A5013102246- Magnetic and transport properties of perovskites and related materials
- Advanced Condensed Matter Physics
- Physics of Superconductivity and Magnetism
- Electronic and Structural Properties of Oxides
- Rare-earth and actinide compounds
- Iron-based superconductors research
- Topological Materials and Phenomena
- Magnetic Properties of Alloys
- ZnO doping and properties
- Inorganic Chemistry and Materials
- 2D Materials and Applications
- Corporate Taxation and Avoidance
- Theoretical and Computational Physics
- Ferroelectric and Piezoelectric Materials
- Multiferroics and related materials
- Quantum and electron transport phenomena
- High-pressure geophysics and materials
- Superconductivity in MgB2 and Alloys
- Crystal Structures and Properties
- Magnetic properties of thin films
- Copper-based nanomaterials and applications
- Quantum, superfluid, helium dynamics
- Transition Metal Oxide Nanomaterials
- Ga2O3 and related materials
- Magneto-Optical Properties and Applications
University of British Columbia
2014-2024
Max Planck - University of Ottawa Centre for Extreme and Quantum Photonics
2012
University of Groningen
2001-2002
M.N. Mikheev Institute of Metal Physics
1996-1999
Russian Academy of Sciences
1997-1999
The understanding of the origin superconductivity in cuprates has been hindered by apparent diversity intertwining electronic orders these materials. We combined resonant x-ray scattering (REXS), scanning-tunneling microscopy (STM), and angle-resolved photoemission spectroscopy (ARPES) to observe a charge order that appears consistently surface bulk, momentum real space within one cuprate family, Bi <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow>...
We introduce a path to possibly new class of magnetic materials whose properties are determined entirely by the presence low concentration specific point defects in their crystal structure. Using model Hamiltonian and ab-initio band structure methods we demonstrate that even large gap nonmagnetic as simple CaO can exhibit extraordinary like half metallic ferromagnetism upon introducing small Ca vacancies. show such will initially bind introduced charge carriers at neighboring sites depending...
We study a model for the metal-insulator ($M\text{\ensuremath{-}}I$) transition in rare-earth-element nickelates $R{\mathrm{NiO}}_{3}$, based upon negative charge transfer energy and coupling to rocksaltlike lattice distortion of ${\mathrm{NiO}}_{6}$ octahedra. Using exact diagonalization Hartree-Fock approximation we demonstrate that electrons couple strongly these distortions. For small distortions system is metallic, with ground state predominantly ${d}^{8}L$ character, where...
We study Na2IrO3 by ARPES, optics, and band structure calculations in the local-density approximation (LDA). The weak dispersion of Ir 5d-t2g manifold highlights importance structural distortions spin-orbit coupling (SO) driving system closer to a Mott transition. detect an insulating gap {\Delta}_gap = 340 meV which, at variance with Slater-type description, is already open 300 K does not show significant temperature dependence even across T_N ~ 15 K. An LDA analysis inclusion SO Coulomb...
We demonstrate with LSDA $+U$ calculations that x-ray scattering at the $K$ edge of Mn is sensitive to orbital ordering in one energy range and Jahn-Teller distortion another. Contrary what suggested by atomic or cluster models used date we show band structure effects rather than local Coulomb interactions dominate polarization dependence therefore it nearest neighbor bond length distortions next occupation. Based on this propose a new mechanism for manganates which suggest also applicable...
We present a first-principles study of spin-orbit coupling effects on the Fermi surface Sr2RuO4 and Sr2RhO4. For nearly degenerate bands, leads to dramatic change with respect nonrelativistic calculations; as evidenced by comparison experiments Sr2RhO4, it cannot be disregarded. Sr2RuO4, modifications are more subtle but equally in detail: Spin-orbit induces strong momentum dependence, normal RuO2 planes, for both orbital spin character low-energy electronic states. These findings have...
High quality thin films of the ferromagnetic semiconductor EuO have been prepared and were studied using a new form spin-resolved spectroscopy. We observed large changes in electronic structure across Curie metal-insulator transition temperature. found that these are caused by exchange splitting conduction band state, which is as 0.6 eV. also present strong evidence bottom consists mainly majority spins. This implies doped charge carriers practically fully spin polarized.
The charge-ordered insulating state of ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ below the Verwey transition temperature has been studied by modified local density approximation with Coulomb interaction correction method. charge ordering is found to be a stable solution an energy gap value 0.34 eV (the experimental 0.14 eV) in contrast uniform metallic given standard spin-density approximation. calculated effective intersite well screened (V=0.18 eV). It was shown that change electrostatic...
The electronic structure of Bi2Se3 is studied by angle-resolved photoemission and density functional theory. We show that the instability surface properties, observed even in ultra-high-vacuum conditions, can be overcome via in-situ potassium deposition. In addition to accurately setting carrier concentration, new Rashba-like spin-polarized states are induced, with a tunable, reversible, highly stable spin splitting. Ab-initio slab calculations reveal these Rashba state derived from 5QL...
We describe a possible pathway to new magnetic materials with no conventional elements present. The substitution of nitrogen for oxygen in simple nonmagnetic oxides leads holes N 2p states which form local moments. Because the very large Hund's rule coupling Nitrogen and O electrons rather extended spatial extent wave functions these are predicted be ferromagnetic metals or small band gap insulators. Experimental studies support theoretical calculations regard basic electronic structure...
Transition-metal substitution in Fe pnictides leading to superconductivity is usually interpreted terms of carrier doping the system. We report on a density functional calculation local substitute electron and demonstrate that substitutions like Co Ni for do not dope but rather are isovalent Fe. find extra $d$ electrons almost totally located within muffin-tin sphere substituted site. suggest act more random scatterers scrambling momentum space washing out parts Fermi surface.
From first-principles calculations we investigate the electronic structure and magnetic properties of $\mathrm{EuO}$ under hydrostatic stress appropriate biaxial for epitaxial films. There is a complex interdependence $\mathrm{O}\phantom{\rule{0.3em}{0ex}}2p$ $\mathrm{Eu}\phantom{\rule{0.3em}{0ex}}4f$ $5d$ bands on magnetism in $\mathrm{EuO}$, decreasing lattice parameters an ideal method to increase Curie temperature ${T}_{c}$. Compared pressure, out-of-plane compensation that available...
We study the manipulation of spin polarization photoemitted electrons in Bi2Se3 by spin- and angle-resolved photoemission spectroscopy. General rules are established that enable controlling photoelectron spin-polarization. demonstrate ± 100% reversal a single component measured spin-polarization vector upon rotation light polarization, as well full three-dimensional varying experimental configuration photon energy. While material-specific density-functional theory analysis is needed for...
Substitutional alloying elements significantly affect the recrystallization and austenite-ferrite phase transformation rates in steels. The atomistic mechanisms of their interaction with interfaces are still largely unexplored. Using density functional theory, we determine segregation energies between commonly used Σ5 (013) tilt grain boundary bcc iron. We find a strong solute-grain for Nb, Mo, Ti that is consistent experimental observations effects these on delaying austenite-to-ferrite...
We propose a microscopic description of the bond-disproportionated insulating state in bismuth perovskites $X{\mathrm{BiO}}_{3}$ ($X=\text{Ba},\text{Sr}$) that recognizes bismuth-oxygen hybridization as dominant energy scale. It is demonstrated by using electronic structure methods breathing distortion accompanied spatial condensation hole pairs into local, molecularlike orbitals ${A}_{1g}$ symmetry composed O-$2{p}_{\ensuremath{\sigma}}$ and Bi-$6s$ atomic collapsed ${\mathrm{BiO}}_{6}$...
We have developed the numerical software package $chinook$, designed for simulation of photoemission matrix elements. This quantity encodes a depth information regarding orbital structure underlying wavefunctions from which occurs. Extraction this is often nontrivial, owing to influence experimental geometry and photoelectron interference, precluding straightforward solutions. The $chinook$ code has been simulate predict ARPES intensity measured arbitrary configuration, including...
Motivated by the recently renewed interest in superconducting bismuth perovskites, we investigate electronic structure of parent compounds ABiO$_{3}$ (A= Sr, Ba) using $ab$ $initio$ methods and tight-binding (TB) modeling. We use density functional theory (DFT) local approximation (LDA) to understand role various interactions shaping bandstructure near Fermi level. It is established that interatomic hybridization involving Bi-$6s$ O-$2p$ orbitals plays most important role. Based on our DFT...
Adding the local Coulomb repulsion to density approximation, so-called $\mathrm{LDA}+U$ scheme, leads us predict a first order transition from singlet semiconductor ferromagnetic metal in FeSi with increasing magnetic field. Extensions finite temperature lead interpretation that anomalous behavior at room and zero field arises proximity critical point of this transition. This may be accessible currently available fields.
We have performed ab initio calculations of exchange couplings in the layered vanadates ${\mathrm{CaV}}_{2}{\mathrm{O}}_{5}$, ${\mathrm{MgV}}_{2}{\mathrm{O}}_{5}$, ${\mathrm{CaV}}_{3}{\mathrm{O}}_{7}$, and ${\mathrm{CaV}}_{4}{\mathrm{O}}_{9}$. The uniform susceptibility Heisenberg model with these is then calculated by quantum Monte Carlo method; it agrees well experimental measurements. Based on our results we naturally explain unusual magnetic properties materials, especially huge...
The role of Co substitution in the low-energy electronic structure $\mathrm{Ca}({\mathrm{Fe}}_{0.944}{\mathrm{Co}}_{0.056}{)}_{2}{\mathrm{As}}_{2}$ is investigated by resonant photoemission spectroscopy and density-functional theory. $3d$ state center mass observed at 250 meV higher binding energy than that Fe, indicating possesses one extra valence electron Fe are same oxidation state. Yet, significant character detected for Bloch wave functions chemical potential, revealing electrons part...
We have used density-functional theory to calculate activation energies for diffusion of Al, Ca, and several rare-earth (RE) elements in Mg. The predicted solute-vacancy binding exchange increase decrease, respectively, with increasing solute size. Using the eight-frequency model hcp lattices we determined correlation factors each solute. Both Ca all RE exhibit significant effects whose temperature dependence can be described by an Arrhenius behavior. energy, which these solutes still...
The detection of quantum oscillations in the electrical resistivity $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.5}$ provides evidence for existence Fermi-surface pockets an underdoped cuprate. We present a theoretical study electronic structure $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ aimed at establishing nature these pockets---i.e., $\mathrm{Cu}{\mathrm{O}}_{2}$ plane vs CuO chain or BaO. argue that electron...