Electronic structure and magnetic tendencies of trilayer La₄Ni₃O₁₀ under pressure: Structural transition, molecular orbitals, and layer differentiation

Summary

Motivated by the recent observation of superconductivity in the pressurized trilayer Ruddlesden-Popper (RP) nickelate La₄⁢Ni₃⁢O₁₀, we explore its structural, electronic, and magnetic properties as a function of hydrostatic pressure from first-principles calculations. We find that an orthorhombic (monoclinic)-to-tetragonal transition under pressure takes place concomitantly with the onset of superconductivity. The electronic structure of La₄⁢Ni₃⁢O₁₀ can be understood using a molecular trimer basis wherein 𝑛 molecular subbands arise as the 𝑑𝑧2 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 ↑, 0, ↓ stacking that is consistent with the spin density wave model previously suggested by neutron diffraction. Such a state is destabilized at the pressure where superconductivity arises. Despite the presence of 𝑑𝑧2 states at the Fermi level, the 𝑑𝑥2−𝑦2 orbitals also play a key role in the electronic structure of La₄⁢Ni₃⁢O₁₀. This active role of the 𝑑𝑥2−𝑦2 states in the low-energy physics of the trilayer RP nickelate, together with the distinct electronic behavior of the inner and outer planes, resembles the physics of multilayer cuprates.

Materials

• La₄Ni₃O₁₀

Methods

• first-principles calculations

Keywords

• structural transition
• molecular trimer basis
• layer differentiation
• spin density wave
• antiferromagnetic coupling

Highlights

• The dx2-y2 orbitals play a key role in the electronic structure, resembling the physics of multilayer cuprates.

Conclusions

• An orthorhombic (monoclinic)-to-tetragonal transition under pressure takes place concomitantly with the onset of superconductivity.
• The electronic structure can be understood using a molecular trimer basis wherein n molecular subbands arise as the dz2 orbitals hybridize strongly along the c axis.
• 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 (↑,0,↓ stacking).

Main claims

• The ambient-pressure ground state of La₄Ni₃O₁₀ consists of nonmagnetic inner NiO₂ layers and stripe-ordered outer layers with antiferromagnetic coupling along c, consistent with the SDW model suggested by neutron diffraction.
  • Evidence: GGA+U calculations show M/0/M state with magnetic moments on outer layers and nearly zero on inner layer; out-of-plane coupling is ↑,0,↓.
• This magnetic state is destabilized at the pressure where superconductivity arises (around 30 GPa), where a ferromagnetic state with moments on all layers becomes competitive.
  • Evidence: Energy differences at 30 GPa favor FM state for Hubbard U>4 eV; M/0/M state is no longer lowest.
• The electronic structure can be understood via a molecular trimer picture where dz2 orbitals form bonding, nonbonding, and antibonding states, with active dx2-y2 orbitals resembling multilayer cuprates.
  • Evidence: Band structure shows clear molecular orbital splittings; both eg orbitals are active near Fermi level.

Workflow

• Structural Relaxation and Phonon Calculations — A structural transition to tetragonal I₄/mmm phase occurs under pressure, concomitant with superconductivity onset.
  • Materials: La₄Ni₃O₁₀
  • Methods: DFT (VASP) with GGA-PBE; frozen-phonon method (Phonopy)
  • Observations: Orthorhombic (monoclinic)-to-tetragonal transition near 10-15 GPa; unstable X₂+ and X₃+ modes quenched with pressure
• Electronic Structure Analysis (Molecular Orbital Picture) — Electronic structure can be understood using a molecular trimer basis, with n molecular subbands for dz2.
  • Materials: La₄Ni₃O₁₀
  • Methods: DFT (WIEN₂K) with GGA-PBE; site- and orbital-resolved band structure
  • Observations: dz2 orbitals form bonding-nonbonding-antibonding molecular orbitals; dx2-y2 orbitals active; γ pocket appears at high pressure
• Magnetic Calculations (GGA+U) — Ground state at ambient pressure has nonmagnetic inner planes and stripe-ordered outer planes antiferromagnetically coupled along c (↑,0,↓), consistent with neutron diffraction.
  • Materials: La₄Ni₃O₁₀
  • Methods: GGA+U with AMF double-counting; U range 2-5 eV, JH=0.7 eV
  • Observations: At ambient pressure, M/0/M state with stripe-ordered outer layers (π,0) and nonmagnetic inner layer is ground state; at 30 GPa, FM state is favored for U>4 eV