Xinle Shang

Bio: Xinle Shang is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Nuclear matter & Nucleon. The author has an hindex of 6, co-authored 20 publications receiving 115 citations.

Deformed relativistic Hartree-Bogoliubov theory in continuum with a point-coupling functional: Examples of even-even Nd isotopes

Abstract: Background: The study of exotic nuclei far from the β stability line is stimulated by the development of radioactive ion beam facilities worldwide and brings opportunities and challenges to existing nuclear theories. Including self-consistently the nuclear superfluidity, deformation, and continuum effects, the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) has turned out to be successful in describing both stable and exotic nuclei. Due to several challenges, however, the DRHBc theory has only been applied to study light nuclei so far. Purpose: The aim of this work is to develop the DRHBc theory based on the point-coupling density functional and examine its possible application for all even-even nuclei in the nuclear chart by taking Nd isotopes as examples. Method: The nuclear superfluidity is taken into account via Bogoliubov transformation. Densities and potentials are expanded in terms of Legendre polynomials to include the axial deformation degrees of freedom. Sophisticated relativistic Hartree-Bogoliubov equations in coordinate space are solved in a Dirac Woods-Saxon basis to consider the continuum effects. Results: Numerical convergence for energy cutoff, angular momentum cutoff, Legendre expansion, pairing strength, and (un)constrained calculations are confirmed for the DRHBc theory from light nuclei to heavy nuclei. The ground-state properties of even-even Nd isotopes are calculated with the successful density functional PC-PK1 and compared with the spherical nuclear mass table based on the relativistic continuum Hartree-Bogoliubov (RCHB) theory as well as the available data. The calculated binding energies are in very good agreement with the existing experimental values with a rms deviation of 0.958MeV, which is remarkably smaller than 8.301MeV in the spherical case. The predicted proton and neutron drip-line nuclei for Nd isotopes are respectively Nd120 and Nd214, in contrast with Nd126 and Nd228 in the RCHB theory. The experimental quadrupole deformations and charge radii are reproduced well. An interesting decoupling between the oblate shape β2=−0.273 contributed by bound states and the nearly spherical one β2=0.047 contributed by continuum is found in Nd214. Contributions of different single-particle states to the total neutron density are investigated and an exotic neutron skin phenomenon is suggested for Nd214. The proton radioactivity beyond the proton drip line is discussed and Nd114, Nd116, and Nd118 are predicted to be candidates for two-proton or even multiproton radioactivity. Conclusions: The DRHBc theory based on the point-coupling density functional is developed and detailed numerical checks are performed. The techniques to construct the DRHBc mass table for even-even nuclei are explored and extended for all even-even nuclei in the nuclear chart by taking Nd isotopes as examples. The available experimental data are reproduced well. The deformation and continuum effects on drip-line nuclei, exotic neutron skin, and proton radioactivity are presented.

Nucleon effective mass in hot dense matter

Abstract: Nucleon effective masses are studied in the framework of the Brueckner-Hartree-Fock many-body approach at finite temperature. Self-consistent calculations using the Argonne ${V}_{18}$ interaction including a microscopic three-body force are reported for varying temperature and proton fraction up to several times the nuclear saturation density. Our calculations are based on the exact treatment of the center-of-mass momentum instead of the average-momentum approximation employed in previous works. We discuss in detail the effects of the temperature together with those of the three-body force, the density, and the isospin asymmetry. We also provide an analytical fit of the effective mass taking these dependencies into account. The temperature effects on the cooling of neutron stars are briefly discussed based on the results for $\ensuremath{\beta}$-stable matter.

Nonrelativistic nucleon effective masses in nuclear matter: Brueckner-Hartree-Fock model versus relativistic Hartree-Fock model

Abstract: The density and isospin dependencies of nonrelativistic nucleon effective mass $({m}_{N}^{*})$ are studied, which is a measure of the nonlocality of the single particle (s.p.) potential. It can be decoupled as the so-called $k$ mass (${m}_{k}^{*}$, i.e., the nonlocality in space) and $E$ mass (${m}_{E}^{*}$, i.e., the nonlocality in time). Both $k$ mass and $E$ mass are determined and compared by using the latest versions of the nonrelativistic Brueckner-Hartree-Fock (BHF) model and the relativistic Hartree-Fock (RHF) model. The latter is achieved based on the corresponding Schr\"odinger equivalent s.p. potential in a relativistic framework. We demonstrate the origins of different effective masses and discuss also their neutron-proton splitting in the asymmetric matter in different models. We find that the neutron-proton splittings of both the $k$ mass and the $E$ mass have the same asymmetry dependencies at the densities considered; namely, ${m}_{k,n}^{*}g{m}_{k,p}^{*}$ and ${m}_{E,p}^{*}g{m}_{E,n}^{*}$. However, the resulting splittings of nucleon effective masses could have different asymmetry dependencies in these two models because they could be dominated either by the $k$ mass (then we have ${m}_{n}^{*}g{m}_{p}^{*}$ in the BHF model), or by the $E$ mass (then we have ${m}_{p}^{*}g{m}_{n}^{*}$ in the RHF model). The isospin splitting in the BHF model is more consistent with the recent analysis from the nucleon-nucleus-scattering data, while the small $E$ mass ${m}_{E}^{*}$ in the RHF case as a result of the missing ladder summation finally leads to an opposite splitting behavior.

Nucleon momentum distributions in asymmetric nuclear matter

Abstract: Nucleon momentum distributions at various densities and isospin asymmetries for nuclear matter are investigated systematically within the extended Brueckner-Hartree-Fock approach. The shapes of the normalized momentum distributions varying with $k/{k}_{F}$ are practically identical, while the density- and isospin-dependent magnitude of the distribution is directly related to the depletion of the Fermi sea. Based on these properties, a parametrized formula is proposed with the parameters calibrated to the calculated result.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Dirac cone protected by non-symmorphic symmetry and three-dimensional Dirac line node in ZrSiS.

Abstract: Materials harbouring exotic quasiparticles, such as massless Dirac and Weyl fermions, have garnered much attention from physics and material science communities due to their exceptional physical properties such as ultra-high mobility and extremely large magnetoresistances. Here, we show that the highly stable, non-toxic and earth-abundant material, ZrSiS, has an electronic band structure that hosts several Dirac cones that form a Fermi surface with a diamond-shaped line of Dirac nodes. We also show that the square Si lattice in ZrSiS is an excellent template for realizing new types of two-dimensional Dirac cones recently predicted by Young and Kane. Finally, we find that the energy range of the linearly dispersed bands is as high as 2 eV above and below the Fermi level; much larger than of other known Dirac materials. This makes ZrSiS a very promising candidate to study Dirac electrons, as well as the properties of lines of Dirac nodes.

Symmetry demanded topological nodal-line materials

Abstract: The realization of Dirac and Weyl physics in solids has made topological materials one of the main focuses of condensed matter physics. Recently, the topic of topological nodal line semimetals, mat...