Confinement-induced metal-to-insulator transition in strained LaNiO_{3}/LaAlO_{3} superlattices (original) (raw)

Effect of polar discontinuity on the growth of LaNiO[sub 3]/LaAlO[sub 3] superlattices

Applied Physics Letters, 2010

We have conducted a detailed microscopic investigation of [LaNiO3(1 u.c.)/LaAlO3(1 u.c.)]N superlattices grown on (001) SrTiO3 and LaAlO3 to explore the influence of polar mismatch on the resulting electronic and structural properties. Our data demonstrate that the initial growth on the non-polar SrTiO3 surface leads to a rough morphology and unusual 2+ valence of Ni in the first LaNiO3 layer, which is not observed after growth on the polar surface of LaAlO3. A newly devised model suggests that the polar mismatch can be resolved if the perovskite layers grow with an excess of LaO, which also accounts for the observed electronic, chemical, and structural effects.

Structure, strain, and the ground state of the LaTiO3/LaAlO3 superlattice

Physical Review B, 2014

Using first-principles density functional theory calculations, we examined the ground state property of LaTiO3/LaAlO3 superlattice. Total energy calculations, taking account of the structural distortions, U dependence, and exchange correlation functional dependence, show that the spin and orbital ground state can be controlled systematically by the epitaxial strain. In the wide range of strains, ferromagnetic spin and antiferro orbital ordering are stabilized, which is notably different from the previously reported ground state in titanate systems. By applying large tensile strains, the system can be transformed into an antiferromagnetic spin and ferro-orbital-ordered phase.

Orbital control in strained ultra-thin LaNiO 3 /LaAlO 3 superlattices

EPL (Europhysics Letters), 2011

In pursuit of rational control of orbital polarization, we present a combined experimental and theoretical study of single unit cell LaNiO3/LaAlO3 superlattices. Polarized x-ray absorption spectra show a distinct asymmetry in the orbital response under tensile vs. compressive strain. A splitting of orbital energies ∼100 meV with octahedral distortions is found for the case of compressive strain which is much smaller than the 3d bandwidth. In sharp contrast, for tensile strain, no splitting is found although a strong orbital polarization is still present. Density functional theory calculations of the electronic properties reveal that the asymmetry results from a combination of strain effects and altered covalency in the bonding across the interfacial apical oxygen to the Al site, leading to the opening of a pseudogap in the heterostructure for tensile strain.

Quantum confinement of Mott electrons in ultrathin LaNiO_{3}/LaAlO_{3} superlattices

Physical Review B, 2011

We investigate the electronic reconstruction in (LaNiO3)n/(LaAlO3)3 (n =3, 5 and 10) superlattices due to the quantum confinement (QC) by d.c. transport and resonant soft x-ray absorption spectroscopy. In proximity to the QC limit, a Mott-type transition from an itinerant electron behavior to a localized state is observed. The system exhibits tendency towards charge-order during the transition. ab initio cluster calculations are in good agreement with the absorption spectra, indicating that the apical ligand hole density is highly suppressed resulting in a strong modification of the electronic structure. At the dimensional crossover cellular dynamicalmean-field calculations support the emergence of a Mott insulator ground state in the heterostructured ultra-thin slab of LaNiO3.

Graded orbital occupation near interfaces in a La_{2}NiO_{4}-La_{2}CuO_{4} superlattice

Physical Review B, 2011

X-ray absorption spectroscopy and resonant soft x-ray reflectivity show a non-uniform distribution of oxygen holes in a La2NiO4 − La2CuO4 (LNO-LCO) superlattice, with excess holes concentrated in the LNO layers. Weak ferromagnetism with Tc = 160 K suggests a coordinated tilting of NiO6 octahedra, similar to that of bulk LNO. Ni d 3z 2 −r 2 orbitals within the LNO layers have a spatially variable occupation. This variation of the Ni valence near LNO-LCO interfaces is observed with resonant soft x-ray reflectivity at the Ni L edge, at a reflection suppressed by the symmetry of the structure, and is possible through graded doping with holes, due to oxygen interstitials taken up preferentially by inner LNO layers. Since the density of oxygen atoms in the structure can be smoothly varied with standard procedures, this orbital occupation, robust up to at least 280 K, is tunable.

Effect of polar discontinuity on the growth of LaNiO3/LaAlO3 superlattices

Applied Physics Letters, 2010

We have conducted a detailed microscopic investigation of [LaNiO3(1 u.c.)/LaAlO3(1 u.c.)]N superlattices grown on (001) SrTiO3 and LaAlO3 to explore the influence of polar mismatch on the resulting electronic and structural properties. Our data demonstrate that the initial growth on the nonpolar SrTiO3 surface leads to a rough morphology and unusual 2+ valence of Ni in the initial LaNiO3 layer, which is not observed after growth on the polar surface of LaAlO3. A devised model suggests that the polar mismatch can be resolved if the perovskite layers grow with an excess of LaO, which also accounts for the observed electronic, chemical, and structural effects.

Charge transfer, confinement, and ferromagnetism in LaMnO3/LaNiO3(001) superlattices

Physical Review B, 2013

Using first-principles density functional theory calculations, we investigated the electronic structure and magnetic properties of (LaMnO3)m/(LaNiO3)n superlattices stacked along (001)-direction. The electrons are transferred from Mn to Ni, and the magnetic moments are induced at Ni sites that are paramagnetic in bulk and other types of superlattices. The size of induced moment is linearly proportional to the amount of transferred electrons, but it is larger than the net charge transfer because the spin and orbital directions play important roles and complicate the transfer process. The charge transfer and magnetic properties of the (m,n) superlattice can be controlled by changing the m/n ratio. Considering the ferromagnetic couplings between Mn and Ni spins and the charge transfer characteristic, we propose the (2,1) superlattice as the largest moment superlattice carrying ∼8µB per formula unit.