G. W. Morley, B. J. Herbert, S. M. Lee, K. Porfyrakis, T. J. S. Dennis, D. Nguyen-Manh, R. Scipioni, J. van Tol, A. P. Horsfield, A. Ardavan, D. G. Pettifor, J.… 展开作者
G. W. Morley, B. J. Herbert, S. M. Lee, K. Porfyrakis, T. J. S. Dennis, D. Nguyen-Manh, R. Scipioni, J. van Tol, A. P. Horsfield, A. Ardavan, D. G. Pettifor, J. C. Green, G. A. D. Briggs
The electron spin g- and hyperfine tensors of the endohedral metallofullerene Sc@C82 are anisotropic. Using electron spin resonance (ESR) and density functional theory (DFT), we can relate their principal axes to the coordinate frame of the molecule, finding that the g-tensor is not axially symmetric. The Sc bond with the cage is partly covalent and partly ionic. Most of the electron spin density is distributed around the carbon cage, but 5% is associated with the scandium d_yz orbital, and this drives the observed anisotropy.
In this paper we investigate the effect of Cd doping at ultra-low concentrations in SnO$_2$ both experimentally, by measuring the temperature dependence of the electric quadrupole hyperfine interactions with time-differential perturbed angular correlation (TDPAC) spectroscopy using $^{111}$Cd as probe nuclei, and theoretically, by performing first-principles calculations based on the density functional theory. TDPAC spectra were successfully analyzed with a time-dependent on-off model for the perturbation factor. These results show combined dynamic plus static interactions whose electric-field…
Dopants in silicon have been studied for many decades using optical and electron spin resonance (ESR) spectroscopy. Recently, new features have been observed in the spectra of dopants in isotopically enriched 28Si since the reduced inhomogeneous linewidth in this material improves spectral resolution. With this in mind, we measured ESR on exchange coupled phosphorus dimers in 28Si and report two results. First, a new fine structure is observed in the ESR spectrum arising from state mixing by the hyperfine coupling to the 31P nuclei, which is enhanced when the exchange energy is comparable to t…
We present the first findings of the vacancy-related centers identified by the electron spin resonance (ESR) and electrically-detected (ED) ESR method in the non-irradiated 6H-SiC nanostructure. This planar 6H-SiC nanostructure represents the ultra-narrow p-type quantum well confined by the δ-barriers heavily doped with boron on the surface of the n-type 6H-SiC (0001) wafer. The EDESR method by measuring the only magnetoresistance of the 6H SiC nanostructure under the high frequency generation from the δ-barriers appears to allow the identification of the silicon vacancy centers as well as the…
Multifrequency pulsed electron paramagnetic resonance (EPR) spectroscopy using S-, X-, Q- and W-Band frequencies (3.6, 9.7, 34, and 94 GHz, respectively) was employed to study paramagnetic coordination defects in undoped hydrogenated amorphous silicon (a-Si:H). The improved spectral resolution at high magnetic field reveals a rhombic splitting of the g-tensor with the following principal values: g_x=2.0079, g_y=2.0061 and g_z=2.0034 and shows pronounced g-strain, i.e., the principal values are widely distributed. The multifrequency approach furthermore yields precise ^{29}Si hyperfine data. De…
Synthesis of highly $^{13}$C isotope enriched azafullerene, C$_{59}$N embedded in C$_{60}$ is reported. $^{13}$C enriched fullerenes, produced with the Krätschmer-Huffmann process, were subject to a N$_{2}$ discharge that produces C$_{59}$N with a low probability. Raman spectroscopy indicates a homogeneous $^{13}$C distribution. Electron spin resonance measurement (ESR) proves that the C$_{59}$N concentration, 0.2 %, is similar as in non-enriched fullerenes. The ESR spectrum is simulated accurately with the known $^{14}$N and $^{13}$C hyperfine coupling constants. The material enables the nucl…
Bismuth (209Bi) is the deepest Group V donor in silicon and possesses the most extreme characteristics such as a 9/2 nuclear spin and a 1.5 GHz hyperfine coupling. These lead to several potential advantages for a Si:Bi donor electron spin qubit compared to the more common phosphorus donor. Previous studies on Si:Bi have been performed using natural silicon where linewidths and electron spin coherence times are limited by the presence of 29Si impurities. Here we describe electron spin resonance (ESR) and electron nuclear double resonance (ENDOR) studies on 209Bi in isotopically pure 28Si. ESR a…
We have studied the temperature behavior of the electron spin resonance (ESR) spectra of nitrogen (N) donors in n-type 6H SiC crystals grown by Lely and sublimation sandwich methods (SSM) with donor concentration of 10^17 cm^(-3) at T=60-150 K. A broad signal in the ESR spectrum was observed at T>=80 K with Lorentzian lineshape and gpar=2.0043(3), gper=2.0030(3), which was previously assigned in the literature to the N donors in the 1s(E) excited state. Based on the analysis of the ESR lineshape, linewidth and g-tensor we attribute this signal to the conduction electrons (CE). The emergence of…
We develop an analytical method for the processing of electron spin resonance (ESR) spectra. The goal is to obtain the distributions of trapped carriers over both their degree of localization and their binding energy in semiconductor crystals or films composed of regularly aligned organic molecules [Phys. Rev. Lett. v. 104, 056602 (2010)]. Our method has two steps. We first carry out a fine analysis of the shape of the ESR spectra due to the trapped carriers; this reveals the distribution of the trap density of the states over the degree of localization. This analysis is based on the reasonabl…
A computational study of the Electron Paramagnetic Resonance (EPR) $g$-tensors and hyperfine tensors of Li and Ga vacancies in LiGaO$_2$ is presented. Density Functinal Theory (DFT) calculations are carried out of the Ga and Li vacancies using the DFT+U approach in the charge states which carry an unpaired spin. In both vacancies the hole is located on one oxygen $p$-orbital adjacent to the vacancy. Apical and different basal plane O are considered. The magnetic resonance parameters of the defects are determined using the Gauge Including Projector Augmented Wave (GIPAW) method. The EPR spectra…
Rigorous extension of semilocal collinear functionals to noncollinear DFT using $SU(2)$ rotations
Helmholtz Institut Mainz（亥姆霍兹美因茨研究所）；GSI Helmholtzzentrum für Schwerionenforschung GmbH（GSI重离子研究中心有限公司）；Institut für Physik, Johannes Gutenberg-Universität Mainz（美因茨约翰内斯·古腾堡大学物理研究所）
The interaction between electronic and nuclear spins in the presence of external magnetic fields can be described by a spin Hamiltonian, with parameters obtained from first principles, electronic structure calculations. We describe an approach to compute these parameters, applicable to both molecules and solids, which is based on Density Functional Theory (DFT) and real-space, all-electron calculations using finite elements (FE). We report results for hyperfine tensors, zero field splitting tensors (spin-spin component) and nuclear quadrupole tensors of a series of molecules and of the nitroge…
A combined experimental/theoretical study of the EPR in irradiated $β$-Ga$_2$O$_3$ is presented. Four EPR spectra, two $S=1/2$ and two $S=1$, are observed after high-energy proton or electron irradiation. One of the S=1/2 spectra (EPR1) can be observed at room temperature and below and is characterized by the spin Hamiltonian parameters $g_b=2.0313$, $g_c=2.0079$, $g_{a*}=2.0025$ and a quasi isotropic hyperfine interaction with two equivalent Ga neighbors of $~\sim$14 G on $^{69}$Ga. The second (EPR2) is observed after photoexcitation (with threshold 2.8 eV) at low temperature and is character…
A DFT-based method is presented which allows the computation of all-electron NMR shifts of metallic compounds with periodic boundary conditions. NMR shifts in metals measure two competing physical phenomena. Electrons interact with the applied magnetic field (i) as magnetic dipoles (or spins), resulting in the Knight shift, (ii) as moving electric charges, resulting in the chemical (or orbital) shift. The latter is treated through an extension to metals of the Gauge Invariant Projector Augment Wave(GIPAW) developed for insulators. The former is modeled as the hyperfine interaction between the …
"Aftereffects'' Phenomenon in $^{111}$In($\rightarrow$$^{111}$Cd)-Implanted $α$-Al$_2$O$_3$ Single Crystals: Novel Approach Integrating Experimental Double-Model Analysis with Density-Functional Theory
Universidad Nacional de La Plata（拉普拉塔国立大学）；Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)（阿根廷国家科学研究委员会）；Universität Bonn（波恩大学）；Universidade Federal do Ceará（塞阿拉联邦大学）
