Electronic properties of LaAlO3/SrTiO3 n-type interfaces: A GGA+U study

The role of electronic correlation effects for a realistic description of the electronic properties of LaAlO3/SrTiO3 heterostructures as covered by the on-site Coulomb repulsion within the GGA+U approach is investigated. Performing a systematic variation of the values of the Coulomb parameters applied to the Ti 3d and La 4f orbitals we put previous suggestions to include a large value for the La 4f states into perspective. Furthermore, our calculations provide deeper insight into the band gap landscape in the space spanned by these Coulomb parameters and the resulting complex interference effects. In addition, we identify important correlations between the local Coulomb interaction within the La 4f shell, the band gap, and the atomic displacements at the interface. In particular, these on-site Coulomb interactions influence buckling within the LaO interface layer, which via its strong coupling to the electrostatic potential in the LAO overlayer causes considerable shifts of the electronic states at the surface and eventually controls the band gap.Comment: 14 pages, 9 figure

Oxygen vacancies and hydrogen doping in LaAlO3/SrTiO3 heterostructures: electronic properties and impact on surface and interface reconstruction

We investigate the effect of oxygen vacancies and hydrogen dopants at the surface and inside slabs of LaAlO3, SrTiO3, and LaAlO3/SrTiO3 heterostructures on the electronic properties by means of electronic structure calculations as based on density functional theory. Depending on the concentration, the presence of these defects in LaAlO3 slab can suppress the surface conductivity. In contrast, in insulating SrTiO3 slabs already very small concentrations of oxygen vacancies or hydrogen dopant atoms induce a finite occupation of the conduction band. Surface defects in insulating LaAlO3/SrTiO3 heterostructure slabs with three LaAlO3 overlayers lead to the emergence of interface conductivity. Calculated defect formation energies reveal strong preference of hydrogen dopant atoms for surface sites for all structures and concentrations considered. Strong decrease of the defect formation energy of hydrogen adatoms with increasing thickness of the LaAlO3 overlayer and crossover from positive to negative values, taken together with the metallic conductivity induced by hydrogen adatoms, seamlessly explains the semiconductor-metal transition observed for these heterostructures as a function of the overlayer thickness. Moreover, we show that the potential drop and concomitant shift of (layer resolved) band edges is suppressed for the metallic configuration. Finally, magnetism with stable local moments, which form atomically thin magnetic layers at the interface, is generated by oxygen vacancies either at the surface or the interface, or by hydrogen atoms buried at the interface. In particular, oxygen vacancies in the TiO2 interface layer cause drastic downshift of the 3d e_g states of the Ti atoms neighboring the vacancies, giving rise to strongly localized magnetic moments, which add to the two-dimensional background magnetization.Comment: 15 pages, 17 figure

Prediction of thermodynamic properties of natural gases using Monte Carlo simulations

In this paper an applications of Monte-Carlo simulation in natural gas production is presented. We have investigated model of natural gas of the Bavlinskoye deposit located in the southeast of the Republic of Tatarstan. For this natural gas and for pure methane and ethane gases we have obtained thermal expansivity, isothermal compressibility, compressibility factor, heat capacity, Joule-Thompson coefficient and density at pressures up to 110 MPa at deposit temperature (463 K). Also we have obtained vapor pressures and liquid-vapor phase diagrams. Simulated properties for methane are in a good agreement with available experimental data

Structural and electronic properties of heterointerfaces composed of complex ferroelectric oxides

The reported study was funded by RFBR according to the research project № 18-32-00595

Towards high-temperature quasi-two-dimensional superconductivity

© 2018 American Physical Society. The demonstration of a quasi-two-dimensional electron gas (2DEG) and superconducting properties in LaAlO3/SrTiO3 heterostructures has stimulated intense research activity in the last ten years. The 2DEG has unique properties that are promising for applications in all-oxide electronic devices. The superconductivity in such heterostructures has been observed below 300 mK. For superconductivity applications it is desirable to have more wide temperature of the existence range and the ability to control superconducting properties by external stimulus. Based on first-principles calculations and theoretical consideration we show that all-oxide heterostructures incorporating a ferroelectric constituent, such as BaTiO3/La2CuO4, allow creating 2DEG. We predict a possibility of a high-temperature quasi-two-dimensional superconducting state. This state could be switchable between superconducting and conducting states by ferroelectric polarization reversal. We also discuss that such structures must be more simple for preparation. The proposed concept of a ferroelectrically controlled interface superconductivity offers the possibility to design novel electronic devices

Density functional theory calculations on azobenzene derivatives: a comparative study of functional group effect

© 2014, Springer-Verlag Berlin Heidelberg. Density functional theory (DFT) calculations have been used to investigate the structural properties, dipole moments, polarizabilities, Gibbs energies, hardness, electronegativity, HOMO/LUMO energies, and chemical potentials of trans and cis configurations of eight para-substituted azobenzene derivatives. All properties have been obtained using the B3LYP functional and 6-31++G(d,p) basis set. The planar structures have been obtained for all optimized trans configurations. The energy difference between trans and cis configurations for considered derivatives was found to be between 64.2–73.1 kJ/mole. It has been obtained that the p-aminodiazo-benzene (ADAB) has the difference in the dipole moments between trans and cis forms higher than for trans and cis azobenzene

Structural, electronic and optical properties of heterointerfaces based on antiferromagnet LaMnO3 and ferroelectrics isostructural to BaTiO3

The reported study was funded by Russian Scientific Foundation according to the research project No. 18-12-00260

Electrical properties of heterointerfaces composed of complex ferroelectric oxides: an experimental investigation

The reported study was funded by RFBR according to the research project № 18-32-00595

Electronic properties of LaAlO<inf>3</inf>/SrTiO<inf>3</inf> n-type interfaces: A GGA+U study

© 2017 IOP Publishing Ltd. Printed in the UK.LaAlO3/SrTiO3 heterostructures as covered by the on-site Coulomb repulsion within the GGA U approach is investigated. Performing a systematic variation of the values of the Coulomb parameters applied to the Ti 3d and La 4f orbitals we put previous suggestions to include a large value for the La 4f states into perspective. Furthermore, our calculations provide deeper insight into the band gap landscape in the space spanned by these Coulomb parameters and the resulting complex interference effects. In addition, we identify important correlations between the local Coulomb interaction within the La 4f shell, the band gap, and the atomic displacements at the interface. In particular, these on-site Coulomb interactions influence buckling within the LaO interface layer, which via its strong coupling to the electrostatic potential in the LAO overlayer causes considerable shifts of the electronic states at the surface and eventually controls the band gap