Stacked charge stripes in the quasi-2D trilayer nickelate La ₄ Ni ₃ O ₈

Abstract

The quasi-2D nickelate La 4 Ni 3 O 8 (La-438), consisting of trilayer networks of square planar Ni ions, is a member of the so-called T′ family, which is derived from the Ruddlesden-Popper (R-P) parent compound La 4 Ni 3 O 10−x by removing two oxygen atoms and rearranging the rock salt layers to fluorite-type layers. Although 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-pO 2 floating zone-grown single crystals that this transition is associated with 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 R-P nickelate, La 5/3 Sr 1/3 NiO 4 (LSNO-1/3; Ni 2.33+ ), with orientation at 45°to the Ni-O bonds. The charge stripes in La-438 are weakly correlated along c to form a staggered ABAB stacking that reduces 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.charge stripe | charge order | nickelate | strongly correlated materials | transition metal oxides C ompetition between localized and itinerant electron behavior is an organizing construct in our understanding of correlated electron transition metal oxide (TMO) physics (1-4). Some of the most compelling phenomenology in these materials occurs in the mixed valent state for the transition metal, which is set by composition, doping, and anion coordination of the metal. Many mixed valent TMOs adopt insulating "charge ordered" states, in which an inhomogeneous but long-range ordered configuration of the charge density condenses from a uniform metallic state (5). The real space pattern of charge order varies by material (6-9), but a typically observed motif is some variety of charge stripes. Such stripes have been observed in cobaltites (10-12), cuprates (13-15), nickelates (16)(17)(18)(19), and manganites (20-22), albeit with highly materials-dependent configurations that hinge on a balance among Coulomb, lattice, and magnetic exchange energies. For instance, charge stripes in layered nickelates typically stagger themselves from layer to layer to reduce the collective electrostatic energy arising from the charge disproportionation (9, 18).Indeed, the case of nickelates plays a prominent role in charge stripe physics (6-9, 16-19, 23-28), because mixed valent Ni 2+ (d 8 ) and Ni 3+ (d 7 ) compounds, such as La 2 − x Sr x NiO 4 (LSNO), are structurally and electronically related to high T c superconductors and thus, have been targeted as potential alternatives to the cuprates. Instead of superconductivity, however, the ground state of such quasi-2D, octahedrally coordinated nickelates is marked by stati...

Fermiology and electron dynamics of trilayer nickelate La4Ni3O10

“…However, such studies have not been possible until now because of the difficulty of preparing high-quality single crystal samples. This has recently been overcome for trilayer nickelates through the use of special high-pressure floating-zone image furnaces, which now enable single crystals of these nickelates to be prepared 10 . In the planar-trilayer nickelate La 4 Ni 3 O 8 , recent studies 10, 12 have revealed stripe charge ordering with a phase transition at 105 K. As for La 4 Ni 3 O 10 , a charge–density wave instability has been predicted below the metal-to-metal transition around 140 K 13, 14 .…”

Magnetic order-disorder transitions on a one-third-depleted square lattice

“…The one third depleted geometry that we investigated has recently been shown to be realized as a result of charge stripe ordering in the nickelates 23,24 , so our simulations speak to the conditions for AF order in those materials. The relative strengths of first and second neighbor exchange couplings for nickelates has not yet been addressed.…”

“…1, which more directly connects with the notion of 'depletion' and which also fundamentally involves magnetic order, is provided by recent experimental 23 29 .…”

“…The relative strengths of first and second neighbor exchange couplings for nickelates has not yet been addressed. Another key feature is the presence of multiple NiO 2 layers and the surprising nature of charge equivalence between the layers 23,24 . We cannot immediately address this phenomenon, since in our treatment charge ordering is put in a priori through our consideration of a one third depleted lattice and, in addition, our restriction to a single layer model.…”

Charge-stripe order, antiferromagnetism, and spin dynamics in the cuprate-analog nickelate La4Ni3O8

“…The crystal structure of this compound involves square planar NiO 2 trilayers, isoelectronic to the Cu 2+ O 2 layers of the cuprates if the Ni valence were 1+. Further interest in comparing these systems arises from an antiferromagnetic (AFM) phase transition in La 4 Ni 3 O 8 at a Néel temperature T N = 105 K into a state with commensurate spin and charge stripes [4][5][6], similar in some respects to the AFM transition occurring * Present address: Lawrence Livermore National Laboratory, Livermore, California 94550, USA.…”