Instability of polarons and bipolarons in conducting polymers at various 3-d ordering types

Interchain electron hopping t_⊥ in conducting polymers with the small confinement parameter γ leads to the antiferromagnetic (AB) 3-d ordering of the dimerization pattern only at 2t²_γ >γΔ² (2Δ being the Peierls gap), otherwise the ferromagnetic (AA) one occurs. Polarons (Ps, υ = 1) and bipolarons (BPs, υ = 2) stability areas: t_⊥/Δ<t_c (υ,γ) are found in the phase plane “t_⊥ vs γ” with critical t_c being larger in the AB phase and for BPs. At the AA-AB transition interface, “deconfinement” of kink-solitons is possible. Photogeneration of Ps and BPs may proceed via metastable free states separated by the self-trapping barriers (STBs) which are also different in AA and AB (in the latter STBs exist even in 2-d systems) and are lower for BPs.     

Localization in a system of N coupled chains

The behaviour of a quantum particle moving in a system of N coupled chains parallel to each other and packed into a bundle is investigated in the presence of weak disorder. This system may be thought of as a model of an anisotropic thin wire. The dependence of the localization length r_loc on N and t_⊥ is studied (t_⊥ is the interchain exchange integral characterizing the strength of the interchain tunneling). For t_⊥ < t_c ≅ h/τ the localization length r_loc increases proportionally to lt_⊥/(t_τ −t_⊥) attaining a plateau value of the order of Nl (τ is the relaxation time and 1 the mean free path for elastic scattering). Such a behaviour may be called a transition from the Mott localization regime to the Thouless localization regime. It may be considered as a precursor of the insulator-metal transition (r_loc → ∞) occuring for t_⊥ → t_c in the quasi-1d system (N → ∞).     

Observation of πo mesons with large transverse momentum in high-energy proton-proton collisions

Invariant cross-sections are presented for the inclusive reaction p + p → π^o + anything, Measurements of large transverse momentum π^o's (2.5 GeV/c<p_⊥<9 GeV/c) were made near 90° at the CERN ISR at five centre-of-mass energies (√s = 23.5, 30.6, 44.8, 52.7 and 62.4 GeV. At large p_⊥, the invariant cross-sections are seem to vary with s and p_⊥, in good agreement with a fit of the form Ap_⊥^?nF(p_⊥/√s), with n≈8 and F(p_⊥/√s)≈exp(?26p_⊥/√s).     

Thermoreflectance of single crystal Gd

Thermoreflectance spectra for E∥c and E⊥c were measured on a Gd single crystal. The thermoconductance spectra, Δσ_∥ and Δσ_t], are very anisotropic. The strong interband edge at about 0.5 eV is shown to arise from a transition to or from the Fermi level for E⊥c. For E∥c additional effects occur.     

Measurement of proton proton elastic scattering in pure initial spin states at 11.75 GeV/c

The elastic cross section for proton proton scattering at 11.75 GeV/c was measured at the Argonne ZGS using a 50% polarized target. In the range p_⊥²=0.6 → 2.2 (GeV/c)² we obtained precise measurements of $\text{d}\text{σ}\text{d}\text{t(ij)}$ for the ? ?, and ? initial spin states perpendicular to the scattering plane. We confirmed that the asymmetry parameter, A, decreases with energy in the diffraction peak, but is approximately energy-independent at large p_⊥². We found that the spin correlation parameter c_nn acquires rather dramatic structure, and at large p_⊥² seems to grow with energy.     

Low-frequency dispersion of the effective transverse conductivity in inhomogeneous media in strong magnetic field

On crystalline silicon specimens with a nonuniform carrier concentration distribution produced by an optical method, a dispersion of the effective transverse conductivity σ _⊥ ^eff (ω) is observed near the frequency ω≈ω_c=τ _⊥ ^?1 ≡ε/4πσ _⊥ ^eff . At ω<ω_c, an anomalous transverse effective conductivity is observed: σ _⊥ ^eff (ω) is greater than the transverse conductivity of a homogeneous specimen σ _⊥ ^h (ω) (in the frequency range studied in the experiment σ _⊥ ^h (ω) = const). Near ω≈ω_c, the conductivity σ _⊥ ^eff decreases, and, at ω>ω_c it coincides with σ _⊥ ^h .     

Effect of the spin-orbit interaction of Ni2+ ions with a triplet orbital ground state on the magnetostriction of NiFe0.5Cr1.5O4 ferrite

The magnetization σ and the longitudinal (λ_∥) and transverse (λ_⊥) magnetostrictions of the NiFe_0.5Cr_1.5O₄ ferrite containing the tetrahedral ions Ni²⁺ with the triplet orbital ground state have been investigated for the first time at a temperature of 4.2 K in fields up to 55 kOe. It is revealed that the NiFe_0.5Cr_1.5O₄ ferrite exhibits an anomalously large magnetic anisotropy (H _c=12.5 kOe) and magnetostrictions (λ_∥≈?870×10^?6 and λ_⊥≈800×10^?6). In strong fields, the magnetostrictions λ_∥ and λ_⊥ are found to be anisotropic in character; i.e., the susceptibility Δλ_∥p and Δλ_⊥p. The conclusion is drawn that the studied compound is characterized by two paraprocesses: one paraprocess in the B sublattice has an exchange nature, and the second process in the A sublattice is due to the spin-orbit interaction of Ni _A ²⁺ ions.     

Einfluß der Bestrahlung mit hochenergetischen Sauerstoffionen auf die kritische Stromdichte supraleitender Nb3Sn-Schichten

Nb₃Sn diffusion layers were irradiated with 24 MeV oxygen ions at fluences from 3.2×10¹³ up to 1.6×10¹⁵ cm^?2. The enhancement of the superconducting critical current density Δj _c has been measured as a function of fluence and of the external magnetic fieldH _a(j _c⊥H _a). The thermal annealing treatment of the defects concerning thej _c and induced by irradiation, has been investigated in the temperature region from 200 to 800 °C. The results are compared with the measurements of irradiation of Nb₃Sn with protons and deuterons. The measured data are discussed in connection with size of defects, cluster distance, fluxline distance and pinning-force.     

Spectra of negative particles and photons in collisions of p−W and16O−W at 200 GeV/u

p _⊥ spectra of negative particles were measured for p?W and¹⁶O?W collisions at 200 GeV/u in the rapidity range 0.9<y<1.9. Within the systematic errors of 20% the spectra are identical in the range 0.05<p _⊥<2.0 GeV/c. The p?W and¹⁶O?W spectra exhibit an exponential shape forp _⊥ >250 MeV/c. This is consistent with previous p?A data, but there is a significant excess above this exponential at lowerp _⊥. Photon spectra were measured using a conversion method. Theirp _⊥ distribution agrees in shape with the sum of known hadronic γ-sources.     

Measurement of the tensor analyzing power A yy in the inelastic scattering of 4.5-GeV/c deuterons on beryllium at an angle of 80 mrad

The tensor analyzing power A _yy and the vector analyzing power A _y for the inelastic scattering of 4.5-GeV/c deuterons on beryllium nuclei at angle of about 80 mrad are measured in the vicinity of baryon-resonance excitation. These new data, presented as a function of t, comply well with the results of previous 4.5-, 5.5-, and 9-GeV/c measurements at zero angle in overlapping regions of t; all available data are described by a unified dependence on |t| upto about 0.9 (GeV/c)². The experimental results are compared with the results of calculations performed within the multiple-scattering model and the model involving omega-meson exchange in the t channel.     

Magnetophonon oscilation of thermoelectric power in the conduction band of tellurium

At about 200K where the Hall coefficient of p-Te reverses its sign, magnetophonon oscillation of electron in the conduction band was observed for the first time in H6c and H⊥c. It was attained by measuring the second derivative of the longitudinal magneto-Seebeck coefficient (?²α₆/?H²). It is found to be explained fairly well by a simple parabolic band model even for H6c. Effective mass values of the conduction band at 200K are deduced on an interpretation; $\text{m}{}^1{}_{\mathrm{\perp }}\text{=0.160m}{}_0$ and $\text{m}{}^1{}_6\text{= 0.072m}{}_0$. Rather large contribution of electron in ?²α₆/?H² may be due to the enhanced electron diffusion in a transition region from p-type to intrinsic as reported recently in p-InSb. This interpretation is supported also by the oscillation of longitudinal magnetoresistance (?²?₆/?H²) which was observed for H6c.     

Gleichzeitige Messung von Hyperfeinstruktur,Starkeffekt und Zeemaneffekt des85Rb19F mit einer Molekülstrahl-Resonanzapparatur

A molecular beam resonance apparatus with electric quadrupole lenses asA- andB-fields and with superimposed parallel electric and magnetic transition-fields was used. Molecules in different rotational statesJ, m _J are separated by theA-field. Spectra of molecules in different vibrational states are resolved by their different Starkeffect energies. By this means the following electric and magnetic properties of the molecule could be measured in the rotational stateJ=1 and vibrational statesv=0 and 1: The magnetic and electric dipole moment of the molecule, the scalar and the tensor nuclear dipole — dipole interactiond _s andd _T, the nuclear spinrotational interactionc _F andc _Rb, the nuclear quadrupole interactioneqQ, the nuclear magnetic moment μ_Rb, the anisotropy of the diamagnetic susceptibility ξ_⊥?ξ_∥, the anisotropy of the diamagnetic shielding of the external field by the electrons at the position of the nuclei σ_⊥?σ_∥. Using these quantities it was possible to calculate the quadrupole moment and a weighted quadrupole moment of the electronic charge distribution. The results are: (J=1,v=0) μ_el=8,5464 (17) debμ _J/J=?29,79(2)x10^?6 μ _B d _s/h=0,36(23) kHzd _T/h=0,69(22)kHzc _F/h=10,42(70) kHzc _Rb/h=0,479 (48) kHz.eqQ _Rb/h=?70,3410(26) MHzμ(1?σ_S)Rb=1,3474(5) μ_k (ξ⊥-ξ _∥)=12(6)×10^?30 erg/Gauß² (σ_⊥-σ∥)_Rb=?3,8(2,1)×10^?4 (σ⊥-σ _∥)_F=?2,6(3)×10^?4     

Production of large p⊥ single particles and multiparticle systems (JETS) in K−p interactions at 110 GeV/c

Differential cross sections of single particles and multiparticle systems produced in K^?p interactions at 110 GeV/c are presented. At large values of transverse momentum (p_⊥) we find the multiparticle cross section to be an order of magnitude larger than that for single particles. This and other features of our data are consistent with results obtained at 200 GeV/c, that have been interpreted as evidence of a new dynamical mechanism in hadron-hadron interactions. However, similar features are observed in a K^?p experiment at 16 GeV/c.     

Photoproduction of Φ-mesons at small t-values

The reaction γ + p → Φ + p has been measured using a spark chamber spectrometer and a tagged photon beam in the energy range from 4.6 to 6.7 GeV. Approximately 3500 photoproduced elastic Φ-events have been collected in the t-range between t_min and t = ?0.4 (GeV/c)². Cross sections and t-distributions are presented.     

Inclusive single-particle distributions in π±p reactions at 8 and 16 GeV/c

Invariant single-particle cross sections for pion and proton production in π^±p interactions at 8 and 16 GeV/c are presented in terms of integrated distributions as functions of x, reduced rapidity ζ and p_⊥², and also in terms of double differential cross sections E d²σ/(dx dp_⊥²) and dζ dp_⊥²). A comparison of π^± and π^? induced reactions is made and the energy dependence is discussed. It is shown that the single-particle structure function cannot be factorized in its dependece on transverse and longitudinal momentum. For the beam-unlike pion, there is an indication for factorizability in terms of rapidity and transverse momentum in a small central region.     

Transverse-momentum dependence of J/Ψ production in nuclear collisions

The suppression of J/Ψ production at transverse moment p_⊥ < 2 GeV/c in central ¹⁶O+²³⁸U→Ψ+X at 200 A GeV has been interpreted as a possible signature of quark-gluon plasma formation. We show, however, that the observed p_⊥ dependence is consistent with extrapolations from p+A→Ψ+X data, and that quasielastic initial-state parton scattering together with final-state inelastic hadronic reactions may explain the preliminary data.     

Measurement of Large-angle πp elastic scattering at 5 GeV/c

The differential cross-section for 5 GeV/cπ⁺p and π⁻p elastic scattering have been measured in the c.m. angular region 27° < θ_cm < 130° corresponding to 0.5 < |t| < 7.8 (GeV/c)². Dips are observed in both reactions at −t = 2.8 and 4.8 (GeV/c)² where the cross-sections are approximately 0.1 μb/(GeV/c)².     

Transverse momentum of hadrons produced in ν and ν interactions on an isoscalar target in BEBC

The average transverse momentum squared, 〈p_⊥²〉, of hadrons is studied as a function of W² and of Q² for ν and $\text{ν}$ interactions on an isoscalar target. An increase of 〈p_⊥²〉 with W² is observed for the hadrons emitted forward in the hadronic c.m.s. The p_⊥ dependence of the fragmentation function is found to factorise from the structure function at fixed W, but does not factorise at fixed Q². Unlike the case of forward-going particles, the 〈p_⊥²〉 of hadrons going backward in the c.m.s. shows no strong dependence on W².     

Head-on and head-off collisions of discrete breathers in two-dimensional anharmonic crystal lattices

The ground-state phase diagram of the extended Falicov-Kimball model with f-f electron hopping is studied numerically in the one-dimensional case. To identify the nature of ground states three complementary numerical methods are used, and namely, (i) the small-cluster exact-diagonalization method, (ii) the density-matrix-renormalization-group method (DMRG) and (iii) an approximate, but very accurate, numerical method based on the reduction of the Hilbert space. It is found that the physics of the Falicov-Kimball model found for the zero value of the f-electron hopping integral t _f (including the existence of the devil’s staircase structure) persists also at finite values of t _f . The critical values of t ^c _f below which the physics of the Falicov-Kimball model dominates are calculated numerically and it is shown that they depend very strongly on the f-electron concentration n _f and only very weakly on the Coulomb interaction. In particular, we have found that for strong Coulomb interactions the value of t ^c _f rapidly increases from t ^c _f ~ 0.003 found for n _f = 1 / 4 up to relatively large t ^c _f ~ 0.4 found for n _f near the half-filled band case n _f = 1 / 2. In addition, the complete picture of valence transitions is presented for non-zero t _f and strong Coulomb interactions.