Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Superconducting wire-networks are paradigms to study Cooper pairing issues, vortex dynamics and arrangements. Recently, emergent low-dimensional crystalline superconductors are reported in the minimal-disorder limit, providing novel platforms to reveal vortices-related physics. Study on superconducting loops with high-crystallinity is thus currently demanded. Here, we report fabrication and transport measurement of finite square-network based on two-dimensional crystalline superconductor Mo<jats:sub>2</jats:sub>C. We observe oscillations in the resistance as a function of the magnetic flux through the loops. Resistance dips at both matching field and fractional fillings are revealed. Temperature and current evolutions are carried out in magnetoresistance to study vortex dynamics. The amplitude of oscillation is enhanced due to the interaction between thermally activated vortices and the currents induced in the loops. The driving current reduces effective activation energy for vortex, giving rise to stronger vortex interaction. Moreover, by thermally activated vortex creep model, we derive effective potential barrier for vortex dissipation, which shows well-defined correspondence with structures in magnetoresistance. Our work shows that low-dimensional crystalline superconducting network based on Mo<jats:sub>2</jats:sub>C possesses pronounced potential in studying the modulation of vortex arrangements and dynamics, paving the way for further investigations on crystalline superconducting network with various configurations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The influence of undercooling and cooling rate on the microstructural evolution of ternary Cu<jats:sub>45</jats:sub>Zr<jats:sub>45</jats:sub>Ag<jats:sub>10</jats:sub> alloy using single-roller melt spinning and drop tube was investigated. The rapidly quenched alloy ribbons achieve a homogeneous glass structure. The microstructure of the droplets transformed from the Cu<jats:sub>10</jats:sub>Zr<jats:sub>7</jats:sub> dendrites plus (Cu<jats:sub>10</jats:sub>Zr<jats:sub>7</jats:sub>+AgZr) eutectic to Cu<jats:sub>10</jats:sub>Zr<jats:sub>7</jats:sub> dendrites with the decrease of droplet diameter. As the diameter decreases to 180 μm, the Cu<jats:sub>45</jats:sub>Zr<jats:sub>45</jats:sub>Ag<jats:sub>10</jats:sub> alloy changes from crystal to amorphous structure. It shows that the cooling rate is not the only influence factor and the undercooling play a certain role in the formation of the amorphous alloy at the same time under microgravity condition.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Y<jats:sub>3</jats:sub>Fe<jats:sub>5</jats:sub>O<jats:sub>12</jats:sub> (YIG) and BiY<jats:sub>2</jats:sub>Fe<jats:sub>5</jats:sub>O<jats:sub>12</jats:sub> (Bi:YIG) films are epitaxially grown on a series of (111)-oriented garnets substrates using pulsed laser deposition. Structural and ferromagnetic resonance characterizations demonstrate the high epitaxial quality, extremely low magnetic loss, and coherent strain state in these films. Using these epitaxial films as model systems, we systematically investigate the evolutions of magnetic anisotropy (MA) with epitaxial strain and chemical doping. For both the YIG and Bi:YIG films, the compressive strain tend to align the magnetic moment in film plane, while the tensile strain can compete with the demagnetization effect and stabilize a perpendicular MA. We found that the strain induced lattice elongation/compression along the out-of-plane[111] axis is the key parameter that determines the MA. More importantly, the strain-induced tunability of MA can be enhanced significantly by Bi doping, and meanwhile, the ultra-low damping feature persists. We clarified that the cooperation between strain and chemical doping could realize an effective control of MA in garnet-type ferrites, which is essential for spintronic applications.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Based on first-principles calculations, a two-dimensional (2D) van der Waals (vdW) bilayer heterostructure consisting of two topologically trivial ferromagnetic (FM) monolayers CrI<jats:sub>3</jats:sub> and ScCl<jats:sub>2</jats:sub> is proposed to realize the quantum anomalous Hall effect (QAHE) with a sizable topologically nontrivial band gap of 4.5 meV. Its topological nature is attributed to an interlayer band inversion between the monolayers and critically depends on the symmetry of the stacking configuration. We further demonstrate that the topologically nontrivial band gap can be increased nearly linearly by the application of a perpendicular external pressure and reaches 8.1 meV at 2.7 GPa, and the application of an external out-of-plane electric field can also modulate the band gap and convert the system back to topologically trivial via eliminating the band inversion. An effective model is developed to describe the topological phase evolution in this bilayer heterostructure. This work provides a new candidate system based on 2D vdW materials for the realization of potential high-temperature QAHE with considerable controllability.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Based on the coherent interaction and action-counteraction principles,we investigate for small polaron systems the ground state properties, the coherent-squeezed fluctuation correction,and the anomalous lattice quantum fluctuation, with the new variational generator containing correlated squeezed-coherent coupling and quantum entanglement.Noting that -2<jats:italic>t</jats:italic> is the T.B.A. energy, for coherent interaction effect, we find the ground-state energy <jats:italic>E</jats:italic>。to be -2.428<jats:italic>t</jats:italic>, in which the coherent squeezed fluctuation correction -<jats:italic>A</jats:italic>。<jats:italic>t</jats:italic> is -0.463<jats:italic>t</jats:italic>(where <jats:italic>t</jats:italic> is the hopping integral, <jats:italic>ω</jats:italic> is the phonon frequency),with the electron-one-phonon coupling constant <jats:italic>g</jats:italic>=1 and the electron-two-phonon coupling constant <jats:italic>g</jats:italic> <jats:sub>1</jats:sub>=-0.1. However, as the result of the action-counteraction effect, $\mathop E\limits^ \sim $<jats:sub>0</jats:sub> is -2.788<jats:italic>t</jats:italic>,but -$\mathop A\limits^ \sim $<jats:sub>0</jats:sub> <jats:italic>t</jats:italic> is -0.735<jats:italic>t</jats:italic>.As to the polaron binding energy(<jats:italic>E</jats:italic> <jats:sub> <jats:italic>P</jats:italic> </jats:sub>), for the coherent interaction effect, <jats:italic>E</jats:italic> <jats:sub> <jats:italic>P</jats:italic> </jats:sub> is -1.38<jats:italic>ω</jats:italic>, but for the action-counteraction effect, <jats:italic>E</jats:italic> <jats:sub> <jats:italic>P</jats:italic> </jats:sub> is -1.88<jats:italic>ω</jats:italic>. In particular the electron-two-phonon interaction noticeably enlarge the coherent interaction and the coherent squeezed quantum fluctuation correction. By intervening the quantum entanglement, the evolutions of the squeezed coherent state and the lattice quantum fluctuation become to control. At that time we encounter a new quantum phase coherence phenomena,the collapse and revival of inversion repeatedly for the coherent state in the entangled evolution.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this work, we investigate the quantum entanglement in a non-Hermitian kicking system. In Hermitian case, the out-of-time ordered correlators (OTOCs) exhibit the unbounded power-law increase with time. Correspondingly, the linear entropy, which is a common measurement of entanglement, rapidly increases from zero to almost unity, indicating the formation of quantum entanglement. For strong enough non-Hermitian driving, both the OTOCs and linear entropy rapidly saturate as time evolves. Interestingly, with the increase of non-Hermitian kicking strength, the long-time averaged value of both OTOCs and linear entropy has the same transition point where they exhibit the sharp decrease from a plateau, demonstrating the disentanglment. We reveal the mechanism of disentanglement with the extension of Floquet theory to non-Hermitian system.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The lower hybrid current drive is a potential candidate for sustaining plasma current in tokamak steady state operations, which could be used in China Fusion Engineering Test Reactor (CFETR) with input power up to a few ten megawatts. Such high input power could trigger the well-known parametric instabilities (PIs) at the plasma edge affecting the propagation and absorption of the lower hybrid pump waves, which is studied in this paper. By analyzing the expression of PI growth rates solved from the nonlinear dispersion relation, it is found that the pressure is the key parameter determining the PI characteristics. Ion sound quasi-mode (ISQM) is the dominant decay channel in the low pressure regime, while the ion cyclotron quasi-mode (ICQM), as well as its harmonics, becomes dominant in the intermediate regime. In the high pressure regime, only one mixed channel is found, which is related to Landau damping by free-streaming ions. Analytical expressions of growth rates of these decay channels are also obtained to show the parameter dependences at different pressure limits. The above analytical results are used to estimate the PIs on a typical profile of CFETR, and verified by corresponding numerical calculations. ICQM is found to be the strongest decay channel with a considerable growth rate for CFETR.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a cascaded nonlinear spectral broadening scheme for Nd-doped lasers, featuring with long pulse duration and high average power. This scheme is based on two multi-pass cells (MPCs) and one multiple-plate supercontinuum generation (MPSG), and the numerical investigation is driven by a home-made Nd-doped fiber laser with 12 ps pulse duration, 50 kHz repetition rate and 100 W average power. The MPC based first two stages allowing us to broaden the pulse spectrum to 4 nm and 43 nm respectively and, subsequently, the MPSG based third stage allowing us to reach 235 nm spectral bandwidth. This broadened spectrum can support a Fourier-transfer-limited (FTL) pulse duration of 9.8 fs, which is shorter than three optical cycles. To the best of our knowledge, it is the first time to demonstrate the possibility of few-cycle pulses generation based on the 10 ps level Nd-doped lasers. Such few-cycle and high average power laser sources should be attractive and prospective, benefiting from the characteristics of structure compact, low-cost and flexibility.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Laser-induced breakdown spectroscopy (LIBS) is a good technique for detecting and analyzing material elements due the plasma emission produced by a high-power laser pulse. At present, an important topic of LIBS research is to improve the emission intensity of LIBS. This study investigated the effect of laser-polarization on femtosecond laser-ablated Cu plasma spectra at different sample temperatures. The measured lines under circularly polarized laser was higher than those under linearly and elliptically polarized lasers. And the enhancement effect was more evident at higher Cu temperatures by comparing the plasma spectra with circular and linear polarizations for different target temperatures. To understand the influences of laser-polarization and sample temperature on the signal intensity, the plasma temperature (PT) and electron density (ED) were calculated. The change in the PT and ED was consistent with the change in the atomic lines as adjusting the laser polarization. With raising the Cu temperature, the PT increased while the ED decreased. The combination of raising the Cu temperature and adjusting the laser-polarization is much more effective for improving the signal of femtosecond LIBS compared to raising the initial sample temperature alone or changing only the laser-polarization.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>GeSe has recently emerged as a photovoltaic absorber material due to its attractive optical and electrical properties as well as earth abundancy and low toxicity. However, the efficiency of GeSe thin-film solar cells (TFSCs) is still low compared to the Shockley-Queisser limit. Point defects are believed to play important roles in the electrical and optical properties of GeSe thin films. Here, we perform first-principles calculations to study the defect characteristics of GeSe. Our results demonstrate that no matter under the Ge-rich or Se-rich condition, the Fermi level is always located near the valence band edge, leading to the <jats:italic>p</jats:italic>-type conductivity of undoped samples. Under Se-rich condition, the Ge vacancy (V<jats:sub>Ge</jats:sub>) has the lowest formation energy, with a (0/2–) charge-state transition level at 0.22 eV above the valence band edge. The high density (above 10<jats:sup>17</jats:sup> cm<jats:sup>-3</jats:sup>) and shallow level of V<jats:sub>Ge</jats:sub> imply that it is the <jats:italic>p</jats:italic>-type origin of GeSe. Under Se-rich growth condition, Se<jats:sub>i</jats:sub> has a low formation energy in the neutral state, but it does not introduce any defect level in the band gap, suggesting that it neither contributes to electrical conductivity nor induces non-radiative recombination. In addition, Ge<jats:sub>i</jats:sub> introduces a deep charge-state transition level, making it a possible recombination center. Therefore, we propose that the Se-rich condition should be adopted to fabricate high-efficiency GeSe solar cells.</jats:p>