Low-temperature franz-keldysh oscillations in uniaxially stressed germanium

In this paper we report some typical results of high-field electroreflectance on single crystals of germanium, stressed uniaxially along the (001) direction. Measurements were made at 10°K near the fundamental direct edge. The electric field was applied by Schottky barrier. Franz-Keldysh oscillations exhibiting up to twenty peaks enabled us to determine the broadening parameter Γ = 1.4 meV and the ratio of the reduced masses μ₀₂/μ₀₁ = 0.97.     

Resonant states of shallow acceptors in uniaxially deformed germanium

The states of shallow acceptors in uniaxially deformed germanium are studied theoretically. A non-variational numerical computational method is developed for determining the energy and wave functions of localized states of holes in the acceptor field as well as the states of the continuous spectrum (including resonant impurity states). The dependence of the energy of the lower resonant state on strain is studied. It is found that this state is formed from the excited 4Γ ₈ ⁺ state with a binding energy of 1.3 meV (in the absence of deformation) and not from the ground state. The results presented in this work may be useful in the study of the conditions for the generation of far IR radiation in deformed p-Ge, which involves optical transitions between resonant and localized acceptor states.     

Far-infrared photoconductivity spectra of quenched-in acceptors in germanium: Chemical effects on the SA1 acceptors

Far-I.R. photoconductivity reveals the existence of at least four different kinds of SA₁ acceptors in germanium quenched from T > 800 each acceptor producing two or more hydrogenic excitation line series. One acceptor is correlated with the presence of Ni, another one with strong Cu contamination. The two other acceptors, which we call ‘normal’ and ‘shifted’, occur in samples quenched without intentional doping. The experiments indicate that the SA₁ acceptors in germanium are impurity complexes involving fast diffusing elements. We discuss a model according to which the SA₁ acceptors would be interstitial-substitutional pairs of transition metals. In particular, we propose to assign the ‘normal’ SA₁ acceptors to Fe_I-Cu_S pairs.     

A contribution to the question of thermal acceptors in germanium

The motion and decay of thermal acceptors in germanium was studied using the method of saturation and the extraction of solid germanium by means of a liquid alloy of Ge/Sn. The qualitative results obtained confirm that the production of thermal acceptors in germanium is conditioned by the presence of copper and in addition prove the applicability of this method to the solution of similar problems.     

Binding energy of positively charged acceptors in germanium - a Green's function Monte Carlo calculation

Recent spectroscopic measurements in Ge reveal positively charged acceptors consisting of an extra hole bound to a double or triple acceptor. Using the effective-mass approximation and a pseudo-atom model which permits up to four holes in the 1s ground state, we calculate the binding energies of these positively charged acceptors by the Green's function Monte Carlo method. For double acceptors the results of the pseudo-atom model compare favorably with experiments, whereas for triple acceptors the differences are significant.     

弛豫与关联效应对NII离子2s22p3s3P1—2s22p21D2与2s22p3s1P1—2s22p23P0,1,2自旋禁戒跃迁概率的影响

用多组态Dirac-Fock方法，并系统考虑相对论效应、电子关联、弛豫效应等重要贡献，计算了NII离子2s22p3s 3P1—2s22p21D2和2s22p3s 1P1—2s22p23P0,1,2自旋禁戒跃迁概率和振子强度-通过比较计算证实：弛豫和关联效应对禁戒跃迁概率的影响非常大，考虑了这些效应后，计算结果有显著的改善-由跃迁概率和振子强度的计算值推断，2s22p3s 3P1—2s22p21D2的谱线强度应该比原有的理论预言值小- 关键词： 跃迁概率 多组态Dirac-Fock方法     

Improved measurement of the 1s2s 1S0-1s2p 3P1 interval in heliumlike silicon

Using colinear fast-beam laser spectroscopy with copropagating and counter-propagating beams we have measured the 1s2s 1S0-1s2p 3P1 intercombination interval in 28Si12+ with the result 7230.585(6) cm{-1}. The experiment made use of a dual-wavelength, high-finesse, power build-up cavity excited by single-frequency lasers at 1319 and 1450 nm. The result will provide a precision test of ab initio relativistic many-body atomic theory at moderate Z.     

Measurement of cross-section of excitation transfer from 3s2 to 4s1 and 5s1 energy levels of neon

Collision induced non-radiative transitions in neon plasma have been studied using high intra-cavity radiation field of a 633 nm He-Ne laser. The transitions, induced from 3s ₂ energy level to 4s₁ and 5s₁ groups of energy levels, have been detected as changes in intensities of the spectral lines originating from these energy levels. From these intensity measurements, the quantities governing the transitions i.e. (i)S ₃ ^e /S _3RT , the ratio of the probabilities of electronic deexcitation to the total radiative deexcitation of energy level 3 (ii) 〈r ₂₃ ^e v _e〉, rate of excitation transfer per particle and (iii)S ₂₃ ^e , the total probability for excitation transfer from level 2 to level 3 at a certain value of electron density have been calculated.     

Lineshape of Ne 1s photoionization satellite [1s2s](3S)3s and its valence Auger decay spectrum

Lineshape of Ne1s photoionization satellite $\text{[1s2s](}{}^3\text{S)3s(}{}^2\text{S)}$ and lineshapes of corresponding low-energy Auger spectra are calculated using the Many-Body Perturbation Theory. The results obtained reproduce the experimentally observed asymmetrical lineshape of photoelectron satellite and its intensity.     

Triplet-singlet interaction in the 1s 2s3S1 hyperfine splitting of he-like Li+

The hyperfine structure (hfs) interaction between the metastable 2³ S ₁ and 2¹ S ₀ states in^{6, 7}Li⁺ causes very small equal and opposite energy level shifts,δ, in the two levels having the same total angular momentum quantum numberF=I. This amounts to 12ppm with respect to the total hfs splitting of 30 GHz for the⁷Li⁺ 2³S₁ state and has been measured for the first time directly for the case of a core-free electronic system by combined laser-microwave spectroscopy. A new calculation ofδ with accurate integral-transform 2¹ S ₀ and 2³S₁ wave functions is reported. Configuration interactions and electron exchange and correlation effects, which differ for parallel (³ S ₁) and antiparallel (¹ S ⁰) spins, are treated in detail in order to obtain very good agreement between measured and theoretical values for this tiny perturbation. A complete understanding ofδ is indispensable for extracting fundamental constants from two-electron spectroscopic data.     

类铍离子1s22s2p 3P1, 2 能级之间的磁偶极跃迁

用多组态Dirac-Fock和相对论组态相互作用的扩展优化能级方法,在计算中包含了Breit相互作用,真空极化,自能以及有限核质量修正,计算了核电荷数从Z=6到80的类铍离子等电子序列的1s22s2p 3P1, 2的精细结构能级,磁偶极跃迁几率和振子强度。结果与目前可靠的结果在其不确定度范围内符合得很好,另外也得到一些与其他早期理论计算不同的结果。     

Laser spectroscopy of the 1s22s2p 3P2-3P1 transition in beryllium-like argon using the Oxford EBIT

A study of the 1s²2s2p ³P₂-³P₁ fine-structure transition in beryllium-like argon is planned on the Oxford electron beam ion trap (EBIT), using laser-induced resonance. This transition wavelength was measured previously as 594.373(4) nm, which is accessible using a dye laser. The ions are produced and excited in the EBIT and are confined during laser irradiation using the magnetic trapping mode. The ³P₂ level population is depleted by the laser and by subsequently monitoring the emitted fluorescence a laser resonance signal can be obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Size dependence of ground-state energy of the excitons in spherical Y2O3

The exciton energies of rare earth oxides (Ln₂O₃) have rarely been calculated by the theory. Experimentally, the blue-shift of exciton energy in nanocrystals deviates from the traditional size confinement effect. Herein, the dependence of the ground-state energy of an exciton in Y₂O₃ spheres on particle radius was calculated by using a variational method. In the model, an exciton confined in a sphere surrounded by a dielectric continuum shell was considered. The ground-state energy of exciton comprises kinetic energy, coulomb energy, polarization energy and exciton–phonon interaction energy. The kinetic and coulomb energy were considered by the effective mass and the dielectric continuum and the exciton–phonon interaction energy was given by the intermediate coupling method. The numerical results demonstrate that the present model is roughly consistent with the experimental results. The confinement effect of the kinetic energy is dominant of the blue-shift of the exciton energy in the region of R < 5 nm, while confinement effect of the coulomb energy is dominant of the blue-shift of the exciton energy in the region of R > 5 nm. The polarization energy contributes largely to the exciton energy as the particle size is smaller than ~ 10 nm, while the exciton–phonon interaction energy takes only a little contribution in all the range.     

钪原子的自电离里德伯能级3d4s(~1D_2)nf~2D_(3/2),3d4s(~1D_2)nf~2F_(5/2)和3d4s(~1D_2)np~2D_(3/2)的理论研究

在多通道量子亏损理论框架下,利用相对论多通道理论,分别在冻结实近似和考虑偶极极化下计算钪原子的Jπ=(3/2)-,(5/2)-的三个收敛于[Ar]3d4s(1D2)的自电离里德伯系列的能级.对3d4s(1D2)np2D3/2和3d4s(1D2)nf2F5/2这两个系列,计算结果表明,考虑偶极极化效应后,理论计算和实验测量的量子数亏损之差普遍小于0.01.而对3d4s(1D2)nf2D3/2系列,考虑偶极极化效应后的结果和仅考虑冻结实的结果比较接近,理论计算和实验测量的量子数亏损之差普遍在0.04左右.     

Study of phase transformation dynamics in Na1/2Bi1/2TiO3 by Mandelstam-Brillouin scattering

The results of the study of Mandelstam-Brillouin light scattering in single-crystal Na_1/2Bi_1/2TiO₃ within a broad temperature interval covering successively the cubic, tetragonal, and rhombohedral phases are reported. Measurements conducted within the range 820–300 K have revealed quasi-elastic scattering and distortion of the phonon spectra in shape, which suggests possible coupling between the low-frequency transverse optical and acoustic modes. These two observed phenomena are believed to be closely interrelated.     

Estimating ground-state energies in supersymmetric quantum mechanics: (1) Broken case

For a class of the dynamically broken supersymmetric quantum-mechanical models proposed by Witten, we examine various methods of estimating the ground-state energy, including the instanton method developed by Salomonson and van Holten. We show that no existing method is entirely satisfactory, and develop a method using all stationary points of the Schrödinger potential (including those in the complex plane) in conjunction with the Rayleigh-Ritz variational method, thus combining perturbative and nonperturbative effects. Generalisations to more than one degree of freedom and to field theory are discussed.     

Structural first-order transformation in La2/3Ba1/3MnO3: ESR study

We have studied by the electron-spin resonance (ESR) and static magnetic field techniques, the La_2/3Ba_1/3MnO₃ perovskite, which was previously shown to exhibit a martensitic phase transformation in the vicinity of T_s∼200 K [Physical Review B 68, 054109 (2003)], leading to its structural phase-segregated state. Resonant absorptions reveal that in the temperature interval from 100 K to 340 K the compound represents a mixture of two ferromagnetic phases possessing different magnetizations, in varying proportions depending on the temperature, and a small amount of a paramagnetic phase. The results agree well with the previous neutron diffraction study. Applied in the ESR experiments, magnetic fields (2–6 kOe) strongly affect the magnetization curves: even magnetic field as high as 700 Oe modifies the anomaly in the phase transformation region and removes the difference between the zero-field cooled and field-cooled magnetization curves, which implies that the difference in the magnetic susceptibility of the coexisting phases is small and the magnetic domain configuration can be easily changed.