Shape-induced phase transition of vortex domain structures in ferroelectric nanodots and their controllability by electrical and mechanical loads

Shape-induced phase transition of vortex domain structures （VDSs） in BaTiO3 （BT） nanodots under open circuit boundary condition have been investigated using an effective Hamiltonian method. Our calculation indicates the tetragonal VDS missing in cubic BT nanodots can be induced by varying the shape of a nanodot from cube to platelet. Interestingly, a novel VDS is found in BT nanoplatelets in our simulations. Further investigation shows that it is a result of compromise between the ground state and the symmetry of the shape of the nanodot. Furthermore, based on the novel VDS, routes of controlling VDSs governed by homogeneous electric field and uniform stress are discussed. In particular, our results show the possibility of designing multi-states devices based on a single VDS. ~ 2017 The Authors. Published by Elsevier Ltd on behalf of The Chinese Society of Theoretical and Applied Mechanics.

Effects of single particle on shape phase transitions and phase coexistence in odd-even nuclei

A classical analysis of shape phase transitions and phase coexistence in odd-even nuclei has been performed in the framework of the interacting boson-fermion model. The results indicate that the effects of a single particle may influence different types of transitions in different ways. Especially, it is revealed that phase coexistence can clearly emerge in the critical region and thus be taken as a indicator of the shape phase transitions in odd-even nuclei.

Effects of an odd particle on shape phase transitions in odd-even systems

A scheme to solve the Hamiltonian in the interacting boson-fermion model in terms of the SU(3)coupling basis is introduced,through which the effects of an odd particle on shape phase transitions(SPTs)in odd-A nuclei are examined by comparing the critical behaviors of some selected quantities in odd-even and even-even systems.The results indicate that the spherical to prolate(U(5)-SU(3))SPT and spherical to γ-soft (U(5)-O(6))SPT may clearly occur in the odd-even system with the SPT signatures revealed by various quantities including the excitation energies,energy ratio,B(E2)ratio,quadrupole moments,and one-particle-transfer spectroscopic intensities.In particular,the results indicate that the spherical to prolate SPT in the odd-even system can even be strengthened by the effects of the odd particle with the large fluctuations of the quadrupole deformations appearing near the critical point.

Shape phase transition in neutron-rich even-even light nuclei with Z=20-28

The E-Gamma Over Spin （E-GOS） analysis method is applied to the study of the shape phase transition of neutron-rich even-even light nuclei with Z=20-28. Some valuable results are gained through analysing E-GOS curves of Ca, Ti, Cr, Fe and Ni nuclei.

Shape phase transition in the odd Sm nuclei: effective order parameter and odd–even effect

Some binding energy related quantities serving as effective order parameters have been used to analyze the shape phase transition in the odd Sm nuclei. It is found that the signals of phase transition in the odd Sm nuclei are greatly enhanced in contrast to the even Sm nuclei. A further analysis shows that the transitional behaviors related to pairing in the Sm nuclei can be well described by the mean field plus pairing interaction model, with a monotonic decrease in the pairing strength G.

Shape coexistence close to N=50 in the neutron-rich isotope ^(80)Ge investigated by IBM-2

The properties of the low-lying states especially the relevant shape coexistence in 80Ge, close to one of most neutron-rich doubly magic nuclei at N 50 and Z = 28, have been investigated within the framework of the proton-neutron interacting model （IBM-2）. Based on the fact that the relative energy of the d neutron boson is different from that of the proton boson, the calculated energy levels of low-lying states and E2 transition strengths can reproduce the experimental data very well. Particularly, the first excited state 0＋, which is intimately related to the shape coexistence phenomenon, is reproduced quite nicely. The p2（E0,02＋→01＋） transition strength is also predicted. The experimental data and theoretical results indicate that both collective spherical and γ-soft vibration structures coexist in 80Ge.

Local variations of charge radii for nuclei with even Z from 84 to 120

Pronounced changes of nuclear charge radii provide a stringent benchmark on the theoretical models and play a vital role in recognizing various nuclear phenomena.In this work,the systematic evolutions of nuclear charge radii along even Z=84-120 isotopic chains are first investigated by the recently developed new ansatz under the covariant density functional.The calculated results show that the shell closure effects of nuclear charge radii appear remarkably at the neutron numbers N=126 and 184.Interestingly,the arch-like shapes of charge radii between these two strong neutron-closed shells are naturally observed.Across the N=184 shell closure,the abrupt increase in charge radii is still evidently emerged.In addition,the rapid raise of nuclear charge radii from the neutron numbers N=138 to N=144 is disclosed clearly in superheavy regions due to the enhanced shape deformation.

Structure Evolution in the Even-Even ^124-134Xe with IBM2

We have investigated the structure evolution of the ^124-134Xe isotopic chain in the framework of the proton-neutron interacting model IBM2. The positive parity spectra of the ground state, quasi-β and quasi-γ bands are reproduced well. The staggering in ^124-130Xe are almost completely removed and the ？ band agree well with the experiment data, even for the high-spin quasi-3 states. The key quantities of the collective structure evolution, including level energies, the B（E2） transition branching ratios, and the M1 excitations to 11^＋ mixer-symmetry states are analyzed by comparing with the experimental data. The parameters for representation of the Oπν（6） and SUπν^＊（3） features in isotopes are examined. Both experimental data and theoretical results show that the shape phase transition of ^124-134Xe isotopic chain is from the SUπν^＊ （3） （triaxial rotation） to the Uπν（5） （vibration motion） with a considerable constituent of the Oπν（6） symmetry （γ-unstable rotation）, where the shape phase transition rapidly takes place between the neutron number N = 76 and N = 78.