Decoupled bands in odd-mass mercury isotopes

The schemes of the low-lying high-spin states in mercury isotopes with A = 195, 197, and 199 have been studied by γ-ray spectroscopy following (α, xn) reactions on separated platinum targets. Two bands have been excited in each Hg nucleus, one with positive parity based on the isomeric i$\text{13}\text{2}$. state and one, probably with negative parity, starting at spin $\text{case21}\text{2}$. The positive-parity states are interpreted with the rotation-aligned coupling scheme as decoupled bands; this implies oblate deformation in these three Hg isotopes. The negative-parity states are discussed as a decoupled i$\text{13}\text{2}$ neutron state coupled to the 5^?, 7^?, 9^?,…states, recently discovered in doubly even mercury isotopes.     

A description of decoupled bands using the angular momentum projection method applied to the coherent phonon state

The decoupled bands of the odd-A La-isotopes are described by the angular momentum projection method. The coherent phonon state is assumed for the intrinsic wave function of the core. The present model covers the particle-vibrator and the particle-rotor coupling model. The results are in good agreement with the experimental energy spectra.     

Strongly coupled bands as “effectively” decoupled bands

We present experimental evidence which suggests that almost all the strongly coupled bands in the rare-earth region may also be treated as “effectively” decoupled bands. In contrast to the usual decoupled bands, the strongly coupled bands seem to arise from a system where a particle carrying an “effective” angular momentumj′ is aligned to an even-even core having an “effective” rotational angular momentumR′ which is not necessarily zero for the band head but may even haveR′=2 or, 4 or, 6?etc. We attempt to explain these observations in a simple physical picture whereinJ _R, the projection ofj, the particle angular momentum, on the rotation axis, is taken as the effectively aligned spin of the last particle. Preliminary results from schematic bandmixing calculations forh _9/2 andf _5/2 orbitals with the Fermi energy lying near the highK single particle levels indeed reveal the existence of “effectively” decoupled bands which seem to agree with this physical picture.     

Measurement of NO22B2 state g values by optical radio frequency double resonance

The g values for some selected levels of the NO₂ 6126 and 5933 Å bands were measured using optical radio frequency double resonance. The g values are found to be well described by the Hund's case (b) coupling scheme.     

Approximation of a general singular vertex coupling in quantum graphs

The longstanding open problem of approximating all singular vertex couplings in a quantum graph is solved. We present a construction in which the edges are decoupled; an each pair of their endpoints is joined by an edge carrying a δ potential and a vector potential coupled to the “loose” edges by a δ coupling. It is shown that if the lengths of the connecting edges shrink to zero and the potentials are properly scaled, the limit can yield any prescribed singular vertex coupling, and moreover, that such an approximation converges in the norm-resolvent sense.     

Spectroscopy and lifetime measurement of high spin states in 73Se

The nucleus ⁷³ Se was studied by the reaction ⁵¹ V(²⁸ Si,αpn)⁷³ Se. The level scheme extended upto $\frac{{41}} {2}\bar h $ in both +ve and ?ve parity bands with 10 new transitions placed in the level scheme. Lifetimes of 17 high spin states measured by DSAM. The transitional quadrupole moment is found to drop down after the band crossing suggesting a less deformed configuration. At the band crossing region, Q _t increases suddenly in both +ve and ?ve parity bands. It is argued that the +ve parity band is a decoupled band.     

Quantum switch for coupling highly detuned superconducting qubits

We propose to implement a quantum switch scheme for coupling highly detuned superconducting qubits connected by a gap-tunable bridge qubit. By modulating the frequency of the bridge qubit, it can be used as a coupler to switch on/off and adjust the coupling strength between the initially non-interaction qubits. It is shown that the proposals of quantum information transfer and quantum entangled gate between two highly detuned qubits can be implemented with high fidelity. Moreover, we extend the case of coupling the switch to multiple qubits for the generation of W states. The advantages of our scheme are that it eliminates the need for tuning the gaps of the qubits and the cross-talk interaction is greatly suppressed. The influence of decoherence and parameter variation is also investigated by numerical simulation, which suggests that the present scheme is feasible in current experiment.     

An iterative method to solve a regularized model for strongly nonlinear long internal waves

We present a simple iterative scheme to solve numerically a regularized internal wave model describing the large amplitude motion of the interface between two layers of different densities. Compared with the original strongly nonlinear internal wave model of Miyata [10] and Choi and Camassa [2], the regularized model adopted here suppresses shear instability associated with a velocity jump across the interface, but the coupling between the upper and lower layers is more complicated so that an additional system of coupled linear equations must be solved at every time step after a set of nonlinear evolution equations are integrated in time. Therefore, an efficient numerical scheme is desirable. In our iterative scheme, the linear system is decoupled and simple linear operators with constant coefficients are required to be inverted. Through linear analysis, it is shown that the scheme converges fast with an optimum choice of iteration parameters. After demonstrating its effectiveness for a model problem, the iterative scheme is applied to solve the regularized internal wave model using a pseudo-spectral method for the propagation of a single internal solitary wave and the head-on collision between two solitary waves of different wave amplitudes.     

Ab initio studies on the electronic structure of CeSi5

We investigated the electronic properties of CeSi₅ by band structure calculation based on the density functional theory within LDA, LDA+U, and fully relativistic schemes. The calculated band structure scheme shows that the spin-orbit coupling splits the Ce 4f states into three manifolds. When the on-site Coulomb potential is added to the Ce-derived 4f orbitals, the degeneracy between the f orbitals would be lifted and they are split into lower Hubbard bands and upper Hubbard bands. It was found that quasiparticle mass enhancement inferred by comparing γ to the density of states (DOS) at the Fermi level indicates the effective mass of CeSi₅ is enhanced with the fully relativistic results.     

Electronic states on the surface of graphite

Graphite consists of graphene layers in an AB (Bernal) stacking arrangement. The introduction of defects can reduce the coupling between the top graphene layers and the bulk crystal producing new electronic states that reflect the degree of coupling. We employ low temperature high magnetic field scanning tunneling microscopy (STM) and spectroscopy (STS) to access these states and study their evolution with the degree of coupling. STS in magnetic field directly probes the dimensionality of electronic states. Thus two-dimensional states produce a discrete series of Landau levels while three-dimensional states form Landau bands providing a clear distinction between completely decoupled top layers and ones that are coupled to the substrate. We show that the completely decoupled layers are characterized by a single sequence of Landau levels with square-root dependence on field and level index indicative of massless Dirac fermions. In contrast weakly coupled bilayers produce special sequences reflecting the degree of coupling, and multilayers produce sequences reflecting the coexistence of massless and massive Dirac fermions. In addition we show that the graphite surface is soft and that an STM tip can be quite invasive when brought too close to the surface and that there is a characteristic tip-sample distance beyond which the effect of sample-tip interaction is negligible.     

Nonlinear statistical coupling

By considering a nonlinear combination of the probabilities of a system, a physical interpretation of Tsallis statistics as representing the nonlinear coupling or decoupling of statistical states is proposed. The escort probability is interpreted as the coupled probability, with Q=1−q defined as the degree of nonlinear coupling between the statistical states. Positive values of Q have coupled statistical states, a larger entropy metric, and a maximum coupled-entropy distribution of compact-support coupled-Gaussians. Negative values of Q have decoupled statistical states and for −2<Q<0 a maximum coupled-entropy distribution of heavy-tail coupled-Gaussians. The conjugate transformation between the heavy-tail and compact-support domains is shown to be for coupled-Gaussian distributions. This conjugate relationship has been used to extend the generalized Fourier transform to the compact-support domain and to define a scale-invariant correlation structure with heavy-tail limit distribution. In the present paper, we show that the conjugate is a mapping between the source of nonlinearity in non-stationary stochastic processes and the nonlinear coupling which defines the coupled-Gaussian limit distribution. The effects of additive and multiplicative noise are shown to be separable into the coupled-variance and the coupling parameter Q, providing further evidence of the importance of the generalized moments.     

A weak coupling model for high-spin states

Weak coupling of a rotating core and an odd particle is used to explain the appearance of pure rotational bands, as well as decoupled aligned state bands by simple geometrical properties.     

Nuclear field theory treatment of K ≠ 0 rotational bands

The properties of the lowest members of K ≠ 0 rotational bands are described as anharmonic vibrational bands. The anharmonicity is calculated by the nuclear field theory (particle-vibration coupling) method. It is shown to be important not to truncate the diagrammatic expansion at a fixed number of vertices. Instead, the way in which the diagrams depend on the number of degrees of freedom participating is used to guide the truncation.     

Optical spectra and a tail in the density of states of the disordered solid solution ZnSe1−c Tec

A calculational scheme is presented to determine the density of states in the fluctuation tail for the disordered solid solution ZnSe_1−c Te_c at concentrations below the threshold for percolation over sublattice sites. Zero-phonon absorption and luminescence bands in the region of the exciton ground state are found using an approach developed earlier. Phonon coupling is taken into account, and vibronic absorption and luminescence bands are obtained. Experimental data are shown to be in a good agreement with the calculations. Fiz. Tverd. Tela (St. Petersburg) 40, 1420–1425 (August 1998)     

A study of the low-lying states in 178Hf through the (n, γ) reaction

The nucleus ¹⁷⁸Hf was studied through thermal neutron and averaged resonance neutron capture reactions. The γ-ray and conversion electrons were measured with high resolution spectrometers. A level scheme up to an excitation energy of ∼2.1 MeV was constructed. It includes ∼65 levels, most of which are ordered into 18 rotational bands. The level scheme is complete up to about 1800keV for spins between 2 and 5. The neutron binding energy was established to be at 7626.3 (3) keV. The consistent Q form of the IBA-1 (CQF) was used to describe the low-lying collective γ and K^π = 0⁺ bands. The agreement with the data was found to be excellent for the energies and B(E2) ratios of the ground and γ bands, whereas the agreement was poor for the K^π = 0⁺ bands.     

Decoupling potentials for the three-body final state Schrödinger equation of knockout reactions

In the conventional distorted wave impulse approximation (DWIA) approach the three-body final state of a knockout reaction is decoupled by assuming a plane wave form for the coupling term. The influence of this decoupling approximation on the analyses of cluster knockout reactions has been investigated for a test case where the exact solution is obtainable. A proper treatment of the coupling term causes large oscillations in the effective distorting optical potentials for the decoupled Schrödinger equation. These decoupling potentials depend strongly not only on the partial wave angular momentum,l but also on their azimuthal projection,m.     

Influence of energy transfer on the intensity pattern of vibronic excitation studied by reduced density-matrix theory

Intensity pattern of the vibronic transitions of a molecular dimer consisting of two molecules interacting through the Coulombic coupling is theoretically studied using a reduced density-matrix approach. The monomeric molecules are assumed to be electronic two-state systems. A single vibration mode with a high frequency and a continuous distribution of low-frequency phonons represented by the Ohmic spectral density are coupled to the electronic transition of the respective molecules. The spin-Boson model is employed to include the effect of electron-vibration and electron-phonon couplings. The intermolecular Coulombic coupling is assumed to be weak (inducing the Förster type of energy transfer process). It is found that, in addition to the well-known excitonic shifts, the intensity of the vibronic side bands reduces with the intermolecular coupling strength in the J-aggregate type of dimer while it increases in the H-aggregate type. When the vibronic bands are blurred by the broadening resulting from the coupling of the electrons to the continuous distribution of the phonons, the absorption line shape shows a wide range of variation depending on the strength of the intermolecular coupling.     

Magnon bands in twisted bilayer honeycomb quantum magnets

We study the magnon bands of twisted bilayer honeycomb quantum magnets using linear spin wave theory. Although the interlayer coupling can be ferromagnetic or antiferromagnetic, we keep the intralayer one ferromagnetic to avoid possible frustration. For the interlayer ferromagnetic case, we find the magnon bands have similar features with the corresponding electronic energy spectrums. Although the linear dispersions near the Dirac points are preserved in the magnon bands of twisted bilayer magnets, their slopes are reduced with the decrease of the twist angles. On the other hand, the interlayer antiferromagnetic couplings generate quite different magnon spectra. The two single-layered magnon spectra are usually decoupled due to the opposite orientations of the spins in the two layers. We also develop a low-energy continuous theory for very small twist angles, which has been verified to fit well with the exact tight-binding calculations. Our results may be experimentally observed due to the rapid progress in two-dimensional magnetic materials.     

A coupling scheme relevant to high angular momenta and intermediate nuclear deformations

Based on the particle-plus-rotor model, it is shown that a new coupling scheme should occur in nuclei under certain conditions. In this coupling scheme, j is quantized along the direction of $\text{I}$ rather than along the symmetry axis. Simple approximate wave functions for this scheme have been developed and compared with the exact solutions of the particle-plus-rotor model.