Quantum confinement of Mott electrons in ultrathin LaNiO_{3}/LaAlO_{3} superlattices (original) (raw)
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Confinement-induced metal-to-insulator transition in strained LaNiO_{3}/LaAlO_{3} superlattices
Physical Review B, 2011
Using density functional theory calculations including a Hubbard U term we explore the effect of strain and confinement on the electronic ground state of superlattices containing the band insulator LaAlO3 and the correlated metal LaNiO3. Besides a suppression of holes at the apical oxygen, a central feature is the asymmetric response to strain in single unit cell superlattices: For tensile strain a band gap opens due to charge disproportionation at the Ni sites with two distinct magnetic moments of 1.45µB and 0.71µB. Under compressive stain, charge disproportionation is nearly quenched and the band gap collapses due to overlap of d 3z 2 −r 2 bands through a semimetallic state. This asymmetry in the electronic behavior is associated with the difference in octahedral distortions and rotations under tensile and compressive strain. The ligand hole density and the metallic state are quickly restored with increasing thickness of the (LaAlO3)n/(LaNiO3)n superlattice from n = 1 to n = 3.
Dimensionality control in the LaNiO 3 (LNO) heterostructure has attracted attention due to its two-dimensional (2D) electronic structure was predicted to have an orbital ordered insulating ground state, analogous to that of the parent compound of high-T c cuprate superconductors [P. Hansmann et al., Phys. Rev. Lett. 103, 016401 (2009)]. Here, we directly measured the electronic structure of LNO ultrathin films using in situ angle-resolved photoemission spectroscopy (ARPES). We recognized the dimensional crossover of the electronic structure around 3-unit cells (UC)-thick LNO film and observed the orbital reconstruction. However, complete orbital ordering was not achieved. Instead, we observed that the Fermi surface nesting effect became strong in the 2D LNO ultrathin film. These results indicated that the orbital reconstruction should be described by taking into account the strong nesting effect to search for the novel phenomena, such as superconductivity in 2D LNO heterostructure. In addition, the APRES spectra showed that the Fermi surface existed down to a 1-UC-thick film, which showed insulating behavior in transport measurements. We suggested that the metal-insulator transition in the transport properties may originate from Anderson localization.
Evolution of the metallic state in LaNiO3/LaAlO3 superlattices measured by Li8β -detected NMR
Physical Review B
Using ion-implanted 8 Li β-detected NMR, we study the evolution of the correlated metallic state of LaNiO 3 in a series of LaNiO 3 /LaAlO 3 superlattices as a function of bilayer thickness. Spin-lattice relaxation measurements in an applied field of 6.55 T reveal two equal amplitude components: one with metallic (T linear) 1/T 1 and a second with a more complex T dependence. The metallic character of the slow relaxing component is only weakly affected by the LaNiO 3 thickness, while the fast component is much more sensitive, exhibiting the opposite temperature dependence (increasing toward low T) in the thinnest, most magnetic samples. The origin of this bipartite relaxation is discussed in terms of electronic phase separation.
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.
Electronic Structure and Transport Properties of Superlattices: La(1-X)SrxTiO3 (X =0, 0.20, 0.80, 1)
Journal of Nepal Physical Society, 2020
The conventional density functional theory (DFT) and dynamical mean field theory (DMFT) is used to study the structural, electronic and the Mott-Hubbard metal-insulator phase transition of the pristine and superstructures, La(1-x)SrxTiO3 (x = 0, 0.20, 0.80, 1). The electrical and thermal conductivities, Seebeck coefficient, Figure of merit are calculated using the BoltzTraP codes. The present study reveals that the direct band gap of 2.20 eV and indirect band gap ~2.0 eV at the Γ point in the Brillouin zone of SrTiO3 is upgraded to 3.423eV by using modified Beck-Johnson (mBJ) interaction potential. The metal-insulator transition (MIT) of LaTiO3 and the superlattice La(1-x)SrxTiO3 have been investigated by using conventional density functional theory (DFT) and dynamical mean field theory (DMFT). The Mott-Hubbard metal-insulator transitions for pristine LaTiO3 for a Coulombian parameter, U = 2.5 eV and the thermodynamic parameter β = 6 (eV)-1 are consistent with the experimental resul...
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.
Epitaxial growth of (111)-oriented LaAlO 3/LaNiO 3 ultra-thin superlattices
2012
Abstract The epitaxial stabilization of a single layer or superlattice structures composed of complex oxide materials on polar (111) surfaces is severely burdened by the reconstructions at the interface that commonly arise to neutralize the polarity. We report on the synthesis of high quality LaNiO 3/mLaAlO 3 pseudo cubic (111) superlattices on polar (111)-oriented LaAlO 3, the proposed complex oxide candidate for a topological insulating behavior.
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.