Pairing correlations around scission

To describe pairing correlations in a fissioning system one commonly projects the BCS wave function separately onto good particle numbers in each fragment in the exit channel, but only onto the total number of particles in the parent system. We propose to interpolate between these limiting situations by the generator-coordinate method with the particle-number difference between the nascent fragments as the generator coordinate. Model calculations are presented for the Hill–Wheeler-box potential with a δ-function diaphragm to mimic scission.     

Quantum Pairing Time Orders

The concept of the time-independent correlators for the even- and odd-frequency pairing states that can be defined for both bosonic and fermionic quasiparticles is proposed. These correlators explicitly capture the existence of two distinct classes of pairing states and provide a direct probe of the hidden Berezinskii order. This concept is illustrated in the cases of pairings for Majorana fermions and quasiparticles in Dirac semimetals. It is shown that the time-independent correlator is able to effectively capture the energy scale relevant for pairing.     

Pairing Effects on Bubble Nuclei

In the framework of the Skyrme–Hartree–Fock–Bogoliubov approach with the Sk T interaction, the pairing effects on the proton bubble structures of ~(46)Ar and ~(206)Hg are discussed. In calculations, three kinds of pairing forces (volume, surface and mixed pairing interactions) are used. For ~(46)Ar, it is shown that the bubble structure with the volume pairing is almost the same as that with the mixed pairing. The bubble with the surface pairing is less pronounced than those with the volume and mixed pairings. Analyzing the density distributions and occupation probabilities of the proton s states and the quasi-degeneracy between the proton 2s_(1/2) and 1d_(3/2) orbitals, we explain the difference between the bubble structure with the surface pairing and those with the volume and mixed pairings. For ~(206)Hg, it is seen that the proton density distribution with the surface pairing is different from those with the volume and mixed pairings in the whole region of the radial distance. In addition, it is found that the bubbles with the three pairing forces are different from each other and the least pronounced bubble is obtained with the surface pairing. Thus the selection of the pairing force is important for the study of the nuclear bubble structure.     

Pairing interaction in finite Fermi-systems

The Green function method is used to treat pairing correlations in small systems. It is shown that the methods for normal systems can be used in the region of weak or medium interaction strength, provided that the energy dependent contributions to the irreducible particle-particle interaction which are necessary for the fulfilment of the Pauli-principle are not neglected. Comparisons with exact solutions and with other methods are given.     

Pairing correlations on t-U-J ladders

We find that the pairing correlations on the usual t-U Hubbard ladder are significantly enhanced by the addition of a nearest-neighbor exchange interaction J. Likewise, these correlations are also enhanced for the t-J model when the on-site Coulomb interaction is reduced from infinity. Moreover, the pairing correlations are larger on a t-U-J ladder than on a t-J(eff) ladder in which J(eff) has been adjusted so that the two models have the same spin gap at half filling. This enhancement of the pairing correlations is associated with an increase in the pair-binding energy and the pair mobility in the t-U-J model and points to the importance of the charge-transfer nature of the cuprate systems.     

Pairing effects in Sn isotopes

An extensive study of pairing effects in the Sn isotopes is carried out. The pairing Hamiltonian is treated by the chain-calculation method which provides practically exact solutions while involving less computational work than a complete-basis diagonalization. The coupling strength is fixed by reproducing the energy of the 9^? state in¹¹⁶Sn, while the single-particle energies have been determined by an analysis of the experimental low-energy spectra of the odd-A isotopes. A detailed comparison of the calculated results with experimental data evidences the importance of neutron pairing correlations in the 50–82 shell. The results of this paper complement those of our previous study of theN=82 isotones. It turns out that the role of pairing correlations is similar to a large extent in both cases.     

配对对称性与带间作用

研究d p模型的超导性质.可出现d p配对占主导的情形，配对对称性取决于CuO2面内空穴作用的各向异性，可以是纯d波配对，也可以是纯s波配对.CuO2面内各向排斥作用不能导致空穴配对.欠掺杂区域可以出现“预配对”.当库伯对是局域的则不能根据配对函数求超导临界温度.空穴的退局域以及配对参量对称性的演化也能得到理解. 关键词： d波对称性 d p配对 超导电性     

Pairing rotations and separation energies

Recent experiments exhibit a strong regularity of the two-neutron (proton) binding energies in superconducting nuclei. Using BCS calculations by Soloviev and by Kisslinger and Sorensen for the rare earth and tin region, respectively, we show that the pairing rotational model accounts for this behaviour provided the deformation does not change appreciably when two neutrons or protons are added to the system. The model relates the degree of pairing to the ground state energies of neighbouring even-even nuclei and supplements the information coming from the odd-even effect.     

An Improved Schematic Pairing Force

An improved formulation of the pairing correlation was proposed by introducing a radial correlation factor to reflect more reasonably the short range character of the correlation in nuclei.The experimental fact that the ground state band of ¹⁵⁷Tm is built on the Nilsson orbit [411]1/2⁺ is explained naturally.     

Pairing correlations in nickel isotopes

The interchange of superconducting character of protons and neutrons in going from ⁶⁰Ni to ⁶²Ni indicates that the conventional approach of assuming the pairing correlations only in neutrons with shell-closure for protons is not valid.     

Pairing symmetry of superconducting graphene

The possibility of intrinsic superconductivity in alkali-coated graphene monolayers has been recently suggested theoretically. Here, we derive the possible pairing symmetries of a carbon honeycomb lattice and discuss their phase diagram. We also evaluate the superconducting local density of states (LDOS) around an isolated impurity. This is directly related to scanning tunneling microscopy experiments, and may evidence the occurrence of unconventional superconductivity in graphene.     

Pairing in asymmetric two-component fermion matter

We analyze the possibilities of pairing between two different fermion species in asymmetric matter at low density. While the direct interaction allows pairing only for very small asymmetries, the pairing mediated by polarization effects is always possible, with a pronounced maximum at finite asymmetry. We present analytical results up to second order in the low-density parameter k_Fa.     

Pairing fluctuations in trapped fermi gases

We examine the contribution of pairing fluctuations to the superfluid order parameter for harmonically trapped atomic Fermi gases in the BCS regime. In the limit of small systems we consider, both analytically and numerically, their space and temperature dependence. We predict a parity effect, i.e., that pairing fluctuations show a maximum or a minimum at the center of the trap, depending on the value of the last occupied shell being even or odd. We propose to detect pairing fluctuations by measuring the density-density correlation function after a ballistic expansion of the gas.