载流子在金属/聚对苯乙炔/金属结构中注入及输运的动力学研究

采用紧束缚的Su-Schrieffer-Heeger模型,利用非绝热动力学方法研究了载流子在金属/聚对苯乙炔(poly(p-phenylene vinylene,简记为PPV))/金属三明治结构中注入与输运的动力学过程.发现由于强的电子-晶格相互作用,注入的电荷在PPV链中形成波包,波包的形成与施加在金属电极上的偏压、PPV链上的电场强度及金属电极与PPV之间的界面耦合强度密切相关.在无外电场的情况下,当偏压达到临界值时电荷能够从金属电极注入到PPV链中并形成波包.随着电场强度的增大,波包能 关键词： 金属/聚对苯乙炔/金属结构 载流子输运 波包     

Electrical properties and memory effect in the field effect transistor based on organic ferroelectric insulator and pentacene

We have fabricated a field effect transistor (FET) based on an organic ferroelectric insulator and molecular conductor, and investigated the electrical properties and memory effects on the PEN-FET. We have observed a drastic change in the drain current at around the coercive electric fieldE _c of the organic ferroelectric insulator in not only a FET (PEN-FET) based on a pentacene (PEN) film but also a FET (IPEN-FET) based on an iodine doped PEN film. The magnitude of the change of the drain current for the IPEN-FET is 200 times larger than that for the PEN-FET. It is expected from these results that the PEN-FET (especially the IPEN-FET) is an improvement in such devices, since it operates at a low gate electric field accompanied by the appearance of the spontaneous polarization in the organic ferroelectric insulator. In addition, we have found that the drain current for the PEN-FET does not return to the initial drain current ofE _G =0 V/cm for more than one week, even if the gate electric field is changed to 0 V/cm from 500 V/cm(>E _c ). From these results, it is suggested that the PEN-FET becomes a memory device.     

Wess–Zumino Currents on S3 × R Spacetime

Based on the group theory powerful techniques, as a rigorous tool for treating fields on S ³ × R spacetime, which is the manifold of SU(2), we put the supersymmetric Wess–Zumino model on the S ³ × R background. After deriving the system of Klein–Gordon–Dirac-type equations, for the scalar and Majorana fields, we get in the corresponding current, besides the supercurrent, an additional term due to the coupling of spin to gravity. Finally, considerations on the solutions of the fields equations are made, pointing out significant differences from the Minkowskian case.     

Franz–Keldysh oscillations at the miniband edge in a GaAs/AlxGa1 −xAs superlattice

We have systematically measured the electroreflectance spectra of a GaAs (7.0 nm)/Al_0.1Ga_0.9As (3.5 nm) superlattice at various electric fields to investigate Franz–Keldysh (FK) oscillations. In the low-field regime, we clearly observe the FK oscillations toward the low-energy side of theM₁critical point (mini-Brillouin-zone edge). As the electric field is increased, the direction of the FK oscillations is reversed, then the oscillations disappear. The change of the oscillation direction correlates with the transformation of the electronic structures from the miniband to the Stark-ladder states in the Wannier-Stark localization. We discuss these experimental results on the basis of a theory of the FK oscillations and envelope-function forms calculated by a transfer matrix method with Airy functions.     

单磁场驱动的Tb1-xDyxFe2-y/Pb(Zr,Ti)O3三层膜磁电效应

研究了Tb_1-xDy_xFe_2－y (TDF)与锆钛酸铅(PZT)三层膜样品的制备和在单一直流磁场驱动下的磁电(ME)效应. 在该系列三层膜样品中测量到了巨大的ME耦合效应. 所得实验结果与同种样品在两磁场驱动下的ME效应完全不同. 这可能预示了某些新的物理内容. 该技术可简化ME效应在某些实际应用中的复杂度. 关键词： 1-xDy_xFe_2－y')" href="#">Tb_1-xDy_xFe_2－y PZT 单磁场 ME效应     

Evolution of emergent C-points, L-lines, and C-lines in free space

Polarization singularities,which emerge from the incoherent superposition of two vector electric fields with the same frequency,and their evolution in free space are studied analytically and illustrated by numerical examples.It is shown that there exist C-points,L-lines,in particular,C-lines in incoherently superimposed two-dimensional wavefields.Usually,the C-lines are unstable and disappear during the free-space propagation.The motion,pair creation-annihilation process of the emergent C-points,as well as the distortion of the L-lines may take place,and the degree of polarization of the emergent C-points varies upon propagation and may be less than 1.     

Runaway of electrons in dense gases and mechanism of generation of high-power subnanosecond beams

New understanding of mechanism of the runaway electrons beam generation in gases is presented. It is shown that the Townsend mechanism of the avalanche electron multiplication is valid even for the strong electric fields when the electron ionization friction on gas may be neglected. A non-local criterion for a runaway electron generation is proposed. This criterion results in the universal two-valued dependence of critical voltage U _cr on pd for a certain gas (p is a pressure, d is an interelectrode distance). This dependence subdivides a plane (U _cr , pd) onto the area of the efficient electron multiplication and the area where the electrons leave the gas gap without multiplication. On the basis of this dependence analogs of Paschen’s curves are constructed, which contain an additional new upper branch. This brunch demarcates the area of discharge and the area of e-beam. The mechanism of the formation of the recently created atomospheric pressure subnanosecond e-beams is discussed. It is shown that the beam of the runaway electrons is formed at an instant when the plasma of the discharge gap approaches to the runaway electrons is formed at an instant when the plasma of the discharge gap approaches to the anode. In this case a basic pulse of the electron beam is formed according to the non-local criterion of the runaway electrons generation. The role of the discharge gap preionization by the fast electrons, emitted from the plasma non-uniformities on the cathode, as well as a propagation of an electron multiplication wave from cathode to anode in a dense gas are considered.     

Magnetic phases in UNi<Subscript>2</Subscript>Si<Subscript>2</Subscript>

The tetragonal compound UNi₂Si₂ exhibits in zero magnetic field three different antiferromagnetic phases belowT _N =124 K. They are formed by ferromagnetic basal planes, which are antiferromagnetically coupled along thec-axis with the propagation vectorq=(0, 0, q _z ). Two additional order-order magnetic phase transitions are observed below T _N , namely atT ₁=108 K and T ₂=40 K in zero magnetic field. All three phases exhibit strong uniaxial anisotropy confining the U moments to a direction parallel to the c-axis. UNi₂Si₂ single crystals were studied in detail by measuring bulk thermodynamic properties, such as thermal expansion, resistivity, susceptibility, and specific heat. A microscopic study using neutron diffraction was performed in magnetic fields up to 14.5 T parallel to the c-axis, and a complex magnetic phase diagram has been determined. Here, we present the analysis of specific-heat data measured in magnetic fields up to 14 T compared with the results of the neutron-diffraction study and with other thermodynamic properties of UNi₂Si₂.     

Magnetotransport and magnetotunneling in single-layer, two-layer, and three-layer Bi2Sr2Can−1CunOz (n=1,2,3) single crystals

In continuous magnetic fields H up to 28 T, we have studied the out-of-plane transport properties and tunneling characteristics of high-quality nondoped single crystals of the Bi-cuprate family: Bi₂Sr₂CuO_6+δ (Bi2201), Bi₂Sr₂CaCu₂O_8+δ (Bi2212) and Bi₂Sr₂Ca₂Cu₃O_10+δ (Bi2223) grown by an identical method. For all compounds the out-of-plane magnetotransport ρ_c(H) is negative in the temperature region where ρ_c(T) shows in the normal state a semiconducting-like temperature dependence. The negative magnetoresistance of ρ_c corresponds to the suppression of the semiconducting temperature dependence of ρ_c(T) which is found to be isotropic. For the Bi2201 compound, where the normal state can be reached in the available magnetic fields (28 T), a nearly complete suppression of the low-temperature upturn in ρ_c(T) is observed in the highest magnetic fields with a tendency towards a metallic behavior down to the lowest temperatures (0.4 K). Using the break-junction technique, especially for the Bi2212 and Bi2232 compounds, a clear superconducting gap structure can be observed. Both for temperatures above the critical temperature and for magnetic fields above the upper critical field, a pseudogap structure remains present in the tunneling spectra. The applied magnetic fields yield a stronger suppression of the superconducting state compared to that of the normal-state gap structures as manifested in ρ_c(T) transport and tunneling.     

Long-range alpha emission inP-wave neutron induced fission of235U

The yield and energy distribution of long-range alpha-particles (lra) emitted from neutron-induced fission of²³⁵U have been measured at neutron energies; thermal, 125±12, 155±11, 185±10, 210±9, 240±9, 365±50 and 480±45 keV. The long-range alpha-particles were detected in cellulose nitrate track detector foils. Results showed an increase of about 50% in the yield at neutron energies in the region 150 keV≤E _n≤220 keV as compared to that of thermal neutrons. A calculation has been carried out to extract thelra to binary fission ratio forp-wave neutron induced fission.     

Axiomatic Geometric Formulation of Electromagnetism with Only One Axiom: The Field Equation for the Bivector Field <Emphasis Type="Italic">F</Emphasis> with an Explanation of the Trouton-Noble Experiment

In this paper we present an axiomatic, geometric, formulation of electromagnetism with only one axiom: the field equation for the Faraday bivector field F. This formulation with F field is a self-contained, complete and consistent formulation that dispenses with either electric and magnetic fields or the electromagnetic potentials. All physical quantities are defined without reference frames, the absolute quantities, i.e., they are geometric four-dimensional (4D) quantities or, when some basis is introduced, every quantity is represented as a 4D coordinate-based geometric quantity comprising both components and a basis. The new observer-independent expressions for the stress-energy vector T(n) (1-vector), the energy density U (scalar), the Poynting vector S and the momentum density g (1-vectors), the angular momentum density M (bivector) and the Lorentz force K ((1-vector) are directly derived from the field equation for F. The local conservation laws are also directly derived from that field equation. The 1-vector Lagrangian with the F field as a 4D absolute quantity is presented; the interaction term is written in terms of F and not, as usual, in terms of A. It is shown that this geometric formulation is in a full agreement with the Trouton-Noble experiment.     

Spontaneous Symmetry Breaking in Presence of Electric and Magnetic Charges

Starting with the definition of quaternion gauge theory, we have undertaken the study of SU(2) _e ×SU(2) _m ×U(1) _e ×U(1) _m in terms of the simultaneous existence of electric and magnetic charges along with their Yang-Mills counterparts. As such, we have developed the gauge theory in terms of four coupling constants associated with four-gauge symmetry SU(2) _e ×SU(2) _m ×U(1) _e ×U(1) _m . Accordingly, we have made an attempt to obtain the abelian and non-Abelian gauge structures for the particles carrying simultaneously the electric and magnetic charges (namely dyons). Starting from the Lagrangian density of two SU(2)×U(1) gauge theories responsible for the existence of electric and magnetic charges, we have discussed the consistent theory of spontaneous symmetry breaking and Higgs mechanism in order to generate the masses. From the symmetry breaking, we have generated the two electromagnetic fields, the two massive vector W ^± and Z ⁰ bosons fields and the Higgs scalar fields.     

Distributions of transverse relaxation times for soft-solids measured in strongly inhomogeneous magnetic fields

The single-sided NMR-MOUSE sensor that operates in highly inhomogeneous magnetic fields is used to record a CPMG ¹H transverse relaxation decay by CPMG echo trains for a series of cross-linked natural rubber samples. Effective transverse relaxation rates 1/T_2,short and 1/T_2,long were determined by a bi-exponential fit. A linear dependence of transverse relaxation rates on cross-link density is observed for medium to large values of cross-link density. As an alternative to multi-exponential fits the possibility to analyze the dynamics of soft polymer network in terms of multi-exponential decays via the inverse Laplace transformation was studied. The transient regime and the effect of the T₁/T₂ ratio in inhomogeneous static and radiofrequency magnetic fields on the CPMG decays were studied numerically using a dedicated C++ program to simulate the temporal and spatial dependence of the CPMG response. A correction factor T₂/T_2,eff is derived as a function of the T₁/T₂ ratio from numerical simulations and compared with earlier results from two different well logging devices. High-resolution T₁–T₂ correlations maps are obtained by two-dimensional Laplace inversion of CPMG detected saturation recovery curves. The T₁–T₂ experimental correlations maps were corrected for the T₁/T₂ effect using the derived T₂/T_2,eff correction factor.     

Polarons in axial transport in single-layer high-T<Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> superconductors

The temperatureT dependencies ρ(T) of normal state electric resistivitiesρ _c (axial) andρ _ab (in plane) of single-layer high-T _c superconductors show common trends: AsT is raised, the resistivity first drops steeply before it starts rising αT above an apparent semiconductor-to-metal crossoverT _cross . To analyze ρ(T) we plottT/ρ againstT at various dopingsx for bothρ _c andρ _ab .T/ρ is inversely proportional to the traversal time across a potential barrier as an ionic particle drifts in an electric field. We findT/ρ in good agreement with theT dependence of the quantum rate of migrating particles: AsT is raised, a zero-point rate at the lowestT is extended to a nearly flat plateau before a thermally activated branch sets in. We also find evidence for the admixture of 1- & 2-phonon absorptions below the Arrhenius range. These features shape the semiconductor-like branch below T _cross . AboveT _cross a metallic-like branch sets in, its αT character deriving from the field coupling of the migrating particle. Our analysis suggests that metal physics may not suffice if ionic features play a role in transport. We attribute our conclusions to the drift of strong-coupling polarons along Cu−O bonds. These “bond polarons” originate from carrier scattering by double-well potentials associated with the bonds. A bond polaron dissociates to a free hole as it passes onto a neighboring O-O link.     

Effects of static magnetic fields on Escherichia coli

This paper represents the study of the biological effects of static magnetic fields (SMFs) on Escherichia coli (E. coli). The bacterial strain E. coli was exposed to SMFs in order to test its viability (evaluated by the number of colony-forming units (CFU)). In this study, we measured the dependence of CFU on the duration of exposure, on the treatment temperature T and on the value of the magnetic field induction B. The results showed that the number of CFU decreased with longer exposure time and higher treatment temperature (from 25 °C to 40 °C), whereas multiple extreme values of number of CFU were obtained when the induction B changed. In order to explain the results, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to investigate the morphology of the cells. We found obvious cell surface damage when the cells were exposed to SMFs.     

Magnetization of an electron plasma by microwave pulses: Faraday induction

It has been argued theoretically that the recently proposed vacuum fieldB ⁽³⁾ is not accompanied by a real electric fieldE ⁽³⁾ . Experimental evidence for this interence is available in the data reported by Deschampset al. [10], using microwave magnetization of an electron plasma set up in helium gas. Faraday induction due toB ⁽³⁾ does not occur in the inert gas and is not observed experimentally in the absence of free electrons. WheneverB ⁽³⁾ interacts with free electrons, however, Faraday induction occurs through a pulse of induced magnetization (i.e., induced orbital electronic angular momentum).     

Studies in nuclear macrophysics through fission and fission-like reactions

Recent developments in the study of fission and fission-like reactions are briefly reviewed. After a brief introduction of some of the important features of the fission process, binary fission and fission-like processes in heavy ion-induced reactions are discussed. It is shown that studies of the fission fragment angular distributions which provide a way to determine relative contributions of compound nucleus fission and non-equilibrium fission-like events in heavy ion-induced fission have proved to be quite valuable in investigating the very shortK-equilibration times of the order of 10⁻²⁰ s involved in the nuclear dynamics of the dinuclear complex on its way to compound nucleus formation following nucleus-nucleus collision.     

Indication for hyperdeformed cluster states in <Superscript>233</Superscript>Th

An activation technique was used to investigate relative yields of fission products from the reaction ²³²Th(n, f ) for neutron energies between 1.3 and 1.8MeV covering the region around the first hyperdeformed resonances. Intensities of characteristic γ-ray transitions were analyzed to search for changes in the mass distribution for neutron energies corresponding to the resonances and below the resonances. Relative increases in yield between 7 and 23% are observed for A ≈ 100 and 132 in the resonance region around 1.6MeV. It is proposed that the yield enhancement of daughter nuclei of the preformed fragments ¹³²Sn and ¹⁰¹Zr arises from cold fission of a di-cluster configuration. The experimental results support theoretical predictions for the existence of hyperdeformed octupole shapes based on the di-nuclear configuration ¹³²Sn + ¹⁰¹Zr.     

Two-Dimensional Quantum Hamiltonians with Shape Invariance Symmetry

It is shown that the Casimir operator associated with the U(1) Lie derivative defined on the S ²=SU(2)/U(1) base manifold, can be interpreted as Hamiltonians of a pair of scalar particle and scalar anti-particle with opposite charges over the S ² manifold in the presence of a magnetic monopole located at its origin and an external electric field. Using the SU(2) representation, the spectra of these Hamiltonians have been obtained. It is also proved that these Hamiltonians are isospectral and having the shape invariance symmetry, i.e. they are supersymmetric partner of each other. Also the Dirac’s quantization of magnetic charge comes very naturally from the finiteness of the SU(2) representation.     

密度泛函理论研究MgnOn(n=2—8)团簇的结构和电子性质

采用密度泛函理论中的广义梯度近似对Mg_nO_n(n=2—8)团簇的几何构型进行优化,并对能量、频率和电子性质进行了计算.结果表明,当n=2,3时,团簇的最低能量结构是平面结构;当n≥4时, 团簇的最低能量结构可以看成是由Mg₂O₂和Mg₃O₃单元组成的三维结构.O—Mg—O的钝角和较多的电荷转移对团簇的稳定性 关键词： nO_n团簇')" href="#">Mg_nO_n团簇 几何结构 电子性质