Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The flexoelectric effect, referred as the strain gradient induced polarization, widely exists in dielectric materials, but few research groups so far have reported its molecular dynamics studies. In this study, the radial distribution function of BaTiO<jats:sub>3</jats:sub> and the phase transition temperatures have been researched, which showed that the core-shell potential model is effective and the structure of BaTiO<jats:sub>3</jats:sub> is stable in 10-150 K. Simulated hysteresis loops of BaTiO<jats:sub>3</jats:sub> by molecular dynamics show that anisotropy can play an important role in the coercive field. Based on the rational simulation process, the cantilever beam bent angle and fixed length effects on the polarization were focused and analyzed. It was found that the small bent angle of the curved cantilever beam can give a proportional relationship with a fixed end length and a non-linear relationship is present when the bent angle is much larger. The prediction of flexoelectric coefficient in BaTiO<jats:sub>3</jats:sub> is 18.5 nC/m. This work provides a computational framework for the study of flexoelectric effect using molecular dynamics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the spatial structure and sympathetic cooling of the bi-component Coulomb crystal (CC) which consists of approximate 450 <jats:sup>9</jats:sup>Be<jats:sup>+</jats:sup> ions and 450 <jats:sup>40</jats:sup>Ca<jats:sup>+</jats:sup> ions with a mass ratio of 0.225 in a segmented linear ion trap. By two-dimensional imaging of the bi-component CC, the <jats:sup>9</jats:sup>Be<jats:sup>+</jats:sup> ions are found to be surrounded by the <jats:sup>40</jats:sup>Ca<jats:sup>+</jats:sup> ions in the radial direction with a separation ratio of ~2.0, and the axial length of the <jats:sup>9</jats:sup>Be<jats:sup>+</jats:sup> ions occupied area is much larger than that of the <jats:sup>40</jats:sup>Ca<jats:sup>+</jats:sup> ions occupied area. Combined with the previous experimental results, the structure of the <jats:sup>9</jats:sup>Be<jats:sup>+</jats:sup>-<jats:sup>40</jats:sup>Ca<jats:sup>+</jats:sup> CC shows the larger the difference in the mass-charge ratio, the larger the separation between the two species. The comparison of the fluorescence spectra of the <jats:sup>9</jats:sup>Be<jats:sup>+</jats:sup> ions in the bi-component CC and the pure CC indicates that the <jats:sup>9</jats:sup>Be<jats:sup>+</jats:sup> ions can be sympathetically cooled and stably localized by the laser-cooled <jats:sup>40</jats:sup>Ca<jats:sup>+</jats:sup> ions during the recording of the fluorescence spectrum.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The influence of the vacuum polarization effects in the interactions of multiple ultra-intense lasers with plasmas are discussed. The nonlinear paraxial monochromatic model of the interactions has been improved by considering the Heisenberg-Euler Lagrangian density of two laser processes. Comparing the corrections of the vacuum polarization effects in collision of laser beams with the one generated by a single intense laser, we find that the former has a higher order of magnitude correction. The laser collision also produces varies in the propagation direction and polarization direction of the lasers propagating in the plasma. In addition, the strong-field quantum electrodynamics (QED) effects can be enhanced by increasing the laser intensity, frequency difference or adjusting the incident angle of the two laser beams.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The applications of metasurfaces are currently a highly active field of research due to their extraordinary capacity to manipulate electromagnetic waves. The ultra-thin characteristics of metasurfaces allow the miniaturization and integration of metasurface devices. However, these devices typically suffer from a low efficiency and narrow bandwidth conditions. In this paper, we design eight multilayered unit cells with similar amplitudes and a phase with an interval of π/4, which convert the polarization states of the terahertz (THz) waves between two orthogonal directions. The average cross-polarized transmission amplitude of these cells is around 0.9 within the ultra-broad frequency regions ranging from 0.5 to 1.4 THz. Furthermore, unit cells are used to construct both an ultra-thin anomalous refraction metalens and a vortex phase plate. Our simulation results show that the anomalous refraction for the transmitted linear polarization component is comparable to the theoretical predictions, and the maximum error is determined to be below 4.8%. The vortex phase plate can also generate an ideal terahertz vortex beam with a mode purity of 90% and above. The distributions of longitudinal electric field, intensity and phase illustrate that the generated vortex beam has excellent propagation characteristics and a weak divergence. Simulations of the two types of metasurface devices, based on the eight unit cells, exhibit very high efficiencies in a wide bandwidth. Our research will assist in the improvement for the practical applications of metasurfaces. It also provides a reference for the design of high efficiency and broadband devices that apply to other frequency ranges.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the Kondo screening of a spin-1/2 magnetic impurity coupled to a superconductor, which is fabricated by the combination of an <jats:italic>s</jats:italic>-wave superconductor, a ferromagnet and a semiconductor with Rashba spin-orbit coupling (RSOC). The proximity induced superconducting states include the <jats:italic>s</jats:italic>-wave and <jats:italic>p</jats:italic>-wave pairing components with the aids of RSOC, and the ferromagnet induces a Zeeman field which removes the spin degeneracy of the quasiparticles in the triplet states. Thus, the Kondo screening of magnetic impurity involves the orbital degrees of freedom, and is also affected by the Zeeman field. By using the variational method, we calculate the binding energy and the spin-spin correlation between the magnetic impurity and the electrons in the co-existing <jats:italic>s</jats:italic>-wave and <jats:italic>p</jats:italic>-wave pairing states. We find that Kondo singlet forms more easily with stronger RSOC, but Zeeman field in general decreases the binding energy. The spin-spin correlation decays fast in the vicinity of the magnetic impurity. Due to the RSOC, the spatial spin-spin correlation becomes highly anisotropic, and the Zeeman field can induce extra asymmetry to the off-diagonal components of the spin-spin correlation. Our study can offer some insights into the studies of extrinsic topological superconductors fabricated from the hybrid structures containing chains of magnetic impurities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Yb<jats:sup>3+</jats:sup>:CaF<jats:sub>2</jats:sub>-YF<jats:sub>3</jats:sub> transparent ceramics with excellent optical quality was successfully fabricated by hot-pressed method. Pulsed laser properties of this ceramics were investigated for the first time. Laser diode (LD) was applied as the pump source to generate a dual-wavelength mode-locked (ML) laser. The maximum average output power was 310 mW, represents the highest output power of ultrafast calcium fluoride ceramic laser. The spectrum separated at 1048.9 nm and 1049.7 nm with a total pulse duration of 8.9 ps. The interval period between the beating signals was about 4.3 ps, corresponding to a 0.23 THz beat pulse repetition rate. These results demonstrate its potential in producing dual-wavelength ultrashort pulses, enabling these Yb<jats:sup>3+</jats:sup>:CaF<jats:sub>2</jats:sub>-YF<jats:sub>3</jats:sub> ceramics with low-cost and short-preparation period are ideal candidates material for ultrafast lasers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The preparation and control of cold molecules are advancing rapidly, motivated by many exciting applications, ranging from tests of fundamental physics to quantum information processing. Here, we proposed a trapping scheme to create high-density cold molecular samples using a combination of electric and magnetic fields. In our theoretical analysis and numerical calculations, a typical alkaline-earth monofluoride, MgF, is used to test the feasibility of our proposal. A cold MgF molecular beam is firstly produced via an electrostatic Stark decelerator and then loaded into the proposed electromagnetic trap, which is composed of an anti-Helmholtz coil, an octupole, and two disk electrodes. Following that, a huge magnetic force is applied to the molecular sample at an appropriate time, which enables further compressing of the spatial distribution of the cold sample. Molecular samples with both higher number density and smaller volume are quite suitable for the next step of laser confinement and other molecular experiments such as cold collisions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>With an external in-plane magnetic field, we show the emergence of a topological nodal superconducting phase of the two-dimensional topological surface states. This nodal superconducting phase is protected by the chiral symmetry with non-zero magnetic field, and there are corresponding Majorana Fermi arcs (also known as flat band Andreev bound states) connecting the two Majorana nodes along the edges similar to the case of Weyl semimetal. The topological nodal superconductor is an intermediate phase between two different chiral superconductors, and is stable against the effects of substrates. The two-dimensional effective theory of the nodal superconducting phase also captures the low energy behavior of a three-dimensional lattice model which describes the iron-based superconductor with a thin film geometry. The localizations of the Majorana nodes can be manipulated through external in-plane magnetic fields, which may introduce a non-trivial topological Berry phase between them.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The variational principle of minimum free energy (MFEVP) has been widely used in the study of soft matter statics. MFEVP can be used not only to derive equilibrium equations (including both bulk equations and boundary conditions), but also to develop direct variational methods (such as Ritz method) to find approximate solutions to these equilibrium equations. In this work, we applied these variational methods to study long-range force transmission in nonlinear elastic biopolymer gels. We showed that the slow decay of cell-induced displacements measured experimentally for fibroblast spheroids in three-dimensional fibrin gels can be well explained by variational approximations based on the three-chain model of biopolymer gels.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A scheme is proposed to investigate the non-classical states generated by quantum scissors device (QSD) operating on the the cavity mode of optomechanical system. When the catalytic QSD acting on the cavity mode of optomechanical system, the resulting state contains only the vacuum, single-photon and two-photon states depending upon the coupling parameter of optomechanical system as well as the transmission coefficients of beam splitters. Especially, the output state is just a class of multicomponent cat state truncations at time <jats:italic>t</jats:italic> = 2<jats:italic>π</jats:italic> by choosing the appropriate value of coupling parameter. We have discussed the success probability of such state and the fidelity between the output state and input state via QSD. Then the linear entropy is used to investigate the entanglement between the two subsystems, which finds that QSD operation can enhance their entanglement degree. Further-more, we also derive the analytical expression of Wigner function (WF) for the cavity mode via QSD and numerically discuss the WF distribution in phase space at time <jats:italic>t</jats:italic> = 2<jats:italic>π</jats:italic>. These results show that the high non-classicality of output state can always be achieved by modulating the coupling parameter of optomechanical system as well as the transmittance of beam splitters.</jats:p>