Phase Transitions and Shape Coexistence in Atomic Nuclei

Physics of Atomic Nuclei - Examples of phase transitions occurring in atomic nuclei in response to an increase in the excitation energy and angular momenta and in response to a change in the number...     

Shape Coexistence in Odd-Mass Nuclei near Z = 50

An earlier work dealing with shape coexistence for even-even nuclei is extended to treating odd-mass nuclei including proton excitations across closed shell. With the approach, energy spectra and some E2 transition branching ratios are calculated for odd-Anuclei^113~125Sb,^115~127I. The theoretical results give a good reproduction to the experimental data.     

原子核过渡区的量子相变

在相互作用玻色子模型(IBM) 基础上用O(6) 高阶项代替传统的SU(3) 四极-四极相互作用来研究原子核从振动到转动过渡区的量子相变行为。利用U(5)-SU(3) 和UQ 两种方案,在玻色子数分别为N = 8 和N = 20 不同情况下,研究了原子核的一些低激发态的能级比和电四极跃迁比。结果表明:随着玻色子数N 的增大,系统的量子相变行为得到加强;两种方案都可以用来描述从振动到转动过渡区的原子核的量子相变特征且O(6) 高阶项方案下量子相变行为更为明显。在此基础上,进一步应用这两种方案具体讨论了152Sm 核的低激发态能级和电四极跃迁性质并与实验数据进行对比分析。结果表明,用O(6) 高阶项可以更为合理地描述带内跃迁及不同带之间的带间跃迁性质。With the framework of Interacting Boson Model(IBM), transitional patterns from the spherical to the axially deformed limit of the IBM with a schematic Hamiltonian are studied by replacing the SU(3) quadrupole-quadrupole term with O(6) cubic interaction. But, we use the two schemes to investigate some energy ratios and B(E2) ratios for different bosons N = 8 and N = 20. The results show that with the increasing of the numbers of bosons, the transitional behaviors can be enhanced; the transitional behaviors are very similar in the two schemes. However, there are some distinctive differences for some quantities across the entire transitional region, such as energy levels and ratios, B(E2) values and ratios, and expectation values of the shape variables. Generally speaking, the transition is smoother and the nuclear shape is less well defined in the new scheme. Then we apply the two schemes to the critical point symmetry candidate, such as 152Sm, and find the overall fitting quality of the UQ scheme is better than that of the U(5)-SU(3) scheme, especially for the inter-band E2 transitions in 152Sm.     

NMR Line Shape for a Rectangular Configuration of Nuclei

We present an approach to describe nuclear magnetic resonance absorption of dipolar-coupled rectangular configuration of nuclear spins associated with reorientation of ethylene bridge (–CH₂–CH₂–) in the crystal. The approach was applied to investigate reorientational mobility of dabco-linkers (1,4-diazobycyclo[2,2,2]octane) in metal–organic framework [Zn₂(bdc)₂(dabco)] (bdc—benzenedicarboxylate). Dabco rotation around the N–N axis is shown to remain down to 80 K and the activation energy of the molecule reorientation does not exceed 12 kJ/mol.     

原子核液气相变的动力学研究

应用量子分子动力学模型,从原子核发生碎化时的碎块质量分布、密度涨落以及混沌动力学中描述混沌程度的最大Lyapunov指数等3个方面,对原子核的液气相变及其在临界点附近的行为进行较为全面的探讨.通过研究,发现在临界温度附近原子核发生最大的液气共存、密度涨落达到极大以及产生最大混沌构型.     

Berry几何相与量子跃迁

针对Berry几何相的出现所关联的量子能级,微弱变化跃迁的物理背景条件进行分析研究;对严格产生(获得)Berry几何相与这种微弱变化跃迁之间的内在关系作进一步探讨.结果表明:Berry几何相的严格产生都是由系统在演变过程中所出现的量子能级微弱变化跃迁的绝热极限效应所必然导致的结果.     

原子核有序到混沌相变与大变形的稳定性

从原子核有序到混沌相变的观点讨论原子核大变形的稳定性，从而对核裂变和某些核结构问题以新的理解． The Stability of a large deformed configuration of nuclei has been discussed from the point of view of interplay between order and chaos. A further understanding of fission dynamic and some problems on nuclear structure have been obtained.     

Chirality Quantum Phase Transition in Noncommutative Dirac Oscillator

The charged Dirac oscillator on a noncommutative plane coupling to a uniform perpendicular magnetic field is studied in this paper. We map the noncommutative plane to a commutative one by means of Bopp shift and study this problem on the commutative plane. We find that this model can be mapped onto a quantum optics model which contains Anti-Jaynes-Cummings (AJC) or Jaynes-Cummings (JC) interactions when a dimensionless parameter ζ (which is the function of the intensity of the magnetic field) takes values in different regimes. Furthermore, this model behaves as experiencing a chirality quantum phase transition when the dimensionless parameter ζ approaches the critical point. Several evidences of the chirality quantum phase transition are presented. We also study the non-relativistic limit of this model and find that a similar chirality quantum phase transition takes place in its non-relativistic limit.     

Coherence and Quantum Phase Transition in Spin Models

Based on quantum renormalization group (QRG) method, we investigated quantum coherence and quantum phase transition (QPT) in XXZ chain and XY chain, respectively. The results show that both the geometric quantum coherence and entropic coherecne can accurately indicate the QPT at critical point after enough iteration steps. Moreover, the increasing anisotropy parameter destroys the coherence in the XXZ chain, while enhances it in the XY chain. In addition, focused on the XXZ chain we analyzed the nonanalytic phenomena and scaling behaviors with different theoretical exponents in detail.

     

双层Heisenberg反铁磁体中的量子相变

用键算符平均场方法研究了双层正方格子Heisenberg反铁磁体中的量子相变问题.得到的临界点以及低温下的量子临界行为符合相关的数值计算结果和非线性σ模型的结果.在数值计算不能达到的极低温度范围（T≤0.3J₁,J₁为面内最近邻反铁磁交换作用）,给出了量子临界行为的新证据. 关键词：     

核物质液-气相变和热核稳定性

简述了研究核物质液－气相变的理论计算及研究热核稳定性的二相平衡模型．讨论了相变的临界温度及其对核物质大小、不对称度及库仑相互作用的依赖性．比较了用各种核力或模型算得的热核极限温度及实验结果． A brief introduction of the theoretical studies of liquid gas phase transition in nuclear matter and a two phase equilibrium model for studying stability of hot nuclei is presented. The critical temperature of the phase transition and its dependence on size and asymmetry of nuclear matter and Coulomb interaction are discussed. The limiting temperatures of hot nuclei calculated with various nuclear forces or models and experimental results are compared.     

On the Liguid-Gas Phase Transition and the Instability of Hot Nuclei

Based on a simple semi-empirical energy density, the free energy density for a hot nucleon system is derived, from which the equations of state P(T, p) and chemical potentials μ_q(T, p) for both finite nucleus and infinite nuclear matter are acquired. The liquid-gas phase transition and the instability of hot nuclei are analysed with these ingredients within the framework of thermodynamic's. Both critical temperature T_c for infinite nuclear matter and limiting temperature T_lim, for finite nuclei are predicted and compared with previous calculations.     

Quantum Phase Transition and Ferromagnetic Spin Correlation in Parallel Double Quantum Dots

We investigate electronic transport through a parallel double quantum dot （DQD） system with strong on-site Coulomb interaction, as well as the interdot tunnelling. By applying numerical renormalization group method, the ground state of the system and the transmission probability at zero temperature are obtained. For a system of quantum dots with degenerate energy levels and small interdot tunnel coupling, the spin correlations between the DQDs is ferromagnetic, and the ground state of the system is a spin-1 triplet state. The linear conductance will reach the unitary limit （2e^2/h） due to the Kondo effect at low temperature. As the interdot tunnel coupling increases, there is a quantum phase transition from ferromagnetic to anti-ferromagnetic spin correlation in DQDs and the linear conductance is strongly suppressed.     

Quantum Dissonance as an Indicator of Quantum Phase Transition in the XXZ Chain

We investigate the behavior of quantum dissonance in the anti-ferromagnetic XXZ spin S = 1/2 chain, which exhibits a quantum phase transition. Based on a unified view of quantum and classical correlations, quantum dissonance is analytically calculated and is compared with entanglement, discord, and classical correlations for the ground state of the system. It is found that the nearest-neighbor quantum dissonance achieves an extremum and exhibits the sharpest change at the critical point. Therefore, quantum dissonance may serve as a more efficient indicator of quantum phase transitions in the XXZ spin chain.     

Einstein-Podolsky-Rosen Steering and Quantum Phase Transition in Spin Chains

We study the Einstein-Podolsky-Rosen steering and quantum phase transitions of the transverse Ising and antiferromagnetic XXZ spin-1/2 chains. By making use of steerable weight, we calculate the steerability for the bipartite subsystems of the models. It is shown that steerability vanishes abruptly and its value maintains zero in a region close to the critical point for the Ising chain. This result is quite different from the information provided by entanglement and quantum discord. While for the XXZ chain, steerability increases and reaches maximal at the critical point, indicating the occurrence of quantum phase transition.     

Existence of a Phase Transition in a Continuous Quantum System

We prove the existence of a phase transition in the quantum Widom–Rowlison model in two dimension. The case of Boltzmann and Bose statistics are explicitly discussed.     

Quantum Phase Transition in Two Species of Cold Bosonic Atoms

In this letter,the superfluid-Mott-insulator phase transition of two-species cold bosonic atoms in an optical lattices is studied.The Hamiltonian of this model is diagonalized by means of Bogliubov transformations and by the inversion symmetry of the optical lattice,the energy spectrum of this system is obtained.From the energy gap of the excitation spectrum,the quantum phase transition condition is obtained and it is determined by the competition between the interatomic repulsions and the tunnel coupling.It is found that there exists an ordinary fluid phase when taking the zero wave-vector limit.     

Interferometry Signatures for QCD First-Order Phase Transition in High Energy Heavy Ion Collisions

Using the technique of quantum transport of the interfering pair we examine the Hanbury-Brown-Twiss （HBT） interferometry signatures for the particle-emitting sources of pions and kaons produced in heavy ion collisions at 10-30 AGeV. The evolution of the sources is described by relativistic hydrodynamics with the first-order phase transition from quark-gluon plasma （QGP） to hadronic matter. We use quantum probability amplitudes in a path-integral formalism to calculate the two-particle correlation functions, where the effects of particle decay and multiple scattering are taken into consideration. Our model-calculated results indicate that both the HBT radii of pions and kaons increase with the system initial energy density. The HBT lifetimes of the pion and kaon sources increase significantly when the initial energy density is tuned to the phase boundary between the QGP and mixed phase. This increase of HBT lifetimes will likely appear in heavy ion collisions with an incident energy between 10-30 AGeV.     

Shape Coexistence in 74Se

The 0 _1,2 ⁺ ,2 _1,2 ⁺ and 4 _1,2 ⁺ states in ⁷⁴Se have been described as linear combinations of pure states with definite deformation within a two-band mixing model. The mixing amplitudes between the spherical and deformed configurations and the mixing matrix elements have then been extracted from the calculations. The exchanged position between the spherical and deformed configurations at I=4 has been obtained within this model.