Lattice normal modes and electronic properties of the correlated metal LaNiO3

Abstract

We use density functional theory (DFT) calculations to study the lattice vibrations and electronic properties of the correlated metal LaNiO3. To characterize the rhombohedral to cubic structural phase transition of perovskite LaNiO3, we examine the evolution of the Raman-active phonon modes with temperature. We find that the A1g Raman mode, whose frequency is sensitive to the electronic band structure, is a useful signature to characterize the octahedral rotations in rhombohedral LaNiO3. We also study the importance of electron-electron correlation effects on the electronic structure with two approaches which go beyond the conventional band theory (local spin density approximation): the local spin density+Hubbard U method (LSDA+U ) and hybrid exchange-correlation density functionals which include portions of exact Fock-exchange. We find the conventional LSDA accurately reproduces the delocalized nature of the valence states in LaNiO3 and gives the best agreement to the available experimental data on the electronic structure of LaNiO3. Based on our calculations, we show that the electronic screening effect from the delocalized Ni 3d and O-2p states mitigate the electronic correlations of the d 7 Ni cations, making LaNiO3 a weakly correlated metal.

Beta Detected NMR of LaAlO3

“…β-NMR is a magnetic resonance technique in which a laser polarized radioactive ion beam is implanted into the sample of interest. The most common isotope used, and the one used in this experiment, is 8 Li which undergoes a beta decay. The 8 Li nucleus has spin , gyromagnetic ratio , and electric quadrupole moment .…”

“…For this experiment, SLR measurements were performed with a pulsed beam of 8 Li, and no applied RF. Here, a pulse of 8 Li + is implanted into the sample, and then the asymmetry is measured as a function of time.…”

“…Here, a pulse of 8 Li + is implanted into the sample, and then the asymmetry is measured as a function of time. This provides information on the different relaxation mechanisms in the system.…”

“…As the cubic symmetry breaks, these octahedra become distorted, either elongating or compressing along the rotation axis. The phase transition in LAO can be characterized as second order with the order parameter given by the rotation angle of the AlO6 octahedra (φ) [1,7,8]. 27 Al and 139 La NMR has been performed on LaAlO3 above and below the phase transition.…”

“…In this paper, we report on investigations of the 8 Li spin lattice relaxation (SLR) in a LaAlO3 crystal in high magnetic field. The relaxation, while extremely slow, shows a systematic temperature dependence consistent with a phonon relaxation mechanism, probably facilitated by quadrupolar relaxation.…”