Abstract
Nickelates are a rich class of materials, ranging from insulating magnets to superconductors. But for stoichiometric materials, insulating behavior is the norm, as for most late transition metal oxides. Notable exceptions are the 3D perovskite LaNiO3, an unconventional paramagnetic metal, and the layered Ruddlesden-Popper phases R4Ni3O10, (R = La, Pr, Nd). The latter are particularly intriguing because they exhibit an unusual metal-to-metal transition. Here, we demonstrate that this transition results from an incommensurate density wave with both charge and magnetic character that lies closer in its behavior to the metallic density wave seen in chromium metal than the insulating stripes typically found in single-layer nickelates like La2-xSrxNiO4. We identify these intertwined density waves as being Fermi surface-driven, revealing a novel ordering mechanism in this nickelate that reflects a coupling among charge, spin, and lattice degrees of freedom that differs not only from the single-layer materials, but from the 3D perovskites as well.
Highlights
4, Hong Zheng[1], M
As a case in point, the family of rare earth nickel oxide perovskites, RNiO3 (R = La, Pr–Lu), presents an important archetype transition metal oxides (TMO) for investigating the nexus between charge localization and itineracy and their correlation with magnetism. These well-studied Ni3+ (d7) perovskites exhibit a commensurate antiferromagnetic insulating ground state for all R except La, and the ordering wavevectors driving the metal-insulator transition (MIT) and magnetic ordering are commensurate with respect to the parent cubic perovskite[1]
Long-range ordered antiferromagnetism in bulk samples[2,3,4,5], evidence of short-range bond disproportionation associated with qMIT has been reported[6]
Summary
Prominent peaks at l = 2 and 6 along the (0, 0.62, l) cut (Fig. 3c) indicate an approximate pattern of l = 4n + 2 when h = 0 This selection rule implies that the magnetic stacking pattern of the six planes in the unit cell (three per trilayer) is "; À; #;"; À; #, where – represents a node. La4Ni3O10 are quite strong, and there is no evidence (Fig. 1d, e) that the CDW amplitude is secondary in the sense of the Landau theory of phase transitions (i.e., quadratic in the SDW amplitude) In this regard, La4Ni3O10 echoes its reduced analog, La4Ni3O8, though in that case one finds a semiconductor to insulator transition and a real space charge-stripe and spin-stripe scenario with a commensurate wavevector[9,10]. This behavior contrasts with chromium, where the CDW/strain wave is clearly a secondary order parameter[29]
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