as the $d_{z^2}$ orbitals hybridize strongly along the $c$-axis within the trilayer. The magnetic tendencies indicate that the ground state at ambient pressure is formed by nonmagnetic inner planes and stripe-ordered outer planes that are antiferromagnetically coupled along the $c$ axis, resulting in an unusual $\uparrow$, 0, $\downarrow$ stacking that is consistent with the spin density wave model suggested by neutron diffraction. Such a state is destabilized by the pressures wherein superconductivity arises. Despite the presence of $d_{z^2}$ states at the Fermi level, the $d_{x^2-y^2}$ orbitals also play a key role in the electronic structure of La$_4$Ni$_3$O$_{10}$. This active role of the $d_{x^2-y^2}$ states in the low-energy physics of the trilayer RP nickelate, together with the distinct electronic behavior of inner and outer planes, resembles the physics of multilayer cuprates.