Search results for "Ground State"

On the Ground State Structure of Adsorbed Monolayers: Can One Find them by Monte Carlo Simulation?

2002

While the classical ground state structure of an atomic monolayer adsorbed at a noncorrugated perfectly flat substrate trivially is a triangular lattice, the spacing being the minimum of the interatomic potential, nontrivial structures occur on corrugated substrates. This problem is exemplified for the (100) face of a face-centered cubic crystal, varying both the density of the adsorbed monolayer and the strength of the potential due to the surface. Increasing the density beyond that of the commensurate c(2 x 2) structure, incommensurate patterns become stable with “heavy” walls (HW) oriented along the face diagonals [including the “crossing heavy walls” (CRHW) phase]. It is shown that slow…

Facilitating domain wall injection in magnetic nanowires by electrical means

2020

We investigate how to facilitate the injection of domain walls in chiral ferromagnetic nanowires by electrical means. We calculate the critical current density above which domain walls are injected into the nanowire depending on the material parameters and the source of interaction including spin-transfer torques as well as spin-orbit torques. We demonstrate that the Dzyaloshinskii-Moriya interaction can significantly reduce the required critical current to inject the types of domain walls favored by the Dzyaloshinskii-Moriya interaction. We find that in chiral magnets it is only possible to shed a single domain wall by means of spin-orbit torques, as they modify the ground state orientatio…

Electronic and crystallographic structure, hard x-ray photoemission, and mechanical and transport properties of the half-metallic Heusler compound Co…

2011

This work reports on the electronic and crystalline structure and the mechanical, magnetic, and transport properties of the polycrystalline Heusler compound Co${}_{2}$MnGe. The crystalline structure was examined in detail by extended x-ray absorption fine-structure spectroscopy and anomalous x-ray diffraction. The compound exhibits a well-ordered $L{2}_{1}$ structure as is typical for Heusler compounds with 2:1:1 stoichiometry. The low-temperature magnetic moment agrees well with the Slater-Pauling rule and indicates a half-metallic ferromagnetic state of the compound, as is predicted by ab initiocalculations. Transport measurements and hard x-ray photoelectron spectroscopy were performed t…

Temperature Dependence of Electronic and Magnetic Properties of (DOEO)<sub>4</sub>[HgBr<sub>4</sub>]·TCE Single Crystals

2015

The temperature dependence of electronic and magnetic properties of the organic charge-transfer salt (DOEO)4[HgBr4]·TCE was investigated using magnetometry. The magnetic susceptibility shows a maximum at 40 K followed by an onset of a pronounced increase at 70 K and a constant behavior above 120 K. Implications on the charge carrier density are discussed. Combining the magnetometry with resistivity and ESR measurements we propose a sequence of insulating, metallic and semiconducting behavior with increasing temperature. Our results indicate that (DOEO)4[HgBr4]·TCE is close to the boundary between an insulating and conducting ground state.

C-, N-, S-, and Fe-Doped TiO2 and SrTiO3 Nanotubes for Visible-Light-Driven Photocatalytic Water Splitting: Prediction from First Principles

2015

The ground state electronic structure and the formation energies of both TiO2 and SrTiO3 nanotubes (NTs) containing CO, NO, SO, and FeTi substitutional impurities are studied using first-principles calculations. We observe that N and S dopants in TiO2 NTs lead to an enhancement of their visible-light-driven photocatalytic response, thereby increasing their ability to split H2O molecules. The differences between the highest occupied and lowest unoccupied impurity levels inside the band gap (HOIL and LUIL, respectively) are reduced in these defective nanotubes down to 2.4 and 2.5 eV for N and S doping, respectively. The band gap of an NO+SO codoped titania nanotube is narrowed down to 2.2 eV …

Production of hydrogen negative ions in an ECR volume source: balance between vibrational excitation and ionization

2018

International audience; The operation of an ECR-driven (2.45 GHz) hydrogen negative ion source is studied. Electron densities and temperatures are investigated with electrostatic probes and negative ion densities are measured with laser photodetachment. Vacuum ultraviolet irradiance measurements are focused on molecular transitions to the ground state while high-resolution visible emission spectroscopy is used to study the transitions between excited states for both molecules and atoms. The standalone operation of the source is found to be more efficient in higher pressures (12 mTorr) where negative ion densities are as high as 4×109 cm−3. Further investigation on the operation of the sou…

Revealing the correlation between real-space structure and chiral magnetic order at the atomic scale

2017

We image simultaneously the geometric, the electronic, and the magnetic structures of a buckled iron bilayer film that exhibits chiral magnetic order. We achieve this by combining spin-polarized scanning tunneling microscopy and magnetic exchange force microscopy (SPEX) to independently characterize the geometric as well as the electronic and magnetic structures of nonflat surfaces. This new SPEX imaging technique reveals the geometric height corrugation of the reconstruction lines resulting from strong strain relaxation in the bilayer, enabling the decomposition of the real-space from the electronic structure at the atomic level and the correlation with the resultant spin-spiral ground sta…

A Novel Polyoxotungstate Containing atriangulo Ni3II Cluster with Ferromagnetic Exchange Interactions and anS= 3 Ground State

1992

Hydrogen in metals: Quantum aspects

1984

Hydrogen atoms are usually considered chemisorbed at well-defined sites on surfaces. We advocate a completelydifferent view, and demonstrate that chemisorbed hydrogen exhibits pronounced quantum effects. The hydrogen atom is to a large degree delocalized in both ground and excited-stated configurations: a proper description can only be given in terms of hydrogen energy bands. An analogous picture emerges for hydrogen isotopes (including muon) diffusing interstitially in bulk metals. The ground state there corresponds to a self-trapped situation: a localized impurity with an associated lattice distortion field. A powerful computational scheme is presented, which entails (i) the construction …

First principles calculations on CeO2 doped with Tb3+ ions

2019

This research was funded by the Latvian Council of Science (under the grant project lzp-2018/1-0147). Authors thank W. Chueh, J. Serra, R. Merkle, A. Popov for fruitful discussions.