Overlap Integrals Of Wave Functions Research Articles

Localized interlayer complexes in heterobilayer transition metal dichalcogenides

We present theoretical results for the radiative rates and doping-dependent photoluminescence spectrum of interlayer excitonic complexes localized by donor impurities in MoSe$_2$/WSe$_2$ twisted heterobilayers, supported by quantum Monte Carlo calculations of binding energies and wave-function overlap integrals. For closely aligned layers, radiative decay is made possible by the momentum spread of the localized complexes' wave functions, resulting in few $\mu$s$^{-1}$ radiative rates. For strongly misaligned layers, the short-range interaction between the carriers and impurity provides a finite radiative rate with a strong asymptotic twist angle dependence $\propto \theta^{-8}$. Finally, phonon-assisted recombination is considered, with emission of optical phonons in both layers resulting in additional weaker emission lines, redshifted by the phonon energy.

Laser Operation of Nitride Laser Diodes with GaN Well Layer in 340 nm Band

We have reported the laser operation of a short-wavelength ultraviolet laser diode with multiple quantum wells composed of GaN well layers. The GaN well-width is estimated to be around 1–1.5 nm. We have simulated whole laser-diode structure, and calculated wave-function overlap integrals. It is provided the integral becomes the maximum value in the well-width of 1.5 nm. The laser operation has been achieved in 340-nm-band under the pulsed current mode at room temperature. The wavelength is far from the wavelength corresponding to band gap of GaN, and the shortest lasing wavelength ever reported for a semiconductor laser composed of binary compound well layer. Moreover, the device has been realized on an Al0.2Ga0.8N underlying layer with 0.1 lower AlN mole fraction margin than that of a previous reported 342 nm laser-diode with an Al0.3Ga0.7N underlying layer. These results provide a chance to the next stage for a shorter-wavelength ultraviolet laser diode.

Clustering Pre-equilibrium Model Analysis for Nucleon-induced Alpha-particle Spectra up to 200 MeV

The clustering exciton model of Iwamoto and Harada is applied to the analy- sis of pre-equilibrium (N; x ) energy spectra for medium-to-heavy nuclei up to 200 MeV. In this work, we calculate alpha-particle formation factors without any approximations that appear in the original model. The clustering process is also considered in both the primary and second pre-equilibrium emissions. We optimize the exciton and the cluster- ing model parameters simultaneously by looking at the experimental (N; xN) and (N; x ) energy spectra. The experimental alpha-particle spectra are well reproduced with a unique set of clustering model parameters, which is independent of incident neutrons/protons. The present analysis also implies that the clustering model parameter is not so di erent between the medium and heavy nuclei. Our calculations reproduce experimental data gen- erally well up to the incident energy of 150 MeV, but underestimations are seen above this energy. The exciton model, as it is frequently used in the nuclear data evaluation (1), predicts pre-equilibrium (N; xN) spectra generally well. However, a long-standing problem exists in the model calculation of the pre-equilibrium composite-particle spectra due to rather complicated reaction mechanism. The phenomenological models proposed by Kalbach (2,3) describe nucleon-transfer reaction process in the phase-space, in which many adjustable parameters are involved to fit experimental particle energy- spectra. Although a useful global parameterization is reported (2,3), extrapolation of the global pa- rameters beyond the experimental range needs much attention. We apply the clustering exciton model of Iwamoto and Harada (4) to calculate nucleon-induced pre-equilibrium alpha-particle spectra from medium-to-heavy nuclei. The model describes the pickup process within the exciton model framework, where the alpha-particle formation factor is calculated by the overlap integral of wave functions between the alpha-particle and four nucleons (include the nu- cleons below Fermi level). In this work, the formation factors are calculated by numerical integrations, while the original Iwamoto-Harada model employed the root-mean-square approximation (4) where no correlation exists between the coordinates in the phase-space. The clustering process is also con- sidered in both the primary and second pre-equilibrium emissions. We optimize the pre-equilibrium and the clustering model parameters simultaneously by looking at the experimental nucleon and alpha- particle energy spectra. In this paper, di erences between the exact calculation and the approximation are exhibited for the alpha-particle formation factor. Through the comparisons with experimental spectra at incident energies up to 200 MeV, we show the behavior of the clustering model parameter, the applicability and limitation of the model.

Band Interaction between Chiral Doublet Bands

Band interaction between the chiral doublet bands based on πh11/2 ⊗ vh−111/2 configuration is investigated in the particle rotor model with different triaxial deformation γ. The variation of chiral partner states with γ values is understood qualitatively based on the basic picture of two interaction levels, which is confirmed further by the calculated overlap integral of wave functions at different γ values. It is found that the interaction strengths of chiral partner states are obviously different for odd spins and even ones.

Many-body design of highly strained GaInNAs electroabsorption modulators on GaInAs ternary substrates

Electroabsorption in highly strained GaInAs and GaInNAs quantum wells (QWs) grown on GaInAs or quasi-GaInAs substrates is investigated by using microscopic many-body theory. The effects of various parameters, such as strain, barrier height, substrate composition, and temperature are thoroughly examined. It is shown that the value of the absorption coefficient strongly depends on the depth of the QWs under large bias electric field due to the small overlap integral of wave functions between the conduction and valence bands. The use of GaInNAs QWs makes the strain in the well layer very small. Further, the effective quantum-well depth is increased in GaInNAs QWs due to the anticrossing interaction between the conduction and N-resonant bands, making it possible to obtain larger absorption coefficient under large bias electric fields without using wide-band gap materials for barriers.

Flavor physics in the Randall-Sundrum model I. Theoretical setup and electroweak precision tests

A complete discussion of tree-level flavor-changing effects in the Randall-Sundrum (RS) model with brane-localized Higgs sector and bulk gauge and matter fields is presented. The bulk equations of motion for the gauge and fermion fields, supplemented by boundary conditions taking into account the couplings to the Higgs sector, are solved exactly. For gauge fields the Kaluza-Klein (KK) decomposition is performed in a covariant R_xi gauge. For fermions the mixing between different generations is included in a completely general way. The hierarchies observed in the fermion spectrum and the quark mixing matrix are explained naturally in terms of anarchic five-dimensional Yukawa matrices and wave-function overlap integrals. Detailed studies of the flavor-changing couplings of the Higgs boson and of gauge bosons and their KK excitations are performed, including in particular the couplings of the standard W and Z bosons. A careful analysis of electroweak precision observables including the S and T parameters and the Zbb couplings shows that the simplest RS model containing only Standard Model particles and their KK excitations is consistent with all experimental bounds for a KK scale as low as a few TeV, if one allows for a heavy Higgs boson and/or for an ultra-violet cutoff below the Planck scale. The study of flavor-changing effects includes analyses of the non-unitarity of the quark mixing matrix, anomalous right-handed couplings of the W bosons, tree-level flavor-changing neutral current couplings of the Z and Higgs bosons, the rare decays t-->c(u)+Z and t-->c(u)+h, and the flavor mixing among KK fermions. The results obtained in this work form the basis for general calculations of flavor-changing processes in the RS model and its extensions.

Photoluminescence Properties Affected by Carrier Transport between X and Different First Excited States Originating from Interface Imperfection in GaAs/AlAs Multi-Quantum Wells

The authors investigated the electric-field dependence of photoluminescence (PL) spectra in a GaAs/AlAs multi-quantum well (MQW) structure, in which QWs with different thicknesses coexist. PL properties in this sample are chiefly determined by the coexistence of 21-monolayer (ML) and 23-ML QWs, because the islands of 22-ML QWs are too small to have an effect on radiative processes. Two PL signals are found in the shorter-wavelength region, caused by X1–Γ2 resonances, because the different thicknesses of GaAs QWs lead to different resonant voltages and wavelengths. We also estimated the carrier densities of excited states from the observed two PL intensities and by calculations of overlap integrals of wave functions between electron and heavy-hole states. This result clearly indicates that the carrier density in the Γ2 in the 21-ML QW becomes larger than that in the 23-ML QW when the X1–Γ2 resonance of the 21-ML QW occurs. This demonstrates that interface imperfection creates novel carrier transport paths and affects carrier densities as well as optical properties in excited states in MQW structures.

Anomalous Sharp Dip of Large Field-Induced Refractive Index Change in GaAs/AlGaAs Five-Layer Asymmetric Coupled Quantum Well

The five-layer asymmetric coupled quantum well (FACQW) is a new potential-tailored quantum well for ultrafast and low-voltage optical modulators and switches. Almost linear and large electrorefractive index change can be obtained in the transparency wavelength regions. In the GaAs/AlGaAs FACQW, an abrupt change in refractive index change Δn due to an applied electric field F occurs at a certain electric field range, which results in an anomalous sharp dip of Δn versus F. The physical origin and the elimination of the dip are discussed in detail. The abrupt change of refractive index is caused by significant changes of the wavefunction overlap integrals (and exciton binding energies) of transitions between the ground states for an electron (e1) and a heavy hole (hh1), and transitions between e1 and the first excited state for a heavy hole (hh2). The overlap changes are mainly due to shifts of the wavefunction distribution of hh1 and hh2, respectively. The dip can be eliminated by changing the position or Al content of the AlGaAs barrier layer in the FACQW. In addition, the larger negative index change in a modified FACQW structure is demonstrated.

Effect of a metal ion on intramolecular spin exchange in spin-labeled complexes

The characteristic features of intramolecular spin exchange in 14 complexes of AgI, HgII, NiII, PdII, PtII, AuIII, and PtIV with spin-labeled ligands were studied by ESR spectroscopy. The measured values of the exchange integral ‖J‖ and the differences between the enthalpies of the efficient conformations (ΔH) were compared with the electronic polarization (refraction)R f of the NiII, PdII, and PtII ions and Klopman's rigidity parameters σK, which characterize the total polarazibility of the ions and the degree of covalence of the bond between the metal atom and the donor atom of the ligand, respectively. Delocalization of the electron spin density and the efficiency of spin exchange are determined by the relative contributions of the s, p, and d orbitals, which produce the overlap integral of wave functions, ‖J‖, and by the geometric features of the coordination polyhedron, which affect the mutual orientation of the N−O fragments.

A New Approach to the Estimation of Accuracy of Calculations of Vibrational Wavefunctions and Radiative Parameters

Abstract The modified method of solving the radial Schrödinger equation, proposed earlier by the authors, is used for developing a new approach to the estimation of accuracy of calculating the vibrational wavefunction overlap integrals for diatomic molecules. Such an approach is shown to allow to separate quantitatively three major sources of errors arising in calculations of the overlap integrals.

Band-to-band Auger processes in 1.3 µm InGaAsP semiconductor lasers

Within the context of the four-band Kane model, we have analyzed the contributions of pure collision and phonon-assisted CHSH and CHCC Auger processes to the nonradiative recombination lifetime in highly excited InGaAsP. Our method incorporates refined expressions for the wavefunction overlap integrals and spectral density functions, and avoids approximations to Fermi and phase-space factors. Our results are in good agreement with recent experiments, despite a rather large uncertainty associated with the unavailability of precise values for certain band-structure parameters.

A numerical analysis of Auger processes in p-type GaAs

We calculate the contributions of pure collision and phonon-assisted Auger processes within the framework of the Kane model to the nonradiative lifetime of p-doped GaAs. Our approach employs refined expressions for the wavefunction overlap integrals. Further, in contrast to previous treatments, our theory correctly describes the temperature dependence of the optical phonon-assisted Auger processes. Our values for the Auger lifetimes are in good agreement with experimental results.

Nonstrange hyperfine splitting in the relativistic harmonic-oscillator quark model

A mass formula relating the $\ensuremath{\Delta}\ensuremath{-}N$ and $\ensuremath{\rho}\ensuremath{-}\ensuremath{\pi}$ hyperfine splittings is derived within the context of the relativistic harmonic-oscillator quark model. The spring constant, determined from the Regge trajectories, adjusts the wave-function overlap integrals so that reasonable agreement with experiment is obtained. The formula involves the square of the hadron masses and clearly indicates factors due to color, SU(6), and internal quark motion.

Study of excited states of atoms by means of nonorthogonal radial orbitals

Rules are derived for graphical determination of the overlap integral of wave functions and matrix elements of operators of physical quantities. A calculation is made for four-electron atoms in the configuation 1s22s4s using nonorthogonal radial orbitals.