查看更多>>摘要：The two-dimensional(2D)Janus monolayers are promising in spintronic device application due to their enhanced magnetic couplings and Curie temperatures.Van der Waals CrCl3 monolayer has been experimentally proved to have an in-plane magnetic easy axis and a low Curie temperature of 17 K,which will limit its application in spintronic devices.In this work,we propose a new Janus monolayer Cr2Cl3S3 based on the first principles calculations.The phonon dispersion and elastic constants confirm that Janus monolayer Cr2Cl3S3 is dynamically and mechanically stable.Our Monte Carlo simulation results based on magnetic exchange constants reveal that Janus monolayer Cr2Cl3S3 is an intrinsic ferromagnetic semiconductor with TC of 180 K,which is much higher than that of CrCl3 due to the enhanced ferromagnetic coupling caused by S substitution.Moreover,the magnetic easy axis of Janus Cr2Cl3S3 can be tuned to the perpendicular direction with a large magnetic anisotropy energy(MAE)of 142 peV/Cr.Furthermore,the effect of biaxial strain on the magnetic property of Janus monolayer Cr2Cl3S3 is evaluated.It is found that the Curie temperature is more robust under tensile strain.This work indicates that the Janus monolayer Cr2Cl3S3 presents increased Curie temperature and out-of-plane magnetic easy axis,suggesting greater application potential in 2D spintronic devices.
查看更多>>摘要：Exploring novel two-dimensional(2D)valleytronic materials has an essential impact on the design of spintronic and valleytronic devices.Our first principles calculation results reveal that the Janus SWSiX2(X=N,P,As)monolayer has excellent dynamical and thermal stability.Owing to strong spin-orbit coupling(SOC),the SWSiX2 monolayer exhibits a valence band spin splitting of up to 0.49 eV,making it promising 2D semiconductor for valleytronic applications.The opposite Berry curvatures and optical selection rules lead to the coexistence of valley and spin Hall effects in the SWSiX2 monolayer.Moreover,the optical transition energies can be remarkably modulated by the in-plane strains.Large tensile(compressive)in-plane strains can achieve spin flipping in the SWSiN2 monolayer,and induce both SWSiP2 and SWSiAs2 monolayers transit from semiconductor to metal.Our research provides new 2D semiconductor candidates for designing high-performance valleytronic devices.
查看更多>>摘要：The heat transfer and stability of methane hydrate in reservoirs have a direct impact on the drilling and production efficiency of hydrate resources,especially in complex stress environments caused by formation subsidence.In this study,we investigated the thermal transport and structural stability of methane hydrate under triaxial compression using molecular dynamics simulations.The results suggest that the thermal conductivity of methane hydrate increases with increasing compression strain.Two phonon transport mechanisms were identified as factors enhancing thermal conductivity.At low compressive strains,a low-frequency phonon transport channel was established due to the overlap of phonon vibration peaks between methane and water molecules.At high compressive strains,the filling of larger phonon bandgaps facilitated the opening of more phonon transport channels.Additionally,we found that a strain of-0.04 is a watershed point,where methane hydrate transitions from stable to unstable.Furthermore,a strain of-0.06 marks the threshold at which the diffusion capacities of methane and water molecules are at their peaks.At a higher strain of-0.08,the increased volume compression reduces the available space,limiting the diffusion ability of water and methane molecules within the hydrate.The synergistic effect of the strong diffusion ability and high probability of collision between atoms increases the thermal conductivity of hydrates during the unstable period compared to the stable period.Our findings offer valuable theoretical insights into the thermal conductivity and stability of methane hydrates in reservoir stress environments.
查看更多>>摘要：The AFM probe in tapping mode is a continuous process of energy dissipation,from moving away from to intermittent contact with the sample surfaces.At present,studies regarding the energy dissipation mechanism of this continuous process have only been reported sporadically,and there are no systematic explanations or experimental verifications of the energy dissipation mechanism in each stage of the continuous process.The quality factors can be used to characterize the energy dissipation in TM-AFM systems.In this study,the vibration model of the microcantilever beam was established,coupling the vibration and damping effects of the microcantilever beam.The quality factor of the vibrating microcantilever beam under damping was derived,and the air viscous damping when the probe is away from the sample and the air squeeze film damping when the probe is close to the sample were calculated.In addition,the mechanism of the damping effects of different shapes of probes at different tip-sample distances was analyzed.The accuracy of the theoretical simplified model was verified using both experimental and simulation methods.A clearer understanding of the kinetic characteristics and damping mechanism of the TM-AFM was achieved by examining the air damping dissipation mechanism of AFM probes in the tapping mode,which was very important for improving both the quality factor and the imaging quality of the TM-AFM system.This study's research findings also provided theoretical references and experimental methods for the future study of the energy dissipation mechanism of micro-nano-electromechanical systems.
查看更多>>摘要：We have applied strong coupling unitary transformation method combined with Bose-Einstein statistical law to inves-tigate magnetopolaron energy level temperature effects in halogen ion crystal quantum wells.The obtained results showed that under magnetic field effect,magnetopolaron quasiparticle was formed through the interaction of electrons and sur-rounding phonons.At the same time,magnetopolaron was influenced by phonon temperature statistical law and important energy level shifts down and binding energy increases.This revealed that lattice temperature and magnetic field could easily affect magnetopolaron and the above results could play key roles in exploring thermoelectric conversion and conductivity of crystal materials.
查看更多>>摘要：The realization of 100％polarized topological Weyl fermions in half-metallic ferromagnets is of particular importance for fundamental research and spintronic applications.Here,we theoretically investigate the electronic and topological prop-erties of the zinc-blende compound VAs,which was deemed as a half-metallic ferromagnet related to dynamic correlations.Based on the combination of density functional theory and dynamical mean field theory,we uncover that the half-metallic ferromagnet VAs exhibits attractive Weyl semimetallic behaviors which are very close to the Fermi level in the DFT+U regime with effect U values ranging from 1.5 eV to 2.5 eV.Meanwhile,we also investigate the magnetization-dependent topological properties;the results show that the change of magnetization directions only slightly affects the positions of Weyl points,which is attributed to the weak spin-orbital coupling effects.The topological surface states of VAs projected on semi-infinite(001)and(111)surfaces are investigated.The Fermi arcs of all Weyl points are clearly visible on the pro-jected Fermi surfaces.Our findings suggest that VAs is a fully spin-polarized Weyl semimetal with many-body correlated effects in the effective U values range from 1.5 eV to 2.5 eV.
查看更多>>摘要：Heterostructures of van der Waals(vdW)ferromagnetic materials have become a focal point in research of low-dimensional spintronic devices.The current direction in spin valves is commonly perpendicular to the plane(CPP).How-ever,the transport properties of the CPP mode remain largely unexplored.In this work,current-in-plane(CIP)mode and CPP mode for CrTe2 thin films are carefully studied.The temperature-dependent longitudinal resistance transitions from metallic(CIP)to semiconductor behavior(CPP),with the electrical resistivity of CPP increased by five orders of magni-tude.More importantly,the transport properties of the CPP can be categorized into a single-gap tunneling-through model with the activation energy(Ea)of～1.34 meV/gap at 300-150 K,the variable range hopping model with a linear negative magnetoresistance at 150-20 K,and weak localization region with a nonlinear magnetic resistance below 20 K.This study explores the vertical transport in CrTe2 materials for the first time,contributing to understand its unique properties and to pave the way for its potential in spin valve devices.
查看更多>>摘要：The spin pumping effect in magnetic heterostructures and multilayers is a highly effective method for the generation and transmission of spin currents.In the increasingly prominent synthetic antiferromagnetic structures,the two ferromag-netic layers demonstrate in-phase and out-of-phase states,corresponding to acoustic and optical precession modes.Within this context,our study explores the spin pumping effect in Py/Ru/Py synthetic antiferromagnetic structures across different modes.The heightened magnetic damping resulting from the spin pumping effect in the in-phase state initially decreases with increasing Py thickness before stabilizing.Conversely,in the out-of-phase state,the amplified damping exceeds that of the in-phase state,suggesting a greater spin relaxation within this configuration,which demonstrates sensitivity to alter-ations in static exchange interactions.These findings contribute to advancing the application of synthetic antiferromagnetic structures in magnonic devices.
查看更多>>摘要：We develop a numerical method for the time evolution of Gaussian wave packets on flat-band lattices in the presence of correlated disorder.To achieve this,we introduce a method to generate random on-site energies with prescribed correlations.We verify this method with a one-dimensional(1D)cross-stitch model,and find good agreement with analytical results obtained from the disorder-dressed evolution equations.This allows us to reproduce previous findings,that disorder can mobilize 1D flat-band states which would otherwise remain localized.As explained by the corresponding disorder-dressed evolution equations,such mobilization requires an asymmetric disorder-induced coupling to dispersive bands,a condition that is generically not fulfilled when the flat-band is resonant with the dispersive bands at a Dirac point-like crossing.We exemplify this with the 1D Lieb lattice.While analytical expressions are not available for the two-dimensional(2D)system due to its complexity,we extend the numerical method to the 2D α-T3 model,and find that the initial flat-band wave packet preserves its localization when α=0,regardless of disorder and intersections.However,when α≠0,the wave packet shifts in real space.We interpret this as a Berry phase controlled,disorder-induced wave-packet mobilization.In addition,we present density functional theory calculations of candidate materials,specifically Hg1-xCdxTe.The flat-band emerges near the Г point(k=0)in the Brillouin zone.
查看更多>>摘要：Quantum confinement is recognized to be an inherent property in low-dimensional structures.Traditionally,it is believed that the carriers trapped within the well cannot escape due to the discrete energy levels.However,our previous research has revealed efficient carrier escape in low-dimensional structures,contradicting this conventional understanding.In this study,we review the energy band structure of quantum wells along the growth direction considering it as a super-position of the bulk material dispersion and quantization energy dispersion resulting from the quantum confinement across the whole Brillouin zone.By accounting for all wave vectors,we obtain a certain distribution of carrier energy at each quantized energy level,giving rise to the energy subbands.These results enable carriers to escape from the well under the influence of an electric field.Additionally,we have compiled a comprehensive summary of various energy band scenarios in quantum well structures relevant to carrier transport.Such a new interpretation holds significant value in deepening our comprehension of low-dimensional energy bands,discovering new physical phenomena,and designing novel devices with superior performance.
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