Electronic structure of a graphene-like artificial crystal of $NdNi{O}_3$

Abstract

Artificial complex-oxide heterostructures containing ultrathin buried layers grown along the pseudocubic [111] direction have been predicted to host a plethora of exotic quantum states arising from the graphene-like lattice geometry and the interplay between strong electronic correlations and band topology. To date, however, electronic-structural investigations of such atomic layers remain an immense challenge due to the shortcomings of conventional surface-sensitive probes, with typical information depths of a few Angstroms. Here, we use a combination of bulk-sensitive soft x-ray angle-resolved photoelectron spectroscopy (SX-ARPES), hard x-ray photoelectron spectroscopy (HAXPES) and state-of-the-art first-principles calculations to demonstrate a direct and robust method for extracting momentum-resolved and angle-integrated valence-band electronic structure of an ultrathin buckled graphene-like layer of $NdNi{O}_3$ confined between two 4-unit cell-thick layers of insulating $LaAl{O}_3$. The momentum-resolved dispersion of the buried Ni d states near the Fermi level obtained via SX-ARPES is in excellent agreement with the first-principles calculations and establishes the realization of an antiferro-orbital order in this artificial lattice. The HAXPES measurements reveal the presence of a valence-band (VB) bandgap of 265 meV. Our findings open a promising avenue for designing and investigating quantum states of matter with exotic order and topology in a few buried layers.

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Cited by in corpus (4)

• Perspective: Strongly correlated and topological states in [111] grown transition metal oxide thin films and heterostructures
• Epitaxial growth of Ruddlesden-Popper neodymium nickelates Nd${}_{n+1}$Ni${}_n$O${}_{3n+1}$ ($n$ = 1-5)
• Momentum-resolved electronic structures and strong electronic correlations in graphene-like nitride superconductors
• Electronic band structure of (111) $SrRu{O}_3$ thin film$-$an angle-resolved photoemission spectroscopy study