Terms Of Particle-hole Excitations Research Articles

Unified description of pairing and quarteting correlations within the particle-hole-boson approach

We study the description of single-species and isovector pairing correlations in the framework of the projected-BCS (PBCS) and the Quartet Condensation Model (QCM) from a particle-hole perspective and we introduce the representation of the QCM quartet condensate state in terms of particle-hole excitations with respect to the Hartree-Fock state. We also present a new bosonic approximation for both PBCS and QCM. In each case, the starting point is the reformulation of the pair/quartet condensate state in terms of particle-hole excitations with respect to the Hartree-Fock state. The main simplification of our approach is the assumption that the pair operators corresponding to both particle and hole states obey bosonic commutation relations. This simplifies tremendously the computations and allows for an analytic derivation of the averaged Hamiltonian on the condenstate state as a function of the mixing amplitudes. We study both the pure bosonic approach and the renormalized version, and compare the particle-hole bosonic version to the naive prescription of applying the boson approximation directly to the original condensate state. We compare the fermionic and the renormalized particle-hole bosonic approach in the case of a picket fence model of doubly degenerate states and in a realistic shell model space with an effective interaction for the $N=Z$ nuclei above $^{100}$Sn.

Magnetic excitations in La-based cuprate superconductors: Slave-boson mean-field analysis of the two-dimensionalt−Jmodel

Motivated by recent inelastic neutron scattering experiments up to a high-energy region for La-based cuprates, we compute (q,omega) maps of the imaginary part of the dynamical magnetic susceptibility chi(q,omega) in the slave-boson mean-field approximation to the two-dimensional t-J model. While the strong spectral weight appears at incommensurate positions, namely at q neq Q =(pi,pi), for low energy, the incommensurate signals disperse with increasing omega and finally merge into a commensurate signal at a particular energy omega=omega_Q. These features are seen in both the d-wave pairing state and the normal state. In particular, the incommensurate signals below omega_Q in the normal state are due to the Fermi surface geometry, which we expect for La-based cuprates because of a tendency to d-wave type Fermi surface deformations. Above omega_Q, strong signals appear to trace an upward dispersion especially for a low doping rate in the d-wave pairing state while typically broad spectral weight is obtained around q=Q in the normal state. Salient features of magnetic excitations in La-based cuprates are thus naturally captured in terms of particle-hole excitations. Global understanding of magnetic excitations in high-Tc cuprates is discussed through a comparison with magnetic excitations in YBa_2Cu_3O_y.

In-beam γ-ray spectroscopy of 56Co

Excited states of 56Co were studied in the reaction 27Al( 32S,2p1n) 56Co. The NORDBALL array with a Neutron Wall and a Silicon Ball was employed. The excited states were interpreted in terms of particle-hole excitations with respect to the doubly magic N = Z = 28 core.

Excited superdeformed band in 131Ce.

An excited superdeformed band has been observed in $^{131}\mathrm{Ce}$ consisting of 13 \ensuremath{\gamma} rays and extending to spin \ensuremath{\sim}50\ensuremath{\Elzxh}. Possible configurations are discussed in terms of particle-hole excitations in a deformed Woods-Saxon potential. \textcopyright{} 1996 The American Physical Society.

The level structure of 114Cd from (n, γ) and (d, p) studies

Gamma rays and conversion electrons have been measured following thermal neutron capture in 113Cd using the crystal spectrometers GAMS and the β-spectrometer BILL at the High Flux Reactor of the ILL at Grenoble. Primary γ-rays following thermal and average resonance neutron capture at E n = 2 keV and 24 keV were recorded at the High Flux Beam Reactor at the Brookhaven National Laboratory. The 113Cd(d, p) 114Cd reaction was studied with the Q3D spectrograph at the Munich tandem accelerator. Combining all these experimental results an almost complete level scheme of 114Cd was constructed up to 3.3 MeV including 48 excited levels with spin and parity information. The level scheme is discussed in terms of particle-hole excitations across the Z = 50 closed shell coupled to collective states, as well as in an interacting boson configuration mixing scheme.

Particle-hole excitations in 208Pb

A good description of the known collective and non-collective odd-parity levels of 208Pb may be obtained in terms of particle-hole excitations, with an interaction deduced from the spectroscopy of lighter closed shell nuclei. The random phase approximation appears to be essential for a correct prediction of transition rates; it does not require the introduction of any effective charge provided enough particle-hole configurations are included. No collective even-parity states are obtained with the model, even when 2ħω particle-hole configurations are included.