Electric field-induced quasi-elastic inter-landau level scattering in the space-charge-limited magnetoconductivity of n+n−n+ InP structures

Magnetophonon resonance and quasi-elastic inter-Landau level scattering (QUILLS) are investigated in the transverse magnetoconductivity, σ_xx, of short (1 μm) n⁺n⁻n⁺ InP structures under conditions of space-charge-limited conduction. The damping of the magnetophonon resonance amplitudes at large E is also investigated. The electric field dependence of the QUILLS process in InP is in excellent agreement with a model that we have previously proposed to describe the process in n⁺nn⁺ GaAs layers. The observed form of the space-charge-limited current-voltage characteristics (I ∝ V²) is discussed in terms of the behaviour of electrons in short, lightly doped semiconductor layers under the influence of large, mutually perpendicular electric and magnetic fields.     

Single impurity-assisted tunnelling in sub-micron n+n−n+ multilayers

We have investigated n⁺n⁻n⁺ structures of GaAs in which the length of the active n⁻ region is comparable with the average donor separation. At low temperatures the resistance is independent of temperature and the magnetoresistance is large and anisotropic. These results are described by a simple quantitative model in which the low temperature conductivity is controlled by electrons tunnelling via shallow donors close to the mid-plane of the active layer.     

Surface effect on the reverse current of Al x Ga1−x Sbp−n structures

The effect of an invertedp-region along the free surface ofn-Al _x Ga_1−x Sb on the reverse current ofp−n structures from the given solid solution is analyzed. Expressions which describe “collection” of the inverted layer current on the cylindrical surface of ann-region are discussed. The contribution of the near-surface and bulk components to the reverse current ofp−n structures with a semi-infiniten-region is estimated. For structures with a two-layern-region of finite thickness we have calculated the dependence of the near-surface current on the voltage across thep−n structure, the thickness of then-region, and its composition and doping level. We have compared the calculated current-voltage characteristics with experiment using a Al_0.15Ga_0.85Sbp−n structure as an example. Tomsk State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 42, No. 1, pp. 34–40, January, 1999.     

Classical solutions ofℂP n−1 models and their generalizations

We discuss finite action solutions ofP ^n–1 models, of their Grassmannian generalizations and of a classical fermion — boson model based on the supersymmetric extension of theP ^n–1 model.Invited talk presented at the International Symposium Selected Topics in Quantum Field Theory and Mathematical Physics, Bechyn, Czechoslovakia, June 14–19, 1981.I would like to thank Dr. A. M. Din for his collaboration with me on all the topics discussed here. Also I would like to thank E. F. Corrigan, D. B. Fairlie, M. Günyadin, J. Lukierski, I. Singer, R. Stora and many others for discussions and constructive criticisms and Professor J. Niederle for his invitation to present this talk at the symposium and for hospitality in Czechoslovakia.     

Absence of continuous symmetry breaking in a one-dimensional n−2 model

For a one-dimensional array ofS ^N–1 spins (N 2) with isotropic pair interactions (and more general systems) with J(j–i) obeying sup_n[n^–1 ₁ ⁿ j ²|J(j)|]<, we prove that every equilibrium state is invariant under the natural action ofSO(N). In particular, there is no long-range order of the conventional type. Included is the caseJ(n)=n ^–2.Research partially supported by U.S.N.S.F. Grant No. MCS-78-01885.S. Fairchild Scholar at Caltech. On leave from Departments of Mathematics and Physics, Princeton University, Princeton, New Jersey 08544.     

Geometric structure and electron spectrum of YSi n − clusters (n = 6–17)

Results of the optimization of the geometric structure of YSi _n ^? anion clusters (n = 6–17) have been presented and their electron spectra have been calculated. Calculations have been performed by the density functional theory method. Actual geometric structures of clusters have been established by comparing the calculated and known experimental data.     

q-analog ofA m−1 ⊕A n−1 ⊂A mn−1

A natural embeddingA _m–1 A _n–1 A _mn–1 for the corresponding quantum algebras is constructed through the appropriate comultiplication on the generators of each of theA _m–1 andA _n–1 algebras. The above embedding is proved in theq-boson realization by means of the isomorphism between theA _q ^– (mn ~ ⁿ A _q ^– (m) ~ ^m A _q ^– (n)algebras.     

Study of Fermilab data for the reaction π− p→ηn

Fermilab data for the angular distribution measurements of the reaction ^– p n are investigated and it is shown that a good fit with experiment is obtained by using a simple Regge pole model with phenomenological residue functions. The energy dependence in this case is found to be different from that for the d/dt/ data obtained at Serpukhov.Work supported by the Pakistan Science Foundation under contract No. P-PU-PHY(11/1).     

Mössbauer study of the HgBa2Ca n−1CunO2n+2 ceramics

The parameters of the electric-field gradient tensor at the copper, barium, and mercury sites in the HgBa₂Ca _n?1Cu_nO_2n+2 lattices (n=1,2,3) have been determined by Mössbauer emission spectroscopy on the ⁶⁷Cu(⁶⁷Zn), ¹³³Ba(¹³³Cs), and ¹⁹⁷Hg(¹⁹⁷Au) isotopes, and calculated in the point-charge approximation. An analysis of these results combined with available ⁶³Cu NMR data showed that the experimental and theoretical data can be reconciled by assuming that the holes originating from defects in the material are localized primarily on the sublattice of the oxygen lying in the copper plane [for HgBa₂Ca₂Cu₃O₈, in the plane of the Cu(2) atoms].     

Spatial and electronic structures of the germanium-tantalum clusters TaGe n − (n = 8–17)

The results of optimizing the spatial structure and calculated electronic spectra of the TaGe _n ^? anion clusters (n = 8–17) have been presented. The calculations have been performed in terms of the density functional theory. The most probable spatial structures of clusters detected in the experiment have been determined by comparing the calculated and available experimental data.     

Bottom-up substitution assembly of AuF4−n0,−+nPO3 (n = 1–4): a theoretical study of novel oxyfluoride hyperhalogen molecules and anions AuF4−n(PO3)n0,−

Compounds with high electron affinity, i.e. superhalogens, have continued to attract chemists’ attention, due to their potential importance in fundamental chemistry and materials science. It has now proven very effective to build up novel superhalogens with multi-positively charged centres, which are usually called ‘hyperhalogens’. Herein, using AuF₄^? and PO₃ as the model building blocks, we made the first attempt to design the Au,P-based hyperhalogen anions AuF_4?n(PO₃)_n^? (n = 1–4) at the B3LYP/6-311+G(d)&;SDD and CCSD(T)/6-311+G(d)&;SDD (single-point) levels (6-311+G(d) for O, F, P and SDD for Au). Notably, for all the considered Au,P systems, the ground state bears a dioxo-bonded structure with n ≤ 3, which is significantly more stable than the usually presumed mono-oxo-bonded one. Moreover, the clustering of the –PO₃ moieties becomes energetically favoured for n ≥ 3. The ground states of AuP₄O₁₂^0,? are the first reported cage-like oxide hyperhalogens. Thus, the ?PO₃ moiety cannot be retained during the ‘bottom-up’ assembly. The vertical detachment energy (VDE) value of the most stable AuF_4?n(PO₃)_n^? (n = 1–4) ranges from 7.16 to 8.20 eV, higher than the VDE values of the corresponding building blocks AuF₄^? (7.08 eV) and PO₃^? (4.69 eV). The adiabatic detachment energy values of these four hyperhalogens exceed 6.00 eV. Possible generation routes for AuF_4?n(PO₃)_n^? (n = 1–4) were discussed. The presently designed oxyfluorides not only enriches the family of hyperhalogens, but also demonstrates the great importance of considering the structural transformation during the superhalogen → hyperhalogen design such as for the present Au–P based systems.     

Ionization-excitation of helium into the np (n = 2−5) states

Cross sections for the simultaneous ionization and excitation to the np states (n = 2−5) of the helium atom by fast proton and antiproton impact have been calculated. We have applied the impact parameter method and have used second-order perturbation approximation. Electron correlation has been taken into account in the initial state but has been neglected in the final state. Our cross sections are compared to the experimental data.     

n - \bar n transitions in nuclei and mixing of nuclear states with A and A−22

A new lower limit on the period of oscillations, sec, which follows from the stability of Fe, is found. This limit is almost 10 times larger than previous estimations. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 7, 456–461 (10 October 1996) This paper is an extended version of the talk presented at the Workshop on Baryon Instability Searches, Oak Ridge, March 1996. Published in English in the original Russian journal. Edited by Steve Torstveit.     

Study of fermilab data for the reaction π−p → π0n

Fermilab data for the angular distribution measurements of the reaction ^–p ⁰n are investigated and it is shown that a good fit with experiment is obtained by using a simple Regge pole model with phenomenological residue functions. The energy dependence in this case is found to be different from that for the d/dt data obtained at Serpukhov.Work supported by the Pakistan Science Foundation under contract No. P-PU-PHY(11/1).     

On momentum dependence of the reaction π− p→ωn near threshold

We discuss the near–threshold behavior of the ω production amplitude in the reaction π⁻ p→ωn. In contrast to the results of earlier analyses we find that the averaged squared matrix element of the production amplitude must be a decreasing function of energy in order to describe the existing experimental data. Received: 11 August 1999     

High performance p−n junctions in the LPE MnxCdyHg1−x−y Te layers

The electric properties of n⁺−p Mn_xCd_yHg,_1−x−yTe photodiodes with a cut-off wavelength of λ_co ∼ 3.3–3.8 μm at 77 K have been studied. The p−n junctions were created using ion implantation of boron into the p-type LPE epitaxial layers. Zero bias resistance-area product at T = 85 K is equal to 1.7 × 10⁷ Ω ·. cm² for the best sample (λ_co = 3.8 μm). For the material under study, this surpasses the values which have been reported up until now for a given spectral region, and is comparable with those of the best Cd_xHg_1−xTe diodes with similar energy gap values. Mechanisms of current flow through the p−n junctions at 77 < T < 200 K without and under background illumination are discussed.     

A study of K−π+ scattering in the reaction K−p→K−π+n at 11 GeV/c

Results from a high statistics study of the reaction K⁻p→K⁻π⁺n are presented. These results are based on data obtained with an 11 GeV/c beam using the LASS spectrometer at SLAC. The mass dependence of the spherical harmonic moments provides clear evidence for the production of the complete leading orbitally excited K¹ series up through J^P = 5⁻. These moments are used to perform an energy independent partial wave analysis of the K⁻π⁺ system from threshold to 2.6 GeV/c² using a t-dependent parametrization of the production amplitudes. The amplitudes corroborate the leading K¹(892), K₂¹(1430), K₃¹(1780), K₄¹(2060), and K₅¹(2380) resonances observed directly in the moments, and also provide new evidence for underlying states. The 0⁺ amplitude contains the K₀¹(1350) and a second 0⁺K¹(1950) at higher mass. The 1⁻K¹(1790) seen earlier two and three-body analyses is confirmed, and evidence is provided for suppressed K⁻π⁺ decay mode of a second 1⁻ state, the K¹(1410), which has been seen in earlier three-body analyses.     

In-plane London penetration depths near the critical temperature of Tl2Ba2Ca n−1Cu n O2n+4 and (Bi,Pb)2Sr2Ca n−1 Cu n O2n+4 (n=2,3)

From isothermalM(H) curves nearT _c , measured on polycrystalline Tl₂Ba₂Ca _n–1Cu _n O_2n +4 and (Bi, Pb)₂Sr₂Ca _n–1Cu _n O_2n+4 (n=2,3) samples, we deduce the in-plane penetration depths _ab as functions of temperature. An estimate according to the BCS weak-coupling clean-limit fit, which produces the data nearT _c very well, yields _ab(0)=3100 Å, 2320 Å 2210 Å, and 1960 Å for Bi₂Sr₂CaCu₂O₈, Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀, Tl₂Ba₂CaCu₂O₈, and Tl₂Ba₂Ca₂Cu₃O₁₀, respectively. A comparison between strong-coupling and weak coupling fitting curves clearly favours the weak-coupling temperature dependence of _ab nearT _c .