Deformations and B（E2） Values of Ne and Mg Nuclei around N = 20

The ground-state deformations and B（E2） values of Ne and Mg nuclei around N = 20 are studied within the framework of the macroscopic-microscopic （MM） model with isospin-dependent Nilsson potential. The calculated results are compared with those obtained from standard Nilsson parameters and with experimental ones. It is found that the calculations with new Nilsson parameters well reproduce the experimental large deformations and B（E2） values for Ne and Mg nuclei around N = 20. The N = 20 shell closure of Ne and Mg isotopes disappears in the MM model and this agrees with experimental data.     

Signatures of shell evolution in alpha decay across the N=126 shell closure

Within the alpha-cluster model, we particularly investigate the alpha decay of exotic nuclei in the vicinity of the N = 126 neutron shell plus the Z = 82 proton shell. The systematics of alpha-preformation probability(P_α),as an indicator of the shell effect, is deduced from the ratio of the experimental decay width to the calculated one.Through the comparative analysis of the P_α trend in the N = 124-130 isotonic chain, the N = 126 and Z = 82 shell closures are believed to strongly affect the formation of the alpha particle before its penetration. Additionally, the P_α variety in Po and Rn isotopes is presented as another proof for such an influence. More importantly, it may be concluded that the expected neutron(or proton) shell effect gradually fades away along with the increasing valence proton(or neutron) number. The odd-even staggering presented in the P_α value is also discussed.     

Triaxiality and shape coexistence in the A ～ 30 “island of inversion”nuclei

Understanding the properties of nuclei inside "island of inversion" is still an interesting issue. Based on a simple Nilsson model with a new set of isospin-dependent parameters, and with non-axial deformations considered, we have performed three-dimensional potential-energy-surface calculations for Ne, Na, Mg and Al isotopes that are claimed to be in or nearby the A～30 island of inversion". It is found that shape coexistence and triaxial deformation(or softness) exist in these nuclei. Large deformations are obtained by the improved Nilsson parameters, which explains the observed large electric quadrupole transition probabilities. The large deformations happening in30 Ne,31Na,32 Mg and33Al indicate the quenching of the spherical N = 20 neutron shell gap. The calculations of nuclear binding and two-neutron separation energies have been also improved with the isospin-dependent parameters and the inclusion of the non-axial deformation degree of freedom.     

Shell evolution in neutron-rich nuclei: the single particle perspective

The isospin dependence of spin-orbit(SO)splitting becomes increasingly important as N/Z increases in neutron-rich nuclei.Following the initial independent-particle strategy toward explaining the occurrence of magic numbers,we systematically investigated the isospin effect on the shell evolution in neutron-rich nuclei within the Woods-Saxon mean-field potential and the SO term.It is found that new magic numbers N=14 and N=16 may emerge in neutron-rich nuclei if one changes the sign of the isospin-dependent term in the SO coupling,whereas the traditional magic number,N=20,may disappear.The magic number N=28 is expected to be destroyed despite the sign choice of the isospin part in the SO splitting,corresponding to the strength of the SO coupling term.Meanwhile,the N=50 and 82 shells may persist within the single particle scheme,although there is a decreasing trend of their gaps toward extreme proton-deficient nuclei.Besides,an appreciable energy gap appears at N=32 and 34 in neutron-rich Ca isotopes.All these results are more consistent with those of the interacting shell model when enhancing the strength of the SO potential in the independent particle model.The present study may provide a more reasonable starting point than the existing one for not only the interacting shell model but also other nuclear many-body calculations toward the neutron-dripline of the Segrèchart.     

Reinvestigation of the high spin states in ^（161）Er and enhanced E1 transitions in the N=93 isotones

High-spin states in ¹⁶¹Er have been studied experimentally using the ¹⁵⁰Nd(¹⁶O, 5n) reaction at a beam energy of 86 MeV. The relatively enhanced E1 transitions between the 5/2⁺[642] and 3/2^-[521] bands are observed in ¹⁶¹Er, and the B(E1) values are extracted experimentally. The systematics of the R(E1) values in the N=93 isotones are presented. It is found that the strength of the E1 transitions obviously exhibits angular momentum dependence, and the occurrence of the relatively enhanced E1 transitions could be attributed to octupole softness.     

α particle preformation and shell effect for heavy and superheavy nuclei

The α particle preformation factor is extracted within a generalized liquid drop model for Z = 84-92 isotopes and N = 126,128,152,162,176,184 isotones.The calculated results show clearly that the shell effects play a key role in α particle preformation.The closer the proton and neutron numbers are to the magic numbers,the more difficult the formation of the α cluster inside the mother nucleus is.The preformation factors of the isotopes reflect that N = 126 is a magic number for Po,Rn,Ra,and Th isotopes,but for U isotopes the weakening of the influence of the N =126 shell closure is evident.The trend of the factors for N = 126 and N = 128 isotones also support this conclusion.We extend the calculations for N = 152,162,176,184 isotones to explore the magic numbers for heavy and superheavy nuclei,which are probably present near Z = 108 to N = 152,162 isotones and Z = 116 to N = 176,184 isotones.The results also show that another subshell closure may exist after Z = 124 in the superheavy nuclei.This is useful for future experiments.     

Nuclear structure around ~(80)Zr

Recent years have witnessed intense activity concerning the study of nuclei with equal numbers of neutrons and protons (N = Z). Exotic properties have been exhibited in the N = Z nuclei, especially in those with atomic masses around 80. In the present paper, the projected shell model(PSM)together with a relativistic Hartree-Bogoliubov (RHB) theory is used to study the nuclear structure near the N = Z line in the mass A ≈ 80 region. For three Zr isotopes 80,82,84Zr, the projected potential energy surfaces and ground state bands are calculated. It is shown that shape coexistence occurs in all of these nuclei. Moreover, we find that the residual neutron-proton interaction strongly affects the ground state band of 80Zr; however, it slightly modifies those of 82Zr and 84Zr.     

Systematic dependence of SFE*B(E2)↑ and ROTE*B(E2)↑on N_pN_n in the framework of shape fluctuation model

A systematic dependence of shape fluctuation energy product SFE * B(E2)↑ and rotational energy product ROTE * B(E2)↑ on the valence nucleon product Np Nn is carried out in the Z = 50-82,N = 82-126 major shell space.For the shape transitional nuclei,the product SFE*B(E2)↑ drops to zero and becomes negative,indicating direct dependence on N_pN_n.A relative rise,on the other hand,is observed in the product ROTE*B(E2) ↑plotted against N_pN_n for all the nuclei in Z = 50-82 and N = 82-126.In the N 104 region,large positive values of the product SFE * B(E2) ↑ are observed for the Pt nucleus,which indicates sphericity.A systematic study of the product SFE * B(E2)↑ and ROTE * B(E2) ↑ with atomic number Z is also discussed.The products SFE * B(E2) ↑and ROTE * B(E2) ↑ vary sharply with Z for the N = 88 isotones.We discuss here for the first time the correlation between SFE * B(E2) ↑ and ROTE * B(E2) ↑ with valence nucleon product N_pN_n.     

Properties and structure of N=Z nuclei within relativistic mean field theory

The axially deformed relativistic mean field theory with the force NLSH has been performed in the blocked BCS approximation to investigate the properties and structure of N=Z nuclei from Z=20 to Z=48. Some ground state quantities such as binding energies, quadrupole deformations, one/two-nucleon separation energies, root-mean-square （rms） radii of charge and neutron, and shell gaps have been calculated. The results suggest that large deformations can be found in medium-heavy nuclei with N=Z=38-42. The charge and neutron rms radii increase rapidly beyond the magic number N=Z=28 until Z=42 with increasing nucleon number, which is similar to isotope shift, yet beyond Z=42, they decrease dramatically as the structure changes greatly from Z=42 to Z=43. The evolution of shell gaps with proton number Z can be clearly observed. Besides the appearance of possible new shell closures, some conventional shell closures have been found to disappear in some region. In addition, we found that the Coulomb interaction is not strong enough to breakdown the shell structure of protons in the current region.     

Nuclear structure around 80Zr

Recent years have witnessed intense activity concerning the study of nuclei with equal numbers of neutrons and protons （N = Z）. Exotic properties have been exhibited in the N = Z nuclei, especially in those with atomic masses around 80. In the present paper, the projected shell model（PSM）together with a relativistic Hartree-Bogoliubov （RHB） theory is used to study the nuclear structure near the N = Z line in the mass A ≈ 80 region. For three Zr isotopes 80,82,84Zr, the projected potential energy surfaces and ground state bands are calculated. It is shown that shape coexistence occurs in all of these nuclei. Moreover, we find that the residual neutron-proton interaction strongly affects the ground state band of 80Zr; however, it slightly modifies those of 82Zr and 84Zr.     

A Brillouin study of the temperature-dependence of the acoustic modes across the insulator-metal transitions in V2O3 and Cr-doped V2O3

Brillouin scattering studies have been carried out on high-quality single crystals of undoped and 0.9% Cr-doped V₂O₃. The observed modes in both the samples at ∼12 and ∼60 GHz are associated with the surface Rayleigh wave (SRW) and bulk acoustic wave (BAW), respectively. In the undoped sample, the mode frequencies of the SRW and BAW modes decrease as the temperature is lowered from room temperature to the insulator-metal transition temperature (T_IM=T_N=∼130 K). Below the transition, the modes show hardening. In the doped sample, the SRW mode shows a similar temperature-dependence as the undoped one, but the BAW mode shows hardening from room temperature down to the lowest temperature (50 K). This is the first measurement of the sound velocity below T_IM in the V₂O₃ system. The softening of the SRW frequency from 330 K to T_IM can be qualitatively understood on the basis of the temperature-dependence of C₄₄, which, in turn, is related to the orbital fluctuations in the paramagnetic metallic phase. The hardening of the mode frequencies below T_IM suggests that C₄₄ must increase in the antiferromagnetic insulating phase, possibly due to the orbital ordering.     

Electronic structure of dimerized spinel ZnV2O4

Electronic structure calculations were performed for ZnV₂O₄, a material close to a metal-insulator transition. Structural optimization leads to the formation of V-V dimers along the off-plane chains. A strong spin-lattice coupling is expected close to the transition to itinerancy. No orbital ordering is observed in such a structure, and the experimentally found magnetic structure is naturally explained.     

The effect of boron on the structure and magnetic properties of Pr0.15Tb0.3Dy0.55Fe1.85 alloy

The structure, Curie temperature and magnetostriction of Pr_0.15Tb_0.3Dy_0.55Fe_1.85−xB_x   (x=0–0.3$x=0–0.3$) alloys have been investigated using X-ray diffraction, AC susceptibility and standard strain gauge techniques. It was found that all the samples possess entirely MgCu₂-type cubic Laves structure. With increasing B concentration, the lattice parameter decreases, while the Curie temperature remains unchanged. The magnetostriction of Pr_0.15Tb_0.3Dy_0.55Fe_1.85−xB_x alloys at room temperature increases with increasing B concentration firstly, and then decreases slightly.     

Isothermal equation of state for the skutterudites CoSb3 and LaFe3CoSb12

The thermoelectric materials CoSb₃ and LaFe₃CoSb₁₂ with skutterudite structure were subjected to high pressures using a diamond anvil high-pressure cell up to 20 GPa. Energy-dispersive X-ray diffraction was used to determine the dependence of the lattice parameter on pressure. No major change in the X-ray diffraction spectra was observed for both compounds, constituting evidence that both compounds are stable within this pressure range, despite their relatively open structures. Three distinct isothermal equations of state for solids under high pressure were fitted to the experimental data to determine the bulk modulus for both compounds. The filled skutterudite showed a greater compressibility than the unfilled one, this difference can be understood in terms of the larger lattice parameter of the former.     

Temperature dependence of the work function of Bi2Sr2CaCu2O8 single crystal cleaved at low temperature

We measured the anomalous change in the work function of Bi₂Sr₂CaCu₂O₈ around a critical temperature (T_c ≈ 85 K). The work function becomes a minimum at T_c; the work function decreases in a normal-conductive state and then increases in a superconductive state as the temperature decreases. An increase in the work function for a transition from a normal-conductive state to a superconductive state at 0 K is about 9 meV. The contribution of the chemical potential and the surface dipole barrier to the work function are discussed.     

High pressure electrical transport measurements of Cs2MoS4 and KTbP2Se6 and X-ray diffraction study of Cs2MoS4

We report the results of electrical resistance measurements at high pressures on Cs₂MoS₄ and KTbP₂Se₆. The results of high pressure X-ray diffraction study of Cs₂MoS₄ are also presented. Interestingly, in the case of Cs₂MoS₄ the resistance vs. pressure follows the behavior of the absorption edge vs. pressure obtained from our optical measurements lending further support to a direct-indirect band crossing. In the case of KTbP₂Se₆,the phase transition at about 9.2 GPa is reflected in a sharp drop of the resistance. In addition we report the pressure dependence of the lattice constants as well as the equation of state of Cs₂MoS₄.     

Effects of interface on the dielectric properties of Ba0.6Sr0.4TiO3 thin film capacitors

Ba_0.6Sr_0.4TiO₃ thin films were deposited on Pt/SiO₂/Si substrate by radio frequency magnetron sputtering. High-resolution transmission electron microscopy (HRTEM) observation shows that there is a transition layer at BST/Pt interface, and the layer is about 7-8 nm thickness. It is found that the transition layer was diminished to about 2-3 nm thickness by reducing the initial RF sputtering power. X-ray photoelectron spectroscopy (XPS) depth profiles show that high Ti atomic concentration results in a thick interfacial transition layer. Moreover, the symmetry ν of ?_r-V curve of BST thin film is enhanced from 52.37 to 95.98%. Meanwhile, the tunability, difference of negative and positive remanent polarization (P_r), and that of coercive field (E_C) are remarkably improved.     

Simulation of Temperature-Dependent Resistivity for Manganite La1/3Ca2/3MnO3

The resistivity of the heavy-doped La1/3Ca2/3MnO3 （LCMO） is simulated using a random resistor network model, based on a phase separation scenario. The simulated results agree well with the reported experimental data, showing a transition from a charge-disordered （CDO） state embedded with a few ferromagnetic （FM） metallic clusters to a charge-ordered （CO） state, corresponding to the transition from a high-temperature paramagnetic （PM） insulating state to a low-temperature antiferromagnetic （AF） insulating state. Furthermore, we find that the number of AF/CO clusters increases with decreasing temperature, and the clusters start to connect to each other around 250K, which causes percolating in the system. The results further verify that phase separation plays a crucial role in the electrical conductivity of LCMO.     

Intrinsic inhomogeneity and non-linear conduction in charge-ordered Bi0.5Ca0.4Sr0.1MnO3

Systematic studies of X-ray, magnetic, electronic transport, and elastic properties have been performed on polycrystalline Bi_0.5Ca_0.4Sr_0.1MnO₃ sample. The sample exhibits charge ordering (CO) state below T_CO (=304 K), accompanied by a distinct maximum in magnetization. The softening of Young's modulus in the vicinity of T_CO indicates that there is a strong coupling of electron-phonon due to Jahn-Teller (JT) effect. The dynamic ferromagnetic spin correlations are observed at high temperatures above T_CO, which are replaced by antiferromagnetic (AFM) spin fluctuations at a concomitant CO transition. Below 32 K, a spin-glass (SG) state dominates at low temperatures. The voltage-current (V-I) characteristics measurement results indicate that the non-linear conduction starts above a threshold current, giving rise to a region of negative differential resistance (NDR). The origin of the non-linear conduction is discussed in view of current induced collapse of CO state associated with phase-separation mechanism.     

μSR investigation of the magnetic ordering in EuAs3

We have investigated the magnetic ordering and the incommensurate-commensurate phase transition in EuAs₃ by zero-field (ZF) and longitudinal-field μSR. In the commensurate phase, stable at temperatures below T_L=10.3 K, the ZF muon signal exhibits oscillations corresponding to four muon precession frequencies the lowest of which behaves anomalously. The muon signal shows no oscillation but exponential decay in the incommensurate phase stable in temperature range from T_L≈10.3 K up to T_N≈11 K. The temperature dependence of the fitted relaxation rate shows divergence-like behaviour at the ordering temperature T_N≈11 K and also at the lock-in transition T_L≈10.3 K. The results are in qualitative agreement with those previously obtained by neutron and X-ray magnetic scattering investigations except for the anomalous temperature dependence of the lowest frequency in the commensurate phase. We propose a model for this anomalous behaviour.