Far-infrared two-photon intraband transitions in n-InSb

Two-photon cyclotron resonance and two-photon shallow donor transitions have been excited by a high power pulsed D₂O laser emitting λ = 119 μm and 66 μm laser lines at the same time. Transitions involving the absorption of two 119 μm photons or simultaneously one 119 μm and one 66 μm photon were observed. Two-photon selection rules are discussed by a rigorous treatment of the symmetry of the free electron Hamiltonian.     

Field-induced spin-flip and spin-flip transitions in PrGa2

A detailed neutron diffraction study of a single crystal of hexagonal PrGa₂ under an applied field is presented. The field is applied along the easy [100] direction of the hexagonal plane. The compound exhibits several field-induced magnetic structures and, in particular, an uncompensated long period commensurate antiphase structure defined by the propagation vector (4/27, 4/27, 0) at zero field and below T_t = 3.5 K. Concerning the intermediate magnetic structures below T_t, two types of magnetic phase transitions are observed: a spin-flip transition where one moment per magnetic cell turns over, and a spin-slip transition from the low field commensurate propagation vector (4/27, 4/27, 0) to another commensurate vector (1/7, 1/7, 0). Between T_t and T_N = 7.2 K, the structure becomes apmlitude-modulated with a propagation vector (0.148, 0.148, 0.023). Important and original magnetic domain effects are also observed due to the high degeneracy of the easy direction of the hexagonal plane in both T<T_t and T_t<T<T_N regions.     

Resonant neutrino spin-flip transitions in twisting magnetic fields

We examine here in detail the dynamics of neutrino spin-flip transitions in twisting magnetic fields. The properties of various resonant conversions induced by field rotation are considered. The suppression factors for solarv _eL due to spin-flip transitions in twisting magnetic fields are calculated, and possible implications for solar neutrino experiments are discussed.     

A note on spin-flip electric dipole transitions

Inelastic scattering 22MeV proton from²³⁸U has been studied. Angular distributions of the states of the rotational band have been measured. Coupled-channel analysis allows determination of the deformation parametersβ ₂,β ₄ andβ ₆. These values are somewhat in disagreement with other experimental results.     

Three-phonon assisted cyclotron harmonic transitions in the magnetophotoconductivity of n-InSb

The CO₂ laser-induced magnetophotoconductivity of n-InSb (10¹⁴ cm^-3) at liquid helium temperatures exhibits resonant structure which depends upon the photon energy and the magnetic field. The resonant peaks are explained on the basis of a simple model in which an electron absorbs a photon and emits successively three LO phonons.     

New intraband magneto-optical studies on n-InSb

A highly sensitive photoconductive technique has been used to provide the first direct evidence of emission of five optical phonons during the energy relaxation process of the photoexcited electrons induced by a CO₂ laser in n-InSb. The CO₂ laser-induced magnetophotoconductivity exhibits a number of very sharp resonances whose positions depend strongly upon photon energy. All observed transitions can be described with one single set of band parameters.     

Search for giant spin-flip transitions in 90Zr and 208Pb

We have searched for the giant magnetic dipole resonance in ⁹⁰Zr and an associated state in ²⁰⁸Pb. Among the experimental techniques employed in this search was the detection of inelastically scattered protons in coincidence with ground-state de-excitation γ-rays, No state in ⁹⁰Zr up to an excitation of 10.5 MeV or in ²⁰⁸Pb between 5.0 to 6.0 MeV was observed with the desired characteristics. In ⁹⁰Zr, heretofore unidentified levels at 5.51, 5.89 and 6.42 MeV were determined to have J^π = 1^?. In ²⁰⁸Pb J^π = 1^? states were observed at 5.29, 5.51 and 5.94 MeV. The implications of our observations are discussed.     

Role of spin-flip transitions in the anomalous Hall effect of FePt alloy

We carry out ab?initio calculations which demonstrate the importance of the non-spin-conserving part of the spin-orbit interaction for the intrinsic anomalous Hall conductivity of ordered FePt alloys. The impact of this interaction is strongly reduced if Pt is replaced by the lighter isoelectronic element Pd. An analysis of the interband transitions responsible for the anomalous velocity reveals that spin-flip transitions occur not only at avoided band crossings near the Fermi level, but also between well-separated pairs of bands with similar dispersions. We also predict a strong anisotropy in the anomalous Hall conductivity of FePt caused entirely by low-frequency spin-flip transitions.     

Multipole and spin-flip interband transitions in the electron energy loss of ferromagnetic Fe

Electron energy loss measurements have been carried out in the reflection mode from polycrystalline iron. The observed structures are interpreted as surface and bulk collective losses by observing their dependence on the primary electron energy and surface oxidation. Interband transitions in the range 2–30 eV are pinpointed and found to be in excellent agreement with previous optical results, except for a new strong transition around 10 eV, which is not found in optical experiments. This transition is tentatively identified with a dipole-forbidden process, which becomes allowed because of finite momentum transfer by the electrons.     

Optimum-non-linear optical mixing in n-InSb

The optimum conditions to obtain maximum output power of frequency w₃ = 2w₁ − w₂ from a sample of n-InSb have been discussed.     

New Photoelectronic investigations of the nonlinear optical properties of n-InSb

The nonlinear optical properties of n-InSb at liquid helium temperatures are shown to be strongly related to the electron population of the shallow donor impurity levels. Solutions of nonlinear coupled rate equations predict the observed resonant behavior of (1) the number of photoexcited electrons (determined directly from photo-Hall measurements) and (2) their resonant lifetime behavior at magnetic fields where two-photon interband transitions take place.     

Two-photon bound state-bound state transitions in a Coulomb field

Expressions are given for various two-photon transitions.     

Nonlinear oscillations and chaos in n-InSb

We present evidence for chaotic behavior in n-InSb. The Hall voltage exhibits a period-doubling route to chaos as the (non-ohmic) dc current is increased. The nonlinear oscillation and bifurcation processes are strongly influenced by irradiation with CO₂ laser radiation.     

Two-photon resonant photo-hall effect in n-InSb

Resonant two-photon structure is observed in the photo-Hall response of n-InSb at liquid helium temperatures. The number of two-phonon photo-excited carriers, directly determined from the photo-Hall effect, is seen to be proportional to the square of the incident laser intensity and to decay via a two-stage process. The low intensity and photo-excited carrier decay results are described using a three-level system involving the shallow donor impurity levels.     

Free and bound electron transitions to acceptors in indium phosphide

In epitaxial InP a new emission band at 1.3776 eV is identified as the free electron-acceptor transition. It is investigated in connection with the corresponding donor-acceptor pair band at 1.374 eV. This permits an individual determination of the acceptor and donor binding energies (48 ± 1 meV and 7.3 ± 0.6 meV respectively). A second new emission band at 1.396 eV is reported and discussed.