Search Results (15)

Nuclei are self-bound systems in which the strong interaction (nuclear force) plays a dominant role, and the isospin is approximately a good quantum number. The isospin symmetry is primarily violated by electromagnetic interactions, namely Coulomb interactions among protons, the effects of which need be studied to understand the importance of the isospin symmetry. We investigate the effect of the Coulomb interaction on nuclear properties, especially quadrupole deformation and neutron drip line, utilizing the density functional method, which provides a universal description of nuclear systems in the entire nuclear chart. We carry out calculations of even–even nuclei with a proton number of $2\le Z\le 60$. The results show that the Coulomb interaction plays a significant role in enhancing quadrupole deformation across a wide range of nuclei. We also find that, after including the Coulomb interaction, some nuclei near the neutron drip line become stable against two-neutron emissions, resulting in a shift in the drip line towards larger neutron numbers. Full article

Complex phase diagrams are a generic feature of quantum materials that display high-temperature superconductivity. In addition to d-wave superconductivity (or other unconventional states), these phase diagrams typically include various forms of charge-ordered phases, including charge-density waves and/or spin-density waves, as well as electronic nematic states. In most cases, these phases have critical temperatures comparable in magnitude to that of the superconducting state and appear in a “pseudo-gap” regime. In these systems, the high temperature state does not produce a good metal with well-defined quasiparticles but a ”strange metal”. These states typically arise from doping a strongly correlated Mott insulator. With my collaborators, I have identified these behaviors as a problem with “Intertwined Orders”. A pair-density wave is a type of superconducting state that embodies the physics of intertwined orders. Here, I discuss the phenomenology of intertwined orders and the quantum materials that are known to display these behaviors. Full article

Nuclear density functional theory (DFT) is able to reproduce the saturation properties of nuclear matter, as well as properties of finite nuclei. Consequently, the DFT calculations are applicable to nuclei across a wide range of masses on the nuclear chart. The Gogny-type density functional, which is equivalent to the mean-field calculations with finite-range density-dependent effective interactions, is a successful example. In contrast, the shell model (configuration interaction) calculation is a powerful tool to describe nuclear structure, especially spectroscopic properties. The shell model is able to take into account correlations beyond mean-field in a truncated model space. In this work, we report an investigation on $sd$-shell nuclei and Ca isotopes using a hybrid approach of the shell model and Gogny-type DFT. Full article

This study investigates the masses and quadrupole deformations of even-Z nuclei within the range $8⩽Z⩽104$ using the triaxial relativistic Hartree–Bogoliubov model (TRHB) with the PC-PK1 density functional. For odd-mass nuclei, the global minima were determined using the automatic blocking method and their dynamical correlation energies (DCEs) were approximated using the average values of neighboring even–even nuclei calculated from a microscopic, five-dimensional, collective Hamiltonian (5DCH). The mean-field results underestimate the binding energies of most open-shell nuclei, with an initial root–mean–square (rms) deviation of 2.56 MeV for 1223 even-Z nuclei. Incorporating DCEs significantly reduces this deviation to 1.36 MeV. Additionally, the descriptions of two-neutron and one-neutron separation energies are improved, with rms deviations decreasing to 0.75 MeV and 0.65 MeV, respectively. Further refinement through accounting for odd–even differences in DCEs reduces the rms deviations for binding energies and one-neutron separation energies to 1.30 MeV and 0.63 MeV, respectively. Regarding the quadrupole deformations, TRHB calculations reveal spherical shapes near shell and subshell closures, well-deformed shapes at the mid-shell, and rapid shape transitions in medium- and heavy-mass regions. Oblate shapes dominate in regions $(Z,N)\sim (14,14),(34,36)$, and $(40,60)$, and the neutron-deficient Pb region, with notable odd–even shape staggering attributed to the blocking effect of the odd nucleon. Triaxial shapes are favored in the mass regions $(Z,N)\sim (60,76)$ and $(76,116)$. Full article

We investigated the reaction Q-value ($Q_{\alpha }$) for the $\alpha$ decay of Tl, Bi, and At isotopes using the deformed relativistic Hartree–Bogoliubov theory in continuum (DRHBc) with the covariant density functional PC-PK1. The $\alpha$ decay half-lives of Tl, Bi, and At isotopes are evaluated using various empirical formulas, based on both experimental $Q_{\alpha }$ and those obtained from DRHBc calculations. The calculated $Q_{\alpha }$ and $\alpha$ decay half-lives are compared with experimental data. On the basis of these results, we also predicted the $\alpha$ decay half-lives of isotopes for which experimental data are unavailable. Full article

Bubble nuclei, characterized by a depletion in nucleon density at the nuclear center, are investigated within the atomic number range $71\le Z\le 80$ using the Deformed Relativistic Hartree–Bogoliubov theory in continuum. This study extends previous investigations, which were limited to even–even isotopes, by incorporating even–odd, odd–even, and odd–odd nuclei within this range. The extension is achieved by introducing the blocking effect into the point-coupling approach to ensure self-consistency. Following previous studies, we define a nucleus as a bubble candidate if the bubble parameter exceeds ${\mathcal{B}}_p^{★}=20\%$, and identify five bubble nuclei in both even-Z and odd-Z nuclei groups, based on the highest ${\mathcal{B}}_p^{★}$ values. The formation of bubble structures is confirmed through an analysis of proton single-particle energy levels of the most centrally depleted nuclei across four categories: even–odd, even–even, odd–even, and odd–odd. Full article

The shape of a nucleus is one of its fundamental properties. We conduct a systematic investigation of shape coexistence in odd-Z nuclei from fluorine to potassium using the deformed relativistic Hartree–Bogoliubov theory in continuum. First, we present a simple argument regarding the energy differences between degenerate vacua, which can serve as a criterion for identifying candidates for shape coexistence. We then predict isotopes that exhibit shape coexistence. Full article

By adopting the deformed relativistic Hartree–Bogoliubov theory in continuum (DRHBc) with the point-coupling density functional PC-PK1, we investigate the shell structure evolution of even–even U, Pu, and Cm isotopic chains from the proton drip line to the neutron drip line. The Fermi energy ${\lambda }_n$, two-neutron separation energy $S_{2\mathrm{n}}$, two-neutron shell gap ${\delta }_{2\mathrm{n}}$, and quadrupole deformation ${\beta }_2$ all indicate the major shell closures at N = 126, 184, and 258. The emergence of sudden drops between U and Pu isotopic chains in the proton Fermi energies ${\lambda }_p$ around these neutron shell closures is a consequence of the designation convention when the pairing collapse at the spurious shell closure Z = 92 occurs. The fine structure in the two-neutron shell gap, like negative ${\delta }_{2\mathrm{n}}$, may be related to the ground-state shape transition. Finally, the subshells indicated by the small-scale peaks in the two-neutron shell gaps can be well understood by the deformed gaps in the single-neutron levels obtained by DRHBc theory. Full article

I propose a data-driven surrogate model for the In-Medium Similarity Renormalization Group (IMSRG) method using Dynamic Mode Decomposition (DMD). First, the Magnus formulation of the IMSRG is leveraged to represent the unitary transformation of many-body operators of interest. Then, snapshots of these operators at different flow parameters are decomposed by DMD to approximate the IMSRG flow in a latent space. The resulting emulator accurately reproduces the asymptotic flow behavior while lowering computational costs. I demonstrate that the DMD-based emulator results in a three to five times speedup compared to the full IMSRG calculation in a few test cases based on the ground state properties of ⁵⁶Ni, ¹⁶O, and ⁴⁰Ca in realistic nuclear interactions. While this is still not an acceleration that is significant enough to enable us to fully quantify, e.g., statistical uncertainties using Bayesian methods, this work offers a starting point for constructing efficient surrogate models for the IMSRG. Full article

Two extensions of the variational method with explicit energy functionals (EEFs) with respect to the spin-orbit force were performed. In this method, the energy per nucleon of nuclear matter is explicitly expressed as a functional of various two-body distribution functions, starting from realistic nuclear forces. The energy was then minimized by solving the Euler–Lagrange equation for the distribution functions derived from the EEF. In the first extension, an EEF of symmetric nuclear matter at zero temperature was constructed using the two-body central, tensor, and spin-orbit nuclear forces. The energy per nucleon calculated using the Argonne v8’ two-body nuclear potential was found to be lower than those calculated using other many-body methods, implying that the energy contribution caused by the spin-orbit correlation, whose relative orbital angular momentum operator acts on other correlations, is necessary. In a subsequent extension, the EEF of neutron matter at zero temperature, including the spin-orbit force, was extended to neutron matter at finite temperatures using the method by Schmidt and Pandharipande. The thermodynamic quantities of neutron matter calculated using the Argonne v8’ nuclear potential were found to be reasonable and self-consistent. Full article

Whether $Z=126$ is a proton magic number has been controversial in nuclear physics. The even-even ${}_{126}\mathrm{Ubh}$ isotopes are calculated based on the DRHBc calculations with PC-PK1. The evolutions of quadrupole deformation and pairing energies for neutron and proton are analyzed to study the possible nuclear magicity. Spherical shape occurs and neutron pairing energy vanishes at $N=258$ and 350, which are the results of possible neutron magicity, while the proton pairing energy never vanishes in Ubh isotopes, which does not support the proton magicity at $Z=126$. In the single-proton spectrum, there is no discernible gap at $Z=126$, while significant gaps appear at $Z=120$ and 138. Therefore, $Z=126$ is not supported as a proton magic number, while $Z=120$ and 138 are suggested as candidates of proton magic numbers. Full article

The deformed relativistic Hartree–Bogoliubov theory in continuum (DRHBc) has garnered significant attention for its ability to describe the properties of nuclei across the entire nuclear chart, from light to heavy nuclei, including both stable and exotic ones. As part of ongoing efforts to construct a mass table using the DRHBc theory, determining the ground states of nuclei is a crucial task in the systematic studies of deformed nuclei. In this work, a strategy for identifying the ground state in the superheavy nuclei region is proposed and evaluated, by taking $Z=134$ and 135 isotopes as examples. First, we examine how the step size of the initial quadrupole deformation parameter, $\Delta {\beta }_2$, affects the pattern of the potential energy curves (PECs) and the determination of the ground state. Our findings indicate that $\Delta {\beta }_2=0.05$ producing smooth and well-defined PECs while maintaining an acceptable numerical cost. Next, we explore the convergence of PECs with respect to the angular momentum cutoff, $J_{\max }$. Based on the results, we recommend using $J_{\max }=31/2\hslash$, especially for nuclei with competing oblate and prolate minima. Finally, we conclude that the accurate identification of the ground state can be achieved by performing unconstrained calculations around the minima of the PECs. Full article

The impact of the Lipkin–Nogami (LN) method on a giant halo is investigated within the relativistic continuum Hartree–Bogoliubov (RCHB) theory. The ground-state properties of Ca isotopes obtained from RCHB and RCHB+LN calculations are presented. The results show that the LN correction does not change the range of Ca isotopes with a giant halo. Taking ⁶⁶Ca as an example, the neutron density distribution with LN correction is found to be slightly more diffused, which can be illustrated by the enlargement of the root mean square radius and the enhancement of the relative contribution in neutron $3s_{1/2}$ level. Full article

In the framework of axial symmetric relativistic Hartree–Bogoliubov (RHB) theory and the Skyrme Hartree–Fock–Bogoliubov (HFB) theory, the evolution of shell structure, density distribution, and ground state deformation in superheavy nuclei proximate to $N=258$ are investigated within the relativistic functionals DD-PC1 and DD-ME2, as well as the non-relativistic functional UNEDF0. The results from DD-ME2 and UNEDF0 indicate that $N=258$ is a neutron magic number, whereas DD-PC1 does not anticipate the existence of a bound $N=258$ magic nucleus. Further discussion suggests that the emergence of the magic number $N=258$ is related to the depression of the central density. Full article

The investigation of magic numbers for nuclei in the hyperheavy region $(Z>120)$ is an interesting topic. The neutron magic number $N=350$ is carefully validated by the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc), via analysing even-even nuclei around $N=350$ of the $Z=136$ isotopes in detail. Nuclei with $Z=136$ and $340\le N\le 360$ are all found to be spherical in their ground states. A big drop of the two-neutron separation energy $S_{2n}$ is observed from $N=350$ to $N=352$ in the isotopic chain of $Z=136$, and a peak of the two-neutron gap ${\delta }_{2n}$ appears at $N=350$. There exists a big shell gap above $N=350$ around the spherical regions of single-neutron levels for nucleus with $(Z=136,N=350)$. These evidences from the DRHBc theory support $N=350$ to be a neutron magic number in the hyperheavy region. Full article