Optical study of strained ultrathin films of strongly correlatedLaNiO3

Abstract

An optical study of fully strained ultrathin LaNiO3 films is presented and compared with LDA+DMFT calculations. LaNiO3 films were grown by pulsed laser deposition on LaAlO3 and SrTiO3 substrates which provide compressive and tensile strain, respectively. Optical conductivity data show a Drude peak with a spectral weight that is significantly reduced compared to that obtained from LDA calculations. The extended Drude analysis reveals the presence of a pseudogap around 80 meV for the film on SrTiO3 and near 40 meV, at low temperature only, for the film on LAO. An unusual temperature dependence of the optical conductivity is observed, with the Drude plasma frequency increasing by up to 20% at low temperature due to spectral weight transfer from bands lying 2-4 eV below the Fermi energy. Such a strong temperature dependence of the Drude spectral weight has previously been reported for correlated electron systems in which a phase transition is present. In LNO however, no phase transition is observed.

Electronic structure and orbital polarization of LaNiO3with a reduced coordination and under strain: A first-principles study

“…Ionic movements make polarization slightly smaller and larger under the zero and +3% strain, respectively, with respect to the unrelaxed results (solid red line with open boxes). It is found that the relaxation-induced change becomes much larger in the compressively strained situation, which is attributed to the large ionic displacement along the out-of-plane direction caused by the compressive in-plane strain, and the volume conservation often being observed in the related materials 12,18 . In the zero strain case, the optimized distance between Ni and apical oxygen is ∼ 2.04Å .…”

“…Vacuum layer thickness is of 7.0Å which is large enough to make the basis function overlap negligible. While the polar surface may not be well stabilized in general, these instability can be compensated by the large covalency in the nickelates 11,12,17,18 . The geometry relaxation has been performed with the force criterion of 10 −3 Hartree/Bohr.…”

“…that remains metallic at all temperatures 1,10 . As a result, thin film LNO and LNO-based heterostructures have been studied under various strained conditions to control the correlation strength and the metalinsulator phase transition [11][12][13][14] in an effort to find possible high temperature superconductivity 15 and conductivity enhancement 16 . Strain affects most strongly the orbital character of the nickelates 15,[17][18][19][20] .…”

Quantifying electronic correlation strength in a complex oxide: A combined DMFT and ARPES study ofLaNiO3

“…LaNiO 3 has already been characterized experimentally via ARPES [14][15][16], optical conductivity [17][18][19], and thermodynamic measurements [20][21][22], as well as theoretically with DFT [23][24][25], DFT + DMFT [6,8,[26][27][28][29], and model system [30][31][32] calculations, and a variety of measurements of m /m have previously appeared (to be discussed more later). ARPES offers a particularly direct measure of a material's mass enhancement via momentum-resolved access to the electronic Green's function, which is the fundamental quantity that characterizes electron propagation in a material:…”

Lattice normal modes and electronic properties of the correlated metal LaNiO3

“…We do find one subtle caveat: the Ni e g states experimentally exhibit dynamical correlation effects, which we are unable to capture in either the LSDA, LSDA+U , or hybrid functionals. This enhanced spectral weight at the Fermi level has recently been reproduced experimentally and through LDA+dynamical meanfield theory (DMFT) calculations, [72][73][74] where a dynamic (frequency-dependent) treatment of the Ni 3d electronelectron interactions leads to an enhanced effective mass and optical conductivity.…”