Stacked Charge Stripes in Quasi-Two_Dimensional Trilayer Nickelate La4Ni3O8

TL;DR

This study reveals that La4Ni3O8 exhibits a charge stripe order at 105 K, with a unique in-phase stacking within trilayers, advancing understanding of charge ordering in layered nickelates.

Contribution

It demonstrates the existence of a quasi-2D charge stripe ground state in La4Ni3O8 and details its stacking pattern, which differs from expectations based on Coulomb interactions.

Findings

Charge stripe order appears at 105 K.

Charge stripes are weakly correlated along the c axis.

Within trilayers, charge stripes are stacked in phase.

Abstract

The quasi-two-dimensional nickelate La4Ni3O8 (La-438) is an anion deficient n=3 Ruddlesden-Popper (R-P) phase that consists of trilayer networks of square planar Ni ions, formally assigned as Ni1+ and Ni2+ in a 2:1 ratio. While previous studies on polycrystalline samples have identified a 105 K phase transition with a pronounced electronic and magnetic response but weak lattice character, no consensus on the origin of this transition has been reached. Here we show using synchrotron x-ray diffraction on high-pO2 floating-zone grown single crystals that this transition is driven by a real space ordering of charge into a quasi-2D charge stripe ground state. The charge stripe superlattice propagation vector, q=(2/3, 0, 1), corresponds with that found in the related 1/3-hole doped single layer Ruddlesden-Popper nickelate, La5/3Sr1/3NiO4 (LSNO-1/3, Ni2.33+) with orientation at 45-degrees to the Ni-O bonds. Like LSNO-1/3, the charge stripes in La-438 are weakly correlated along the c axis to form a staggered ABAB stacking that minimizes the Coulomb repulsion among the stripes. Surprisingly, however, we find that the charge stripes within each trilayer of La-438 are stacked in phase from one layer to the next, at odds with any simple Coulomb repulsion argument.