Sudden interchannel interaction in the Tl 6p ionization above the 5d threshold

The linear magnetic dichroism in the angular distribution of Tl 5d and 6p photoelectrons and their dynamical spin polarization have been measured between hnu = 30 and 50 eV. In contrast to the Xe 5p photoionization at the 4d threshold, our results show that above the Tl 5d threshold strong interchannel coupling effects induce a sudden increase in the asymptotic phase difference of the s and d waves for the Tl 6p ionization. This shows that the valence excitation is different for resonant (Xe 4d) and nonresonant (Tl 5d) excitation from subvalence shells.     

Electron-phonon coupling and its evidence in the photoemission spectra of lead

We present a detailed study of the influence of strong electron-phonon coupling on the photoemission spectra of lead. Representing the strong-coupling regime of superconductivity, the spectra of lead show characteristic features that demonstrate the correspondence of physical properties in the normal and the superconducting state, as predicted by the Eliashberg theory. These features appear on an energy scale of a few meV and are accessible for photoemission only by using modern spectrometers with high-resolution in energy and angle.     

Determination of the hole lifetime from photoemission: Ti 3d states in TiTe2

The electron hole spectral width Gamma(h) of Ti 3d states in layered TiTe2 and the inverse lifetime V(i) of the photoelectron final states are determined from experiment within the one-step theory of photoemission. The condition for the possibility of separating the effects of Gamma(h) and V(i) is a strongly non-free-electron character of the final states. The resulting drastic changes of the line shape with photon energy are experimentally observed and explained by an ab initio theory. A nonmonotonic dependence of V(i) on the final-state energy is observed; it is shown to reveal the real space structure of the complex electron self-energy.     

Two quasi-particle levels in136Ba and the decay of136Cs

The decay of 13-day¹³⁶Cs has been studied using high-resolution Ge(Li) detectors. Several low-intensity gamma rays were observed for the first time. New levels have been deduced in¹³⁶Ba at energies of 2356.7 and 2372.7 keV.     

Spin-orbit coupling enhancement of 3d ions in metals

The interactions between localised 3d and itinerant electrons due to the Coulomb and exchange potential are shown to be responsible for the increase in magnitude of ionic spin-orbit coupling.     

Nuclear quadrupole interaction at133Ba (EC)133Cs in Eu1Ba2Cu3O7−°

We studied the nuclear quadrupole interaction (NQI) at¹³³Ba(EC)¹³³Cs in Eu₁Ba₂Cu₃O_7–6 by time differential perturbed angular correlation between 11 K and 300 K. No anomalies in the NQI parameters around T_c were detected. All Ba sites appear to be identical and the precession frequency is ω=80(2) Mrad/s (assuming axial symmetry), independent of temperature.     

Decay of the134Cs isomers and the levels of134Xe,134Cs,and134Ba

A precision study of the decay of¹³⁴Cs ^g and¹³⁴Cs ^m has been made, using ordinary Ge(Li) spectrometers and ā Compton-suppression spectrometer. The logft value of the second forbidden nonuniqueβ-decay to¹³⁴Xe has been measured to be 13.0±0.2. TheM4γ-ray transition in¹³⁴Cs^m(8^?) decay has been measured to haveα _K= 73±7 and a hindrance of 7.0 over the Moskowski estimate. This is discussed in terms of the level configurations and the analogous transition in¹³³Xe. A new intensity limit of 2×10^?6 has been set for the zero-phonon transition between the 4⁺ and 2⁺ members of the two-phonon triplet. This leads to an upper limit forB(E2)_4→2′, greater than 905. This and the more preciseγ-ray intensity values are discussed in relation to presently available nuclear models.     

Relativistic and interchannel coupling effects in photoionization angular distributions by synchrotron spectrocopy of laser cooled atoms

We investigate the angular distribution of photoionization fragments at low photon energies (12-40 eV) in an open shell atom, by synchrotron radiation recoil ion momentum spectroscopy in a laser cooled and trapped sample. For cesium atoms, for which relativistic effects play an important role and the ion recoil is relatively small, we could determine large and rapid changes of the asymmetry parameter beta from two, observed for s electrons outside resonances and far from the Cooper minimum. They can be explained by relativistic effects and interchannel coupling arising from final state configuration mixing.     

Hyperfine-structure investigation in the 6s5d configuration of135Ba and137Ba

The hyperfine structure of the metastable states of the 6s5d configuration of¹³⁵Ba and¹³⁷Ba has been studied by the atomic-beam magnetic resonance (ABMR) method. The metastable barium states were populated in a plasma-discharge inside the atomic-beam oven. The atoms emerging from the ABMR-apparatus were detected by the use of a dyelaser. Compared to conventional methods this technique has the advantage of being state selective. The following magnetic dipole and electric quadrupole interaction constantsa andb have been obtained:¹³⁷Ba:a(³ D ₁)=?520.536 (3) MHzb(³ D ₁)=17.890 (3) MHza(³D₂=415.928 (3) MHzb(³D₂)=25.899 (13) MHza(³D₃)=456.559 (4) MHzb ³D₃=47.390 (16) MHz¹³⁵Ba:a ³ D ₁=?465.166 (4) MHzb(³D₁)=11.642 (4) MHza(³D₂)=371.736(4) MHzb ³ D ₂=16.745 (14) MHza(³D₃)=408.038 (6) MHzb(³D₃)=30.801 (24) MHz Using these constants and the earlier known ones for the¹ D ₂ state the hyperfine structure for the 6s5d configuration has been analyzed with an effective hyperfine hamiltonian. Hyperfine parameters obtained from the analysis have been compared with theoretical values calculated with relativistic self-consistent-field (SCF) wavefunctions. The quadrupole moments have been evaluated with the following result Q(¹³⁵Ba) =0.20(3)b and Q(¹³⁷Ba) = 0.34(4)b uncorrected for the quadrupole shielding.     

Surface photoemission in the 4d band from polycrystalline silver surfaces

Surface induced local d-band states in the upper 4d band between ～ 4 and ～ 5.2 eV below E_Fermi have been identified for polycrystalline silver films in photoemission experiments using synchroton radiation. A thin over-coat (10 å) by an Al film leads to a depression of these surface induced local states whereas a change from s- to p-polarized excitation leads to an enhancement. Deposition of additional silver (～ 3 Å) at 120 K induces additional emission 4.2 eV below E_F with a FWHM of only ～ 0.4 eV.     

In situ photoemission study of the contact formation of (Ba,Sr)TiO3 with Cu and Au

The contact formation of (Ba,Sr)TiO₃ thin films and SrTiO₃ single crystals with Cu and Au have been studied using X-ray and ultraviolet photoelectron spectroscopy with in situ sample preparation. During metal deposition a partial reduction of the substrate occurs. The Fermi level at the interface is found to be close to the conduction band minimum, indicating small Schottky barrier heights (< 0.2 eV).     

Oscillations in the threshold photoemission spectra of GaN(0001) with submonolayer Cs coverages

It is found that Cs adsorption on the n-type GaN(0001) surface generates an unusual change in the electronic properties of the surface and the near-surface space-charge layer, which leads to the appearance of photoelectron emission upon excitation in the transparent region of GaN. It is established that the photoemission is due to the formation of quasimetallic states induced by Cs adsorption in the band-bending region near the surface. The behavior of the photoemission threshold upon excitation by s-polarized light is studied as a function of the Cs coverage. It is found that the minimum value of the threshold corresponds to ～1.4 eV at a concentration of Cs atoms of ～4.5×10¹⁴ atom/cm² in the submonolayer coverage. A new effect is revealed, namely, the appearance of oscillations in the spectral curves of threshold photoemission. A model is proposed for photocurrent oscillations that takes into account the formation of quasimetallic states in the near-surface layer of GaN band bending and the occurrence of interference in the GaN slab upon light irradiation in the transparent region.     

Determination of the 5d6p 3F4-5d2 3F transition probabilities of Ba I

Whether the transitions between 6s5d ³D and 5d6p ³F can be used for laser cooling of barium heavily depends upon the transition probabilities of 5d6p ³F-5d^{2 3}F. Taking the transition 6s5d ³D₃-5d6p ³F⁴ as a scale, the leakage rate of 5d6p ³F₄-5d^{2 3}F was used to evaluate the transition probabilities. 706 nm laser pulses with different durations were applied to a barium atomic beam for 6s5d ³D₃-5d^{2 3}F₄ optical pumping, and the remaining percentages in 6s5d ³D₃ were measured. After exponential fitting, the transition probability of 5d6p ³F₄-5d^{2 3}F_3,4 was determined to be 2.1(4)×10⁴ s^?1, which is in agreement with theoretical calculations using the scaled Thomas-Fermi-Dirac method.     

124Ba Decay to the 55 124 Cs69 low-spin levels

The decay of¹²⁴Ba to the levels of odd-odd¹²⁴Cs has been studied with on-line mass-separated sources delivered at the Isocele facility. The energy level scheme has been established fromγ-ray singles,γ?γ?t coincidence ande?γ?t coincidence spectra. Spin and parity of several low-lying levels have been assigned on the basis of internal conversion coefficient measurements andβ-branchings. A completely new level pattern including approximately 50 levels and 180γ-rays is proposed for¹²⁴Cs. Several features of this level scheme are discussed and compared to those of neighbouring isotopes.     

Adsorbate enhanced Ti-3d photoemission from layered TiSe2 surfaces

Angle resolved photoelectron spectra of 1T-TiSe₂ single crystals $\text{(}\text{h}\text{?}\text{ω = 21.2}\text{eV}\text{)}$ have been investigated as a function of exposure to H₂O, CO, N₂ and O₂ at room temperature. A significant enhancement of the Ti-3d emission near the Fermi energy E_F is observed for H₂O and CO exposures of several kL. As compared to the clean surface this emission extends over the entire Brillouin zone. The results indicate that by H₂O and CO adsorption the lowest d-subband is pulled below E_F possibly by local band bending. Additional relaxation effects at the surface associated with changes in d-band matrix elements may occur. The intensity of the Se-4p derived valence band emission down to 7 eV below E_F remains essentially unchanged.     

Advanced multichannel laser systems with phase conjugation and interchannel phase locking by laser-gain-hologram long- and short-range coupling

Compact schemes of the phase-locked multichannel Nd:YAG laser system with the long- and shortrange coupling via the holographic gain gratings in the active elements are developed. The phase locking of various loop Nd:YAG lasers with an interference contrast of the laser channels of 0.50–0.87 and a single-mode lasing efficiency of up to 0.64% is experimentally demonstrated. The experimental results for the two- and three-channel laser systems are generalized on multichannel laser systems using the numerical simulation. It is demonstrated that the maximum number of the short-range-coupled laser channels can be increased owing to the leveling of the parameters of laser channels to a value that is greater than that the maximum number of the channels in the presence of the long-range coupling, which is limited by the damage threshold of the active element of the interchannel coupling.     

Self-organization of nanostructures on the n-GaN(0001) surface in the Cs and Ba adsorption

A regular self-organized 2D nanostructure of a new type of nanocombs has been created in situ in an ultrahigh vacuum on the n-GaN(0001) surface. The nanostructure is formed as a result of multilayer adsorptions of Cs and Ba. The structure is highly regular in the microrange, arranged in the form of combs 60–70 nm in diameter with a wall height of about 7 nm. It has been revealed that the nanostructure has a quasi-metallic conduction, a low work function of about 1.4 eV, and a high quantum yield of photoemission under light excitation in the GaN transparency region. A self-organization model is proposed, which implies the formation of a surface 2D longperiod incommensurate phase interacting with the superstructure of the Cs⁺ and Ba²⁺ ion clusters with allowance for the polaron compensation on the GaN surface.