Electron-nuclear double resonance of deep-boron acceptors in silicon carbide

Electron-nuclear double resonance spectra of deep-boron acceptors in silicon carbide have been observed. The quadrupole and hyperfine interaction constants are determined. A sharp decrease of the quadrupole interaction and suppression of the anisotropic part of the hyperfine interaction, as compared with shallow-boron acceptors, are found. The observed effects are explained by the motion of holes inside the deep-boron acceptor. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 10, 803–808 (25 May 1996)     

On the hyperfine spectral lines of an atomic copper vapor laser

The hyperfine structure of energy levels of copper atom and its transition probabilities were considered. The resonance and metastable levels of the copper atom are split into hyperfine structures, due to the magnetic dipole moment and the electric quadrupole moment. In this paper, a succinct introduction to the relevant theory of the hyperfine spectral structure and experimental observations of elemental copper vapor laser is presented.     

Effect of the nuclear hyperfine field on the 2D electron conductivity in the quantum Hall regime

The effect of the nuclear hyperfine interaction on the dc conductivity of 2D electrons under quantum Hall effect conditions at filling factor ν=1 is observed for the first time. The local hyperfine field enhanced by dynamic nuclear polarization is monitored via the Overhauser shift of the 2D conduction electron spin resonance in AlGaAs/GaAs multiquantum-well samples. The experimentally observed change in the dc conductivity resulting from dynamic nuclear polarization is in agreement with a thermal activation model incorporating the Zeeman energy change due to the hyperfine interaction. The relaxation decay time of the dc conductivity is, within experimental error, the same as the relaxation time of the nuclear spin polarization determined from the Overhauser shift. These findings unequivocally establish the nuclear spin origins of the observed conductivity change. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 1, 58–63 (10 January 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

MgF2:Mn2+光谱、超精细常数和局部结构的关联

基于电子顺磁共振(EPR)超精细常数A_s确定键长的新方法和半自洽场d轨道理论，对MgF₂:Mn²⁺光谱和EPR超精细常数作出了统一解释.得到室温下MgF₂:Mn²⁺晶体中杂质中心Mn—F的键长为0.2124±0.0010nm. 关键词： 晶体场 电子顺磁共振 光学和磁学性质     

Effective spin spin interactions in the damped ferromagnets

Simanek's theory is extended by taking into account the nuclear spin excitations due to the motion of the electronic system. Damping of the magnons is found to be an extra criteria for having a finite interaction range for the nuclear spin system. The resonance excitation of Simanek's theory is due to the neglect of the second order in the hyperfine interaction.     

束缚施主电子与Si29核超精细作用的各向异性

本文利用Si中浅能级施主的有效质量波函数,计算了束缚施主电子与Si²⁹核超精细作用的等效自旋哈密顿量。超精细作用中不同谷的Bloch函数之间,相干效应非常明显,超精细作用的各向异性主要是由谷间相干效应决定的。在强场近似下求出了Si²⁹核的核磁共振频率的表示式,定量地解释了Feher的实验结果,并且可以由实验定出谷间磁偶极相互作用矩阵元。从正交干面波的观点出发进行了计算,与实验结果比较定出了导带底布洛赫函数中2P心态波函数的组合系数的大小为0.20。指出了利用双共振方法及其压力效应有可能测定导带底的波矢及有效质量波函数的各向异性分布。     

Phosphorus donors in highly strained silicon

The hyperfine interaction of phosphorus donors in fully strained Si thin films grown on virtual Si(1-x)Ge(x) substrates with x< or =0.3 is determined via electrically detected magnetic resonance. For highly strained epilayers, hyperfine interactions as low as 0.8 mT are observed, significantly below the limit predicted by valley repopulation. Within a Green's function approach, density functional theory shows that the additional reduction is caused by the volume increase of the unit cell and a relaxation of the Si ligands of the donor.     

Collapse in the Stoner-Wohlfarth noninteracting-particle model

A theory of Mössbauer spectra of noninteracting Stoner-Wohlfarth (SW) particles interacting with rf magnetic fields is developed. The theory makes it possible to calculate the absorption spectra for arbitrary frequency and amplitude of the rf field. The main features of the Stoner-Wohlfarth model are discussed. The Liouville superoperator formalism is used to generalize the results to the case of arbitrarily time-varying hyperfine fields at a nucleus. To understand the qualitative features of the collapse effect that are observed in the Mössbauer spectra of SW particles the particular case of a circularly polarized hyperfine field is studied, and an analytical expression is obtained describing the Mössbauer spectra for this case. An analysis is also made for weak rf magnetic fields and in this case the resonance behavior of the Mössbauer lines is traced as a function of the frequency of the rf field.     

E.S.R. study of the electron trapping centre in a single crystal of maleic acid irradiated at 77 K

Evidence for an electron trapping centre produced by ionizing radiations in a single crystal of maleic acid has been obtained by electron spin resonance. When the crystal is irradiated at 77 K several paramagnetic species are produced. One of them is the species in which the unpaired electron occupies the delocalized π orbital and interacts with the two vinylene protons. The hyperfine tensors of the two vinylene protons, which are typical of α proton coupling, are (-13·0, -8·5, -3·2) and (-6·4, -5·2, -1·9)G, respectively. The g tensor is (2·0043, 2·0040, 2·0024). The principal directions of the hyperfine and g tensors give information about the electron trapping centre in which the framework of the molecule is preserved. The probable structure of this centre is the delocalized carboxyl anion although the possibility of its protonated form cannot be completely excluded.     

Splitting of the electromagnetically induced transparency resonance on 85Rb atoms in strong magnetic fields up to the Paschen-Back regime

Electromagnetically induced transparency (EIT) resonance in strong magnetic fields of up to 1.7 kG has been investigated with the use of a 30-??m cell filled with an atomic rubidium vapor and neon as a buffer gas. The EIT resonance in the ?? system of the D₁ line of ⁸⁵Rb atoms has been formed with the use of two narrowband (??1 MHz) 795-nm diode lasers. The EIT resonance in a longitudinal magnetic field is split into five components. It has been demonstrated that the frequencies of the five EIT components are either blue- or red-shifted with an increase in the magnetic field, depending on the frequency ??_P of the probe laser. In has been shown that in both cases the ⁸⁵Rb atoms enter the hyperfine Paschen-Back regime in magnetic fields of >1 kG. The hyperfine Paschen-Back regime is manifested by the frequency slopes of all five EIT components asymptotically approaching the same fixed value. The experiment agrees well with the theory.     

Hyperfine interaction in a quantum spin chain

From an electron spin resonance measurement on a single crystal sample of theS=1 linear chain Heisenberg antiferromagnet Ni(C₃H₁₀N₂)₂NO₂ClO₄ (NINO) containing a small amount of Cu impurity atoms, we have observed two sets of four hyperfine lines, one of which has almost three times larger field splitting than the other. The hyperfine lines are well explained as arising from the hyperfine interaction between the Cu nuclear spin andthe Cu electron spin which interact with theS=1/2 degrees of freedom induced at the Ni sites by the quantum effect. A large anisotropy in the hyperfine constant is observed andanalyzed using a ligand field theory with covalency effects.     

Dependence of nuclear diffraction on the azimuthal angle: (002)- and (0010)-reflections of YIG

Nuclear diffraction of synchrotron radiation has been investigated using YIG single crystals in different scattering geometries. Time resolved quantum beat spectra of pure nuclear (002) and (0010) Bragg reflections were observed in a set-up where the hyperfine interaction was kept constant, while the azimuthal angle in the (001) surface between the [100] axis and the scattering plane (k _in,k _out) was varied. The time spectra were analyzed by means of the dynamical theory for coherent nuclear scattering. The results revealed the high sensitivity of this experimental technique on the complete set of hyperfine interaction parameters and on the specific geometrical conditions for nuclear diffraction of polarized γ-rays.     

The electron spin resonance spectra of the toluene,p-xylene and m-xylene anions

The electron spin resonance (e.s.r.) spectra of the anions of toluene, p-xylene and m-xylene have been studied and the proton hyperfine coupling constants determined. These are in excellent agreement with the predictions of Hückel molecular orbital theory.     

Two-dimensional hyperfine sublevel correlation spectroscopy: powder features for S=1/2, I=1

The lineshapes of two-dimensional magnetic resonance spectra of disordered or partially ordered solids are dominated by ridges of singularities in the frequency plane. The positions of these ridges are described by a branch of mathematics known as catastrophe theory concerning the mapping of one 2D surface onto another. We systematically consider the characteristics of HYSCORE spectra for paramagnetic centers having electron spin S=1/2 and nuclear spin I=1 in terms of singularities using an exact solution of the nuclear spin Hamiltonian. The lineshape characteristics are considered for several general cases: zero nuclear quadrupole coupling; isotropic hyperfine but arbitrary nuclear quadrupole couplings; coincident principal axes for the nuclear hyperfine and quadrupole tensors; and the general case of arbitrary nuclear quadrupole and hyperfine tensors. The patterns of singularities in the HYSCORE spectra are described for each case.     

Electron paramagnetic resonance spectroscopy of Cr 3+ in hexagonal Cs 2 NaGaF 6 crystals

Powder samples of hydrothermally grown Cr 3+ -doped Cs 2 NaGaF 6 crystals have been investigated with electron paramagnetic resonance spectroscopy at X - (9.5 v GHz) and Q -band (34 v GHz). Analysis of the spectra clearly demonstrates that there are two distinct Cr 3+ centres in the Cs 2 NaGaF 6 crystal, having nearly identical g factors, but differing largely from the viewpoint of their zero field splitting. By using the 53 Cr hyperfine spectra observed with electron nuclear double resonance spectroscopy, it is deduced that these centres have opposite signs for the zero field splitting. The spectroscopic properties of the Cr 3+ centres in the isostructural Cs 2 NaGaF 6 and Cs 2 NaAlF 6 crystals are compared and discussed.     

Simulations of Sisyphus cooling including multiple excited states

We extend the theory for laser cooling in a near-resonant optical lattice to include multiple excited hyperfine states. Simulations are performed treating the external degrees of freedom of the atom, i.e., position and momentum, classically, while the internal atomic states are treated quantum mechanically, allowing for arbitrary superpositions. Whereas theoretical treatments including only a single excited hyperfine state predict that the temperature should be a function of lattice depth only, except close to resonance, experiments have shown that the minimum temperature achieved depends also on the detuning from resonance of the lattice light. Our results resolve this discrepancy.     

Resonance internal conversion as a way of accelerating nuclear processes

A theory of resonance conversion (RC) is presented. It is shown that by resonance conversion being a natural extension of traditional internal conversion, into the subthreshold domain, in a number of cases, it strongly affects nuclear de-excitation. Moreover, as it concentrates transition strength in narrow bands corresponding to atomic spectral lines, it is a unique tool for accelerating nuclear processes. Along with the wellknown process of non-radiative nuclear excitation through electron NEET transition and the inverse RC process, resonance conversion provides convenient mathematics for a number of crossing-invariant processes involving a nucleus and electrons, excitation and de-excitation of nuclei, by a hyperfine magnetic field, spin mixing of nuclear states via an electron shell, a hyperfine interaction and magnetic anomalies in an atomic spectra, and the excitation of nuclei in collisions accompanied by the ionization of an electron shell, in muon decay in the orbit, etc. Mechanisms of isomer pumping via a laser-radiation-induced RC and of isomer energy triggering in a resonance laser radiation field are considered. An especially strong effect can be obtained in hydrogen-like ions, with practically no RC damping. The theory is also generalized to the case of discrete Auger transitions.     

Isotope shifts and hyperfine structure in the transitions of gadolinium

High-resolution resonance ionization mass spectrometry has been used to measure isotope shifts and hyperfine structure in all (J = 2-6) and the transitions of gadolinium (Gd I). Gadolinium atoms in an atomic beam were excited with a tunable single-frequency laser in the wavelength range of 422-429 nm. Resonant excitation was followed by photoionization with the 363.8 nm line of an argon ion laser and resulting ions were mass separated and detected with a quadrupole mass spectrometer. Isotope shifts for all stable gadolinium isotopes in these transitions have been measured for the first time. Additionally, the hyperfine structure constants of the upper states have been derived for the isotopes ^{155, 157} Gd and are compared with previous work. Using prior experimental values for the mean nuclear charge radii, derived from the combination of muonic atoms and electron scattering data, field shift and specific mass shift coefficients for the investigated transitions have been determined and nuclear charge parameters for the minor isotopes ^{152, 154} Gd have been calculated. Received 18 November 1999     

Atomic beam,optogalvanic and stored ion spectroscopy for radioactive isotopes

Systematic studies of the optical isotope shift and the hyperfine splitting of long chains of stable and radioactive isotopes were performed. The method applied was laser induced resonance absorption; the experimental techniques were the atomic beam method with fluorescence detection and the optogalvanic method. The theory of hyperfine splitting and isotope shift of atoms is reviewed in short with emphasis on the aspects interesting for nuclear physics and on the evaluation problem. The experimental methods are described and their key parameters sensitivity and resolution are discussed. Preliminary results on stored thorium ions are given. Sample results for the nuclear quantity δ<r ²> derived from atomic beam experiments with tin and strontium are presented.