Shoulder Structure Research Articles

Multifractal multiplicity distribution in and interactions from nonlinear Markov process

The multifractal negative binomial distribution derived from the nonlinear Markov process has been used to explain the multiplicity distributions in high-energy and interactions. The analysis aims at explaining the shoulder structure and high-multiplicity tail of these distributions and determining the strength of influence of nonlinearity in the restricted phase-space intervals which is related to the degree of multifractality.

Seeing phi mesons through dileptons

Dilepton spectra from the decay of phi mesons produced in heavy-ion collisions at SIS/GSI energies (∼ 2 GeV/nucleon) are studied in the relativistic transport model. We include phi mesons produced from baryon-baryon, pion-baryon, and kaon-antikaon collisions. The cross sections for the first two processes are obtained from a one-boson-exchange model, while that for the last process is taken to be of the Breit-Wigner form through the phi meson resonance. For dileptons with invariant mass near the phi meson peak we also include contributions from neutron-proton bremsstrahlung, pion-pion annihilation, and the decay of rho and omega mesons produced in baryon-baryon and meson-baryon collisions. Effects due to medium modifications of the kaon and vector (rho, omega and phi) meson properties are investigated. We find that the kaon medium effects lead to a broadening of the dilepton spectrum as a result of the increase of the phi meson decay width. Furthermore, the dropping of the phi meson mass in nuclear medium leads to a shoulder structure in the dilepton spectrum besides the main peak at the bare phi meson mass. The experimental measurement of the dilepton spectra from heavy-ion collisions is expected to provide useful information about the phi meson properties in dense matter.

Correlations and multiplicity distributions in high energy collisions

In celebrating the 25 th anniversary of QCD, the theory of strong interactions, we focus our attention on the still standing problems of its non-perturbative sector using the advanced statistical methods and observables currently employed in multiparticle dynamics. In this paper we illustrate how H q oscillations and shoulder structure in e + e − annihilation are explained in terms of the superposition of 2- and 3-jet samples of events. Similar effects are also seen in the 2-jet sample of events and interpreted as the superposition of jets of different flavours. The elementary substructure in the two cases turns out to be a negative binomial distribution. It is proposed to interpret in the same way also H q oscillations and shoulder structure observed in hadron-hadron collisions.

Inverse photoemission and soft X-ray emission spectra of Al [sbnd]Ni [sbnd]Co decagonal single quasicyrstal

Inverse photoemission spectra (IPES) of a decagonal single quasicyrstal Al 72Ni 12Co 16 have been measured for various incident electron energies E i together with its Al L 2,3 soft X-ray emission spectra (SXES). Both IPES and SXES show low intensity near the photon energy corresponding to the Fermi level, which is consistent with an opening of a pseudo-gap across the Fermi level. The IPES shows no strong resonance enhancement, suggesting apparently small density of the transition metal d states above the Fermi level. However, constant final state spectra of the inverse photoemission reveal faint humps around E i = 62 and 76 eV, which might indicate resonances due to the Co and Ni3 d-derived states, respectively. A shoulder structure at the low photon energy side of the main band in the Al L 2,3 SXES becomes prominant for the lower incident electron energy and is tentatively ascribed to the Ni3 p emission band.

X-ray photoemission study of Pr/noble metals (Ag, Au) and Pr/transition metals (Ni, Pd)

The electronic properties of the interfaces ofPr/Ag, Au, Ni, and Pd were studied by X-ray photoemission spectroscopy. Pr thin films with coverage between 0.2 and 6.4 ML were prepared by evaporation onto the metal substrates at room temperature. Core level shifts of the substrates and Pr as well as changes of Pr 3d spectral shape were observed as a function of Pr coverage, indicating that the formation of intermixing alloys occurs at the interfaces. In Pr3d 5/2 spectra at low coverage, a high energy satellite with shoulder structure is interpreted as an f 1 final-state peak. This suggests that the tetravalent Pr state exists at very low Pr coverage.

Selective MBE growth of GaAs wire and dot structures using atomic hydrogens and their electronic properties

The selective growth of GaAs wire and dot structures by molecular beam epitaxy in the presence of atomic hydrogen was studied on a GaAs substrate with stripe and window shaped SiN x mask patterns. It was found that 20 nm ridges were successfully formed on long stripe patterns but the ridge width increased substantially when grown on short stripes of less than several μm. This is ascribed to the longitudinal migration of Ga flowing from the two ends of a stripe to its central zone. The incorporation of Si dopants into a 0.3 μm-wide wire was achieved. Negative magnetoresistance and conductance fluctuations indicative of the one-dimensional nature of electrons were observed. On a 2 x 2 μm square window pattern, a pyramidal structure with two-fold symmetry was formed, on which a GaAs dot with the lateral dimension of 100 nm was grown. Photoluminescence (PL) spectra from this dot exhibited a shoulder structure 15 meV, suggesting the filling of several discrete levels and the slow relaxation of carriers.

Common origin of the shoulder in multiplicity distributions and of oscillations in the factorial cumulants to factorial moments ratio

The shoulder structure of charged particles multiplicity distributions (MD's) in full phase space in e + e − annihilation at the Z 0 peak and the quasi-oscillatory behavior of the ratio of factorial cumulants over factorial moments, H q , as a function of the order q, are quantitatively reproduced within a simple parametrization of the MD in terms of a weighted superposition of two Negative Binomial Distributions, associated to two- and multi-jet production, i.e., to hard gluons radiation.

Size dependence of lateral quantum-confinement effects of the optical response in In0.53Ga0.47As/InP quantum wires.

The size dependence of various aspects of quantum-confinement effects in ${\mathrm{In}}_{0.53}$${\mathrm{Ga}}_{0.47}$As/InP quantum wires was quantitatively examined through photoluminescence experiments with and without magnetic field, along with theoretical calculation. The wires were fabricated by combining electron-beam lithography and reverse-mesa wet etching, thus enabling us to easily control the lateral size independently of the vertical size. Photoluminescence experiments showed distinct peak shifts with changes in the lateral size and showed a shoulder structure that is attributed to laterally quantized second subbands. The energy shift of both levels is explained by a detailed theoretical calculation that incorporates conduction-band nonparabolicity, valence-band coupling, and excitonic correction. The lateral quantum confinement is also demonstrated by the magnetic-field effect on the luminescence spectrum, in which we can distinguish the lateral quantum effects from other factors. As magnetic-field strength increases, a transition from quantum-confined subbands to Landau subbands was clearly observed for first and second subbands. At high excitation levels, the quenching of higher Landau levels was observed. In-plane and perpendicular-to-plane anisotropy of polarization in luminescence was also investigated and the size dependence of this anisotropy in both directions is largely explained by the calculated lateral confinement effect of the optical-transition matrix elements. The phenomenon observed for narrower wires, however, cannot be explained by our theory and is thought to be due to wave-function localization.

Photoelectron spectra of a higher fullerene compound C 82 and its potassium complex

Photoelectron spectra of C 82, which has been reported to contain metal atoms inside, are measured with a synchroton radiation light source. The spectra resemble those of C 84. The spectra begin at 1.1 5 eV below the Fermi level (E f). The first band consists of two peaks located at 2.2 eV and 3.3 eV accompanied by a slight shoulder structure at the lower binding energy side. This shoulder is not observed in C 84. The intensity of the two peaks of the first band oscillates with the incident photon energy change, as are observed in C 60, C 70 and C 84. The second band locates between 4 and 6.2 eV with a peak at 5.3 eV and a shoulder at the lower binding energy side. The third band locates between 6.2 and 9 eV and consists of a peak at 7.8 eV and a distinct shoulder at 6.5 eV. Potassium dosing brings a new band between the E f and the first band and its intensity grows as the potassium dosage increases. The spectral onset approaches toward the E f in accordance with increase of potassium dosage but it does not cross the E f, which indicates a semiconductive nature of K xC 82.

Structural Studies of Some High Tc Superconducting Oxides through XANES and XPS Techniques

Some structural investigations have been carried out in case of YBa2Cu3O7-x and Bi2.2Ca2.1Sr0.7Cu2Oy using XANES as a probe and Cu2O and CuO as reference compounds. While such studies have been performed in terms of the pre-edge structure, principal absorption maximum and shoulder structure beyond the principal absorption maximum, complementary information obtained from 2p core-level XPS of Cu has been used to ascertain charge transfer from oxygen 2p states to vacant 3d states of copper.

Magneto-tunneling in the n-type-GaAs/AlGaAs wide-well double barrier structure under transverse high magnetic fields

The magneto-tunneling effect was studied in the n-GaAs/Al 0.4Ga 0.6As double barrier structure with a wide quantum well under high magnetic fields up to 35T parallel to the layers. In addition to the oscillatory tunneling structures, we found a shoulder structure in the d I/d V characteristics and a perfect quenching of the tunneling current below the threshold voltage at high magnetic fields. The calculations taking account of the finite barrier height suggest that the shoulder structure corresponds to the onset of the tunneling into the mixed states extending over the well and the collector, and that the current quenching is caused by the absence of the well state into which emitter electrons can tunnel.

Multiplicity distributions in high energy collisions

We discuss the important phases in the evolution of our understanding of multiplicity distributions in high energy collisions with particular emphasis to intermittent behavior and shoulder structure problem.

Multiplicity distributions in high energy collisions

We discuss the important phases in the evolution of our understanding of multiplicity distributions in high energy collisions with particular emphasis to intermittent behavior and shoulder structure problem.

Theory of Cu 2 p X-ray emission spectroscopy in high-T c superconductors

We investigate theoretically Cu 2 p-XES for La 2CuO 4 and CuO on the basis of the formula of the second order optical process with the impurity Anderson model. According to Cu 2 p-XES experiments so far made, a shoulder structure appears on the high energy side of the main peak in La 2CuO 4 and also in high-T c superconductors, but it is absent in CuO. It is shown that the appearance of the shoulder structure originates from the stronger hybridization for the a lg symmetry states in La 2CuO 4 than in CuO due to the existence of the apical oxygen.

Theory of Cu 2pX-Ray Emission Spectroscopyin CuO and La2CuO4

Soft X-ray emission spectroscopy due to the Cu 3 d →2 p electronic transition (Cu 2 p -XES) is one of the powerful tools for investigating the local nature of the Cu 3 d state in high- T c superconductors. We theoretically investigate Cu 2 p -XES for CuO and La 2 CuO 4 based upon the impurity Anderson model and the formula of the second order optical process. Justification for this model is given by that available experimental data of Cu 2 p -XES, 2 p -XPS, 2 p -XAS and 3 d -XPS are satisfactorily reproduced in a unified way. According to Cu 2 p -XES experiments so far made, a shoulder structure appears on the high energy side of the main peak in La 2 CuO 4 and also in high- T c superconductors, but it is absent in CuO. It is shown that the appearance of the shoulder structure originates from the stronger hybridization for the a 1 g symmetry states in La 2 CuO 4 than in CuO due to the existence of the apical oxygen.

Charged particle multiplicity distributions in restricted rapidity intervals inZ 0 hadronic decays

The multiplicity distributions of charged particles in restricted rapidity intervals inZ 0 hadronic decays measured by the DELPHI detector are presented. The data reveal a shoulder structure, best visible for intervals of intermediate size, i.e. for rapidity limits around ±1.5. The whole set of distributions including the shoulder structure is reproduced by the Lund Parton Shower model. The structure is found to be due to important contributions from 3-and 4-jet events with a hard gluon jet. A different model, based on the concept of independently produced groups of particles, “clans”, fluctuating both in number per event and particle content per clan, has also been used to analyse the present data. The results show that for each interval of rapidity the average number of clans per event is approximately the same as at lower energies.

A BRIEF REVIEW OF RECENT STUDIES OF C, Si AND Ge METALLIC LIQUIDS

A brief review of recent studies of C, Si and Ge metallic liquids is presented. We compare results from density functional calculations using (a) a model of diffusively free ions as in a simple metal or plasma (b) Car-Parrinello type MD-simulations which involve many center interactions and (c) Stillinger-Weber type models which start from the Lennard-Jones covalent-bond prototype. The simple metallic model using one-parameter pseudopotentials and pair-potentials lead to structure factors S(k) in good agreement with experiment, with Car-Parrinello MD calculations and those of Stillinger and Weber. The shoulder structure in the S(k) is explained in the metallic model in terms of competing minima in the pair-potential. The metallic model predicts that l-Carbon has a single sp-band, is highly conducting and strongly compressible, with a broad peak in S(k) located near the ‘hump’ in the S(k) of l-Si. The structure factors and pair correlation functions were calculated using the modified hyper-netted chain equation.

XAFS study of nasicon-related compounds, Na 3Zr 0.5Co 0.5FeP 3O 12 and Na 3Zr 0.5Fe(II) 0.5Fe(III)P 3O 12

The XAFS analyses of the Na + ion conducting Na 3Zr 0.5Co 0.5FeP 3O 12 (NCFZP) and mixed-conducting Na 3Zr 0.5Fe(II) 0.5Fe(III)P 3O 12 (NFZP) are performed at both 60 K and 300 K. The XANES spectra of NCFZP and NFZP at the Zr K-edge show a similar structure to that of the host material NaZr 2P 3O 12 (NZP). The Fe K-edge XANES spectrum of NFZP is similar to that of NCFZP, but it contains a parasitic shoulder structure at lower energy. The Zr-O distance of NCFZP and NFZP does not vary from that of NZP, while their Zr-Na distance is significantly shorter than that of NZP. The population of the Na + ion around the doped ions (Co 2+, Fe 2+ and Fe 3+) in NCFZP and NFZP is increased preferentially as compared with that around the Zr 4+ ion, and distances between the doped ions and Na + are rather shorter than the Zr 4+-Na + distance of NZP.

Excitation spectra of the degenerate Anderson model with finite f-f Coulomb interaction

Spectral densities of local single particle, magnetic and charge excitations are calculated for the impurity Anderson model based on the renormalization group approach. Calculations are made for various magnitudes of the f-f Coulomb interaction. The role of the multiplet splitting and of the so-called negative U interaction is also examined. The width of the peak at the Fermi level in the single particle spectrum has always a scale comparable to that of the magnetic excitation and is never larger than the hybridization width. The broad band-like peak in BIS of U-compounds is interpreted by a broad shoulder structure which appears when the f-f interaction is not small and the f-electron number is intermediate and larger than 1.

Optical absorption of MgGa 2Se 4:Ni 2+ single crystals

Optical absorption of MgGa 2Se 4:Ni 2+ single crystals have been investigated in the visible and near-infrared region. We observed optical absorption peaks at 4597, 5807, 8779, 10416, 11876 and 11936 cm −1 due to nickel impurity and at 9088 cm −1 due to phonon of MgGa 2Se 4. The three absorption bands at 4597, 8779 and 11876 cm −1 among them are attributed to the crystal field transitions between the ground state 3 T 1( F) and the excited states 3 T 2( F), 3 A 2( F) and 3 T 1( P) of Ni 2+ ion with T d symmetry of MgGa 2Se 4 host. On the other hand, the two absorption bands at 5807 and 10416 cm −1 are assigned to the charge-transfer transitions of Ni 3+ + hv → Ni 2+( 3T 1(F)) + hole and Ni 3+ + hv → Ni 2+ ( 3T 2(F)) + hole , respectively. The shoulder structure at 11936 cm −1 is also ascribed to the charge-transfer transition of Ni 2+ ( 3T 1(F)) + hv → Ni 3+ + electron. From the optical absorption results, the energy levels of Ni 2+ ion are deduced and illustrated schematically relative to the band edges of MgGa 2Se 4.