Transport measurements of the two-dimensional electron gas at the LaAlO3-SrTiO3 interface have found a density of carriers much lower than expected from the "polar catastrophe" arguments. From a detail density-functional study, we suggest how this discrepancy may be reconciled. We find that electrons occupy multiple subbands at the interface leading to a rich array of transport properties. Some electrons are confined to a single interfacial layer and susceptible to localization, while others with small masses and extended over several layers are expected to contribute to transport.
The electronic structures of the perovskite oxides, LaMnO 3 and CaMnO 3 , are studied using densityfunctional methods. Antiferromagnetic insulating (AFI) solutions are obtained for both compounds within the local-density approximation (LDA). For LaMnO 3 the Jahn-Teller distortion, found necessary for the AFI solution, produces occupied Mn͑z 2 2 1͒ orbitals pointed along the long, basal-plane Mn-O bonds. The large on-site Coulomb U and exchange J, obtained from "constrained" LDA calculations, U ഠ 8 10 eV and J ഠ 0.9 eV, indicate important correlation effects and yield large redistribution of the spectral weight within the LDA 1 U approach. PACS numbers: 71.20.Ps, 75.50.Ee The rich variety of electrical conduction exhibited by the transition-metal oxides has made them a lively area of research over the last several decades [1,2]. These include compounds such as NiO, the classic Mott insulator, Fe 3 O 4 which shows the Verwey charge-ordering transition, ReO 3 with room-temperature conductivity as large as that of copper, and the more recent high-T c copper-oxide superconductors. This Letter deals with the perovskite oxides, viz., the lanthanum manganite and its calcium doped alloys, La 12x Ca x MnO 3 , a topic of considerable renewed interest following the discovery of colossal magnetoresistance (CMR) in the La-Ca-Mn-O and related films [3,4]. Apart from the CMR effects, the unusual magnetic and conduction properties of the lanthanum manganites are well known. For example, La 12x Ca x MnO 3 is a ferromagnetic conductor in the range of 0.2 , x , 0.4, while the end members, x 0 or 1, are antiferromagnetic (AF) insulators [5]. The simultaneous occurrence of ferromagnetism and metallic conduction is qualitatively explained with Zener's idea of double exchange, where the presence of the Mn 31 -Mn 41 mixed valence ions is responsible for both ferromagnetic coupling and charge transport [6].Both LaMnO 3 and CaMnO 3 are AF insulators, but while in LaMnO 3 stacks of ferromagnetic (001) planes are arranged antiferromagnetically (type A, according to the Wollan-Koehler classification [7]), in CaMnO 3 , each Mn atom is surrounded by six nearest neighbors with AF alignment (type G). Here, we examine the electronic structure of these perovskites from density-functional calculations within the local spin-density approximation (LDA) as well as the "constrained" density-functional and the LDA 1 U approaches [8], using the linear muffin-tin orbitals (LMTO-ASA) method [9].An important structural feature of the perovskite oxides is the presence of the oxygen octahedra, which may be distorted. Both LaMnO 3 and CaMnO 3 form in the orthorhombic crystal structure [10], which is a distorted form of the cubic perovskite structure (Fig. 1). The O octahedron in LaMnO 3 contains a strong static JahnTeller (JT) distortion, while in CaMnO 3 this distortion is small. The JT distortion consists of a combination of the three modes that change the Mn-O bond lengths, viz., the breathing mode Q 1 , the basal-plane distortion mode Q 2 , and the octa...
In the original paper, figure 12(b) was incorrect and the caption of figure 12 was also erroneous. The correct figure and caption are shown below. E/t Figure 12. LDOS at the impurity site ρ 0A (top), the NN site ρ 0B (middle) and the next-NN site ρ 1A (bottom) obtained from equations (13) and (14) for different strengths of the impurity potential U 0 /t = 0, 2 and 5, denoted by black dashed, black solid and red dashed lines, respectively. As U 0 → ∞, the top LDOS goes to zero (except for the bound state beyond the top of the band whose energy goes to ∞), and the zero-mode state lives only on the B sublattice, as indicated from the middle and the bottom panels. The prominent zero-mode peak in the middle panel for U 0 /t = 5 will develop into a δ-function peak at E = 0 as the impurity potential U 0 → ∞.Abstract. We study the electronic structure of graphene with a single substitutional vacancy using a combination of the density-functional, tight-binding and impurity Green's function approaches. Density-functional studies are performed with the all-electron spin-polarized linear augmented plane wave (LAPW) method. The three sp 2 σ dangling bonds adjacent to the vacancy introduce localized states (Vσ ) in the mid-gap region, which split due to the crystal field and a Jahn-Teller distortion, while the p z π states introduce a sharp resonance state (Vπ ) in the band structure. For a planar structure, symmetry strictly forbids hybridization between the σ and the π states, so that these bands are clearly identifiable in the calculated band structure. As to the magnetic moment of the vacancy, the Hund's rule coupling aligns the spins of the four localized Vσ 1 ↑↓, Vσ 2 ↑ and Vπ ↑ electrons, resulting in an S = 1 state, with a magnetic moment of 2µ B , which is reduced by about 0.3µ B due to the anti-ferromagnetic spin polarization of the π band itinerant states in the vicinity of the vacancy. This results in the net magnetic moment of 1.7µ B . Using the Lippmann-Schwinger equation, we reproduce the well-known ∼1/r decay of the localized Vπ wave function with distance, and in addition, find an
Using density-functional calculations, we study the electronic structure of the purple bronze Li 0.9 Mo 6 O 17 , which has been proposed to be a paradigm system for the Luttinger liquid behavior. Our results show that the quasi-one-dimensional ͑1D͒ electron bands crossing the Fermi energy originate from the Mo atoms on the double zigzag chains with predominant Mo ͑d xy ͒ character and a Fermi surface that consists of two slightly warped planes, normal to the direction of the zigzag chains. The overall shape and dispersion of the bands as well as the calculated Fermi surface nesting vector are in excellent agreement with recent photoemission measurements. From constrained density-functional calculations of the Coulomb interactions and the calculated Fermi velocity, we estimate the values for the characteristic parameters of the Luttinger liquid, viz., the ratio of the spin-charge velocities to be v / v s Ϸ 1.8 and the anomalous dimension characterizing the Fermi surface discontinuity to be ␣ Ϸ 0.6. The general agreement of these values with experiments further strengthens the case for the lithium molybdenum purple bronze as a Luttinger liquid.
We show that the Rashba spin-orbit interaction in d electron solids, which originates from the broken inversion symmetry at surfaces or interfaces, is strongly dependent on the orbital characters of the bands involved. This is studied by developing a tight-binding model in the presence of a uniform perpendicular electric field and spin-orbit coupling. We argue that for valence electrons, the spin-orbit coupling strength scales only as the square of the atomic number. The electric field distorts the d orbitals through admixture of p and f states and also introduces new inter-site overlap parameters. Expressions for Rashba coefficients for the bands are obtained in both weak and strong spin-orbit interaction limits and are shown to be orbital dependent. The results are compared with first-principles calculations for model systems, showing good agreement. Our study demonstrates the orbital dependent gate control of the Rashba effect for the purposes of oxide electronics.
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