Ground state energy of small electron-hole drops

The ground state energy of small electron-hole drops is calculated for droplets ranging in size from 10 to 10,000 pairs. A new value for the bending energy of $\text{1.1×10}{}^{\mathrm{?10}}\text{erg}\text{cm}$ is derived. We also give a simple highly accurate formula for the total energy per pair. The surface energy is extracted from the total energy and found to agree well with a previous self-consistent calculation. The density at the center of the drop remains essentially constant over the entire range of N, indicating that the drop is not dramatically compressed by the surface tension.     

Current injected electron-hole plasma in GaP pin-device structures

We report first on an electrically generated electron-hole plasma (EHP) in GaP light emitting diodes having a pin-structure. For current densities above j ? 10³Acm^?2 and at T = 77 K a dense EHP is formed within the i-region whose carrier density can easily be changed by the injection level. The corresponding electron-hole pair densities n of the plasma and the resulting gap shrinkage ΔE_g have been determined using a least-squares fit of the EHP luminescence spectra. The lineshape analysis of the spectra yields a $\text{n}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$ -dependence of the gap shrinkage in quantitative agreement with findings from optically excited EHP and corresponding theoretical work. From electrical investigations it can be concluded that the EHP causes a strong nonlinear behaviour of the current-voltage characteristics.     

Limit cycle in a bound exciton recombination model in non-equilibrium semiconductors

A non-equilibrium semiconductor model involving the processes of photogeneration of electron-hole pairs (e-h) (rate G), stimulated creation of excitons from e-h (rate constant C) and decay of excitons on recombination centres (rate constant k) is analyzed in this paper for steady states and limit cycle behaviour. Considering the exciton decay to be similar to enzymatic processes in chemical reactions obeying a Michaelis-Menten law, and choosing units such that k = 1 = N, where N is the concentration of recombination centres, the model represents a 2-parameter (C and G) 2-dimensional (exciton and electron-hole concentrations x, n) dynamical system with a unique steady state (x₀,n₀) which is unstable in the region (l ? G)³?4C, the equality sign corresponding to the bifurcation curve in parameter space. In the region (l ? G)³ > 4C the system displays a unique stable limit cycle which is obtained in analytical form by employing a two-time-scales method for parameters in the neighbourhood of the bifurcation curve. The limit cycles are tilted ellipses with angular frequency $\text{}\text{?}$gw of the order of 10⁶ s^?1. In a realistic semiconductor situation G$\text{\$}\text{?}$10^?3.     

A recombination model for large-PT reactions

A difficult theoretical problem in large P_T reactions is to reproduce simultaneously the observed single-particle distributions and the distribution of 〈P_out〉² versus X²_E for different values of $\text{s}$ and P^trig_T. The purpose of this letter is to report successful fits to these distribution in a “recombination” model and to present the predictions of the model at $\text{s}\text{=540}\text{GeV}$, corresponding to the CERN PP? collider.     

Anomalous specific heat of dipolar spin glasses and ferroelectrics

We show that for a random Ising model with 1/R³ interactions, the probability distribution of molecular field p(H) goes to zero as H tends to zero. We suggest that p(H) ～ H^{$\text{1}\text{2}$} for small H. Monte Carlo calculations of p(H) for the model are performed with results consistent with this suggestion. These results are used to explain the anomalous T^{$\text{3}\text{2}$} specific heat observed in alkali halides containing off-center ions, and in ferroelectrics.     

Plasma dynamics in GaAs under strong picosecond surface excitation

We have investigated the time-resolved luminescence of GaAs in air at room temperature, under strong picosecond surface excitation. The energy density was in the range 4–40 $\text{mJ}\text{cm}{}^2$ and the excitation wavelength λ_ex ? 0.53 μ. The peak temperature reached by the generated electron-hole plasma at the end of the excitation pulse amounts to T_M ? 720 K at an energy density of about 10 $\text{mJ}\text{cm}{}^2$. Further increase of the power induces surface damage on the sample. The plasma relaxes its kinetic energy at a slow rate of the order of 10¹⁰$\text{eV}\text{s}$, supporting our previous calculations which concluded that electron-phonon interactions are strongly screened by intravalley free-carrier collisions at high plasma density, so that the plasma cooling slows down.     

Change of photon statistics due to multi-photon absorption

Simple approximative equations governing the temporal behaviour of both the mean photon number, $\text{n}$, and its mean square deviation, Δn², in the process of k-photon absorption (k = 1, 2, …) are derived and solved for initial photon distributions characterized by $\text{n}$ ? 1 and Δn² ? $\text{n}$^-2. It is readily shown that such an initial distribution, in the course of attenuation, tends to a distribution for which $\text{Δn}{}^2\text{= k (2 k - 1)}{}^{-1}\text{n}$. Hence, for k > 1, the distribution is narrower than a Poisson distribution which means that photon antibunching occurs. The feasibility of a Hanbury Brown and Twiss type experiment allowing to detect this effect utilizing two-photon absorption is discussed, and an estimation of the required order of magnitude of the two-photon absorption cross-section is presented.     

Anomalous frequency dependence of giant quantum attenuation in Bismuth below 1 K

Giant quantum attenuation of longitudinal sound waves in Bi has been measured at temperatures down to 8 mK for the case that the electron (n = 0, s = + 1) and hole (n = 1, s = ? 1) Landau levels cross simultaneously Fermi level at a field of about 90 kOe. The temperature and frequency dependences of the peak attenuation due to these two levels are expressed by α_p ∝ T^-μω^ν with $\text{μ ? 1}$ and $\text{ν ? 1}$ at T > 1 K. When T ? 1 K the value of μ decreases by decreasing temperature and below 0.1 K, α_p takes almost constant value. At T ? 0.5 K, ν becomes larger than 1 and maximum value of ν observed is 2 at T ～ 0.05 K. These features of the attenuation peak at very low temperatures are consistent with what are expected in the fluctuation region of the gas-liquid type transition of the electron-hole system.     

Radiative decays of the Jψ and evidence for a new heavy resonance

The three photon final state produced in e⁺e^? collisions has been measured at the mass of the $\text{J}\text{ψ}$ resonance using the nonmagnetic part of the double arm spectrometer DASP. The decays $\text{J}\text{ψ}\text{→ ηγ, η'γ}$ and π^oγ were observed and their branching ratios are given. A four standard deviation signal was observed in the γγ mass spectrum at a mass of (2.83 ± 0.03) GeV. An upper limit is given for the direct decay $\text{J}\text{ψ}\text{→ 3γ}$.     

Optical absorption by neutral bound excitons

In this note we determine the oscillator strengths for the dipole absorption of neutral bound excitons in direct gap semiconductors, using our previously obtained 35-term Page and Fraser type wave function, and taking into account the detailed electronic structure as well as the electron-hole exchange interaction.The envelope part of the oscillator strengths varies considerably with the electron-hole mass ratio $\text{σ =}\text{m}{}^1{}_{\mathrm{e}}\text{m}{}^1{}_{\mathrm{h}}$, and is maximum for the (D⁰, X)- complex when σ = 0.4. For typical σ-values (σ? 0.1–0.2), . But when σ approaches zero, the overlapping of the electron and the hole envelope wave functions of the (A⁰,X)-complex decreases progressively so that the oscillator strength also decreases and tends to zero.In the case of zinc-blende materials (T_d) and positive spin-orbit coupling at $\text{k}\text{= 0}$, we confirm that the line strength for transitions to or from $\text{J =}\text{1}\text{2}\text{(Γ}{}_6\text{)}$ or $\text{J =}\text{5}\text{2}\text{(Γ}{}_7\text{+ Γ}{}_8\text{)}$ level of the (A⁰, X)-complex is equal to one quarter of the line strength to or from the $\text{J =}\text{3}\text{2}\text{(Γ}{}_8\text{)}$ level.In the case of CdS, where our computed values are only in qualitative agreement with the experimental values, we discuss the use of the phenomenological result of Rashba.     

Single diffraction dissociation at the CERN SPS collider

The reaction $\text{p}\text{p}\text{→}\text{p}\text{X}$ was studied at a centre-of-mass energy $\text{s}\text{= 540}\text{GeV}$ by measuring the momentum spectrum of the antiproton. Data are presented in the four-momentum transfer range 05 < ?t < 1.2GeV². The shape of the mass distribution of the system X shows a diffractive component as already observed at lower energies. The differential cross section scales approximately with energy when compared to the ISR data.     

States in 163Dy and 169Er populated in the (t,p) reaction

Angular distributions of protons from the ¹⁶¹Dy(t, p)¹⁶³Dy and ¹⁶⁷Er(t, p)¹⁶⁹Er reactions were studied, using 15 MeV and 17 MeV tritons from the McMaster University tandem Van de Graaff accelerator. The reaction products were analyzed with a magnetic spectrograph and detected with nuclear emulsions. Since the ¹⁶¹Dy target ground state is the $\text{5}\text{2}$⁺[642] orbital, a strong L = 0 transition was observed to the $\text{5}\text{2}$⁺[642] bandhead in ¹⁶³Dy, which was previously assigned at 251 keV. Also transitions to the $\text{7}\text{2}$, $\text{9}\text{2}$ and $\text{11}\text{2}$ band members were observed. Similarly, a strong L = 0 transition was observed to the $\text{7}\text{2}$⁺[633] bandhead at 244 keV in ¹⁶⁹Er, with the other band members only weakly populated. The angular distributions to the various members of these two bands can be described when higher-order reaction processes are taken into account. In ¹⁶³Dy, surprisingly strong L = 0 transitions were observed to levels at 1831 keV, 1937 keV and 2053 keV, with strengths of 23%, 30% and 37% of that for the $\text{5}\text{2}$⁺[642] bandhead. In ¹⁶⁹Er, the 905 keV level was populated with an L = 0 transition that had 31% of the strength observed for the strong L = 0 transition to the 244 keV level. The nature of these states is at present not understood.     

Coulomb excitation of 115Sn

Coulomb excitation of the nucleus ¹¹⁵Sn was studied with beams of ⁴He and ¹⁶O. Level energies, spins, mean-lives and B(E2) and B(M1) transition probabilities were obtained. Spin $\text{3}\text{2}$⁺ states were observed at 497.35 and 1280.08 keV and spin $\text{5}\text{2}$⁺ states were observed at 986.54 and 1416.78 keV. A state of 612.79 keV was observed to be indirectly excited by decay of the Coulomb excited states. Eleven B(E2) values and nine B(M1) values were obtained for the transitions between the low-lying states. In contrast to previous particle transfer results which suggested a clear distinction between shell-model and collective $\text{3}\text{2}$⁺ and $\text{5}\text{2}$⁺ states, our results suggest the collective strength is shared by the two $\text{3}\text{2}$⁺ and two $\text{5}\text{2}$⁺ states.     

Electroabsorption in TlInS2

Electroabsorption spectra of single crystals have been studied near the fundamental absorption edge at 77 and 300 K. At 300 K two positive peaks (2.34 and 2.42 eV) and a negative peak (2.38 eV) are observed in the electroabsorption spectrum. At liquid-nitrogen temperature a fine structure corresponding to the formation of a parabolic exciton (2.503 eV) is observed.Values of the width of the forbidden gap E_g, the n = 1 exciton positions, the exciton activation energy ΔE_b, the effective Bohr radius a_exc, the reduced effective mass of an electron-hole pair μ, and the exciton ionization field F(E_g = 2.535 eV, E_exc = 2.503 eV, E_b = 32 meV, $\text{a}{}_{\mathrm{<mtext>exc</mtext>}}\text{=}\text{28}\text{A}\text{A;}\text{;}$;, μ = 0.15 m₀, and F = 1.2 × 10⁵ V cm^-1) have been determined from the electroabsorption spectrum.     

Structural connections between 148Sm and 149Sm nuclei

The ^{146, 148}Nd(α, χn) and ^{148, 150}Nd(³He, χn) reactions at E_α = 20–43 MeV and E_3He = 19–27 MeV, are used to study excited states in the ¹⁴⁹Sm₈₆ and ¹⁴⁹Sm₈₇ nucleides and consequently the low-spin odd-parity excitation. The mixing ratios and multipolarities of the most prominent transitions are deduced from the combined evidence of angular distribution and electron conversion data. The spin-parity assignments for most of the levels observed are established. In ¹⁴⁸Sm the ground state band extending to I^π = 10⁺ is predominantly populated. A negative-parity odd-spin band extending from I^π = 3^?through 11^? is also observed. The bands in ¹⁴⁸Sm are interpreted within the framework of the interacting boson approximation model. In ¹⁴⁹Sm positive-parity levels with spin up to $\text{25}\text{2}$ and negative-parity levels with spins up to $\text{21}\text{2}$ are observed. The predominant γ-decay proceeds via transitions associated with $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$, $\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$, $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ and $\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ intrinsic configurations. The branching ratios B(E1)/B(E2) are calculated and compared in both ¹⁴⁸Sm and ¹⁴⁹Sm nucleides. The B(E1)/B(E2) dependence on the value of Z for some N = 86 (as well as 88 and 84) isotones showing a minimum of Z = 64 was noted. A 4 ns high-spin isomer mainly decaying into the positive-parity band based on the $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ state in ¹⁴⁹Sm is found. Experimental evidence is presented to interprete the $\text{1}\text{2}{}^{\mathrm{+}}$, $\text{15}\text{2}{}^{\mathrm{+}}$, … and $\text{9}\text{2}{}^{\mathrm{?}}$, $\text{13}\text{2}{}^{\mathrm{?}}$, …, ΔI = 2, sequences in ¹⁴⁹Sm as arising from the coupling of an $\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ neutron to the octupole and quadrupole modes of the ¹⁴⁸Sm core nucleus. The absolute reaction cross sections for the ^{146, 148, 150}Nd(³He, χn) reactions have been determined for different bombarding energies. The mixing of the $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ and $\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ shells is discussed in the framework of an axial-particle-rotor model calculation.     

Phonon wind induced anomalous dependence of the electron-hole drop luminescence in Ge at low magnetic fields

Anomalous variations of EHD luminescence in Ge in low magnetic fields depending on intensity and orientation of excitation are reported. Angular dependent drop size distribution, quantum efficiency $\text{Q}$ and dilution of the initial plasma are derived and shown to result from the anisotropy of the phonon wind. Magnetic field inhibited escape of Auger carriers increases $\text{Q}$ by 20%. Strongly enhanced surface recombination due to magnetic field induced confinement of the carriers is deduced.     

Fission barriers of Pb nuclei at high angular momentum

Fission and evaporation residue excitation functions have been measured after the nuclei ^{192, 195, 198, 200}Pb were formed by the fusion of ^{28, 30}Si with ^{164, 167, 170}Er. The fission probabilities extracted were fitted using the rotating liquid drop/statistical model codes ORNL ALICE and MBII. The range of values of the mass asymmetry, $\text{(N?Z)}\text{A}$, of the fissioning systems allows some restrictions to be placed on the value of the surface asymmetry parameter K_s, used in the liquid drop model, despite the many uncertainties and approximations in the data analysis.     

Coherent production of multimeson final states on A ∼ 20 nuclei by K− of 5.5, 10.0, 12.7 GeV

Coherent production of $\text{K}\text{π,}\text{K}\text{2π}\text{and}\text{K}\text{3π}$ final states from A ～ 20 nuclei by K^? beams of 5.5, 10.0 and 12.7 GeV is analyzed. Final states with ? 2π^O are included. Coherent $\text{K}\text{π}$ production occurs (although forbidden via 0⁺ exchange) and is dominated by the $\text{K}$¹ (890). The shape of the t distribution, the alignment of the produced meson and the ratio of the cross section on nuclei to that on hydrogen are consistent with optical model predictions assuming that $\text{K}$¹ (890) are produced on single nucleons by exchange of isoscalar trajectories of natural parity (J^P = 1^?, 2⁺, etc.) and that the $\text{K}$¹ (890) absorption in nuclear matter equals that of the K^?. Coherent $\text{K}\text{ππ}$ production (allowed via 0⁺, 1^?, 2⁺, etc. exchange) is dominated by the Q phenomenon. A Dalitz plot and angular correlation analysis yields values for $\text{K}\text{?/}\text{K}{}^1\text{π}$ fractions, and shows that $\text{J}{}^{\mathrm{P}}\text{= 1}{}^{\mathrm{+}}\text{S-wave}\text{K}{}^1\text{π}$ dominates the coherently produced Q. The helicity of the Q is found to be compatible with 0. The Q^? -nucleaon total cross section is estimated to be 0.98_?0.37⁺⁰²⁴ times the $\text{K}$^? -nucleon total cross section from a comparison of the coherent Q-production cross section with corresponding hydrogen cross sections at 10 and 12.7 GeV. We observe coherent production of $\text{K}$ω. The ration $\text{K}\text{ω/}\text{K}\text{ππ}$ coherently produced in the Q mass region is (4 ± 1)%. Coherent production of $\text{K}{}^{\mathrm{?}}\text{π}{}^{\mathrm{+}}\text{π}{}^{\mathrm{?}}\text{and}\text{K}{}^{\mathrm{<mtext>O</mtext>}}\text{π}{}^{\mathrm{+}}\text{π}{}^{\mathrm{?}}\text{π}{}^{\mathrm{<mtext>O</mtext>}}$ is observed in the L region. Coherent production is not observed in the K4π channels.     

Magnetic moments of the 12+ isomeric states in 194, 196, 198Pb

The g-factor of the 12⁺ isomeric state in lead isotopes with A = 194, 196, 198 was measured using the time-differential perturbed angular distribution method (TDPAD). The values obtained are respectively g(194) = ?0.158(6); g(196) = ?0.157(7); g(198) = ?0.144(11). A more precise determination of the 12⁺ level half-life is also made. The g-factprs of these nuclear states, which are described with v(i_{$\text{13}\text{2}$})^?2 as the main configuration, are surprisingly constant over a large mass range (between A = 206 and 194). A core polarization analysis explains this trend: the polarization induced on neutrons in i_{$\text{13}\text{2}$} orbit decreases with the mass number A (blocking effect), but a compensation is provided by the other spin-orbit partners f_{$\text{7}\text{2}$}-f_{$\text{5}\text{2}$} and P_{$\text{3}\text{2}$}-P_{$\text{1}\text{2}$}.     

Analyzing powers for the (p, α) reactions on 58, 60, 62Ni at Ep = 22 MeV

Measurements of both the analyzing power and cross section were made for the (p, α) reactions on ^58,60,62Ni at an incident energy of 22 MeV. Data were taken for the strongly populated proton-hole states (0f_{$\text{7}\text{2}$}, 1s_{$\text{1}\text{2}$} and 0d_{$\text{3}\text{2}$}) in the residual cobalt isotopes and for 8 weakly populated low-lying states in ⁵⁵Co and ⁵⁹Co. Angular distributions were taken between θ_lab = 10° and 140° for the ground state and θ_lab = 10° and 80° for the excited states. Both the cross sections and analyzing powers exhibit a similar angular distribution for states having the same J^π values except in the transition to the $\text{3}\text{2}$^? state in ⁵⁹Co at 1.099 MeV. Using the observed J-dependence of the analyzing power, the unknown J^π values for the states at 2.982 MeV in ⁵⁵Co and 3.090 MeV in ⁵⁹Co are assigned to be $\text{9}\text{2}$^?. The shapes of the differential cross sections were well reproduced by the zero-range DWBA calculations using a triton-cluster form factor. However, all the measured analyzing powers could not be reproduced within the framework of such a simple DWBA calculation.