Polarization screening and induced carrier density at the interface of LaAlO3_3 overlayer on SrTiO3_3 (001)

We investigate the role of lattice polarization in determination of induced carrier density at the $n$-type interface of LaAlO$_3$ overlayer on SrTiO$_3$ (001) by carrying out density-functional-theory calculations. When no oxygen vacancy or defect is present, the magnitude of polarization screening in the LaAlO$_3$ layers is found to be correlated with the carrier charge induced at the interface. For the interfaces with a few LaAlO$_3$ layers, the induced charge carrier is compensated by the electrostatic screening and consequently its density remains far less than 0.5 electrons per unit cell.Comment: 4 pages, 4 figure

Electronic structure Fermi liquid theory of high Tc superconductors: Comparison of predictions with experiments

Predictions of local density functional (LDF) calculations of the electronic structure and transport properties of high T(sub c) superconductors are presented. As evidenced by the excellent agreement with both photoemission and positron annihilation experiments, a Fermi liquid nature of the 'normal' state of the high T(sub c) superconductors become clear for the metallic phase of these oxides. In addition, LDF predictions on the normal state transport properties are qualitatively in agreement with experiments on single crystals. It is emphasized that the signs of the Hall coefficients for the high T(sub c) superconductors are not consistent with the types of dopants (e.g., electron-doped or hole-doped) but are determined by the topology of the Fermi surfaces obtained from the LDF calculations

Electronic structure Fermi liquid theory of high T(sub c) superconductors: Comparison with experiments

For years, there has been controversy on whether the normal state of the Cu-oxide superconductors is a Fermi liquid or some other exotic ground state. However, some experimentalists are clarifying the nature of the normal state of the high T(sub c) superconductors by surmounting the experimental difficulties in producing clean, well characterized surfaces so as to obtain meaningful high resolved photoemission data, which agrees with earlier positron-annihilation experiments. The experimental work on high resolution angle resolved photoemission by Campuzano et al. and positron-annihilation studies by Smedskjaer et al. has verified the calculated Fermi surfaces in YBa2Cu3O7 superconductors and has provided evidence for the validity of the energy band approach. Similar good agreement was found for Bi2Sr2CaCu2O8 by Olson et al. As a Fermi liquid (metallic) nature of the normal state of the high T(sub c) superconductors becomes evident, these experimental observations have served to confirm the predictions of the local density functional calculations and hence the energy band approach as a valid natural starting point for further studies of their superconductivity

First-principles study of ultrathin (2 \times 2) Gd nanowires encapsulated in carbon nanotubes

Using density functional calculations, we investigate the structural and magnetic properties of ultrathin Gd and Gd-carbide nanowires (NWs) encapsulated in narrow carbon nanotubes (CNTs). The equilibrium geometry of an encapsulated (2 \times 2) Gd-NW is markedly different from that of bulk Gd crystals. The charge-density analysis shows pronounced spin-dependent electron transfer in the encapsulated Gd-NW in comparison with that of Gd-carbide NWs. We conclude that Gd-CNT hybridization is primarily responsible for both the structural difference and electron transfer in the encapsulated Gd-NW.Comment: 18 pages, 6 figures. (JCP version: 7 pages and small figures

Tunable charge donation and spin polarization of metal adsorbates on graphene using applied electric field

Metal atoms on graphene, when ionized, can act as a point charge impurity to probe a charge response of graphene with the Dirac cone band structure. To understand the microscopic physics of the metal-atom-induced charge and spin polarization in graphene, we present scanning tunneling spectroscopy (STS) simulations based on density functional theory calculations. We find that a Cs atom on graphene are fully ionized with a significant band bending feature in the STS, whereas the charge and magnetic states of Ba and La atoms on graphene appear to be complicated due to orbital hybridization and Coulomb interaction. By applying an external electric field, we observe changes in charge donations and spin magnetic moments of the metal adsorbates on graphene.Comment: 8 pages, 6 figure

Competition between structural distortion and magnetic moment formation in fullerene C20_{20}

We investigated the effect of on-site Coulomb interactions on the structural and magnetic ground state of the fullerene C$_{20}$ based on density-functional-theory calculations within the local density approximation plus on-site Coulomb corrections (LDA+$U$). The total energies of the high symmetry ($I_{h}$) and distorted ($D_{3d}$) structures of C$_{20}$ were calculated for different spin configurations. The ground state configurations were found to depend on the forms of exchange-correlation potentials and the on-site Coulomb interaction parameter $U$, reflecting the subtle nature of the competition between Jahn-Teller distortion and magnetic instability in fullerene C$_{20}$. While the non-magnetic state of the distorted $D_{3d}$ structure is robust for small $U$, a magnetic ground state of the undistorted $I_{h}$ structure emerges for $U$ larger than 4 eV when the LDA exchange-correlation potential is employed.Comment: 4 figures, 1 tabl

Collinear and non-collinear spin ground state of wurtzite CoO

Collinear and non-collinear spin structures of wurtzite phase CoO often appearing in nano-sized samples are investigated using first-principles density functional theory calculations. We examined the total energy of several different spin configurations, electronic structure and the effective magnetic coupling strengths. It is shown that the AF3-type antiferromagnetic ordering is energetically most stable among possible collinear configurations. Further, we found that a novel spiral spin order can be stabilized by including the relativistic spin-orbit coupling and the non-collinearity of spin direction. Our result suggests that a non-collinear spin ground state can be observed in the transition-metal-oxide nanostructures which adds an interesting new aspect to the nano-magnetism study.Comment: Phys. Rev. B (accepted