Particles in model filled rubber: Dispersion and mechanical properties

We have been able to design model filled rubbers with exactly the same chemical structure but different filler arrangements. From these model systems, we show that the particle arrangement in the elastomeric matrix controls the strain softening at small strain amplitude known as the Payne effect, as well as the elastic modulus dependence on the temperature. More precisely, we observed that the Payne effect disappears and the elastic modulus only weakly depends on the temperature when the particles are well separated. On the contrary, samples with the same interfacial physical chemistry but with aggregated particles show large amplitudes of the Payne effect and their elastic modulus decreases significantly with the temperature. We discuss these effects in terms of glassy bridge formation between filler particles. The observed effects provide evidence that glassy bridges play a key role on the mechanical properties of filled rubbers.     

External field-induced switching in nematic elastomers: A Monte Carlo study

We present a Monte Carlo study of external field-induced switching in nematic elastomers, employing a coarse-grained shearable lattice model. In large enough systems a full-wavelength Fréedericksz effect is observed --as opposed to the half-wavelength effect seen in ordinary nematics-- that clearly reflects in simulated polarized light textures, as well as in deuterium magnetic resonance spectra. The reorientation of mesogenic units is accompanied by pronounced shear deformations.     

Quantized dispersion of two-dimensional magnetoplasmons detected by photoconductivity spectroscopy

We find that the long-wavelength magnetoplasmon, resistively detected by photoconductivity spectroscopy in high-mobility two-dimensional electron systems, deviates from its well-known semiclassical nature as uncovered in conventional absorption experiments. A clear filling-factor dependent plateau-type dispersion is observed that reveals a so far unknown relation between the magnetoplasmon and the quantum Hall effect.     

Temperature Dependent In-Plane Anisotropic Magnetoresistance in HfTe_5 Thin Layers

We report the observation of in-plane anisotropic magnetoresistance and planar Hall effect in non-magnetic HfTe₅ thin layers.The observed anisotropic magnetoresistance as well as its sign is strongly dependent on the critical resistivity anomaly temperature T_p.Below T_p,the anisotropic magnetoresistance is negative with large negative magnetoresistance.When the in-plane magnetic field is perpendicular to the current,the negative longitudinal magnetoresistance reaches its maximum.The negative longitudinal magnetoresistance effect in HfTe₅ thin layers is dramatically different from that induced by the chiral anomaly as observed in Weyl and Dirac semimetals.One potential underlying origin may be attributed to the reduced spin scattering,which arises from the in-plane magnetic field driven coupling between the top and bottom surface states.Our findings provide valuable insights for the anisotropic magnetoresistance effect in topological electronic systems and the device potential of HfTe5 in spintronics and quantum sensing.     

Parametric excitation of a 1D gas in integrable and nonintegrable cases

We study the response of a highly excited 1D gas with pointlike interactions to a periodic modulation of the coupling constant. We calculate the corresponding dynamic structure factors and show that their low-frequency behavior differs dramatically for integrable and nonintegrable models. Nonintegrable systems are sensitive to excitations with frequencies as low as the mean level spacing, whereas much higher frequencies are required to excite an integrable system. This effect can be used as a probe of integrability for mesoscopic 1D systems and can be observed experimentally by measuring the heating rate of a parametrically excited gas.     

First-principles calculation of transport property in nano-devices under an external magnetic field

The mesoscopic quantum interference phenomenon （QIP） can be observed and behaves as the oscillation of conductance in nano-devices when the external magnetic field changes. Excluding the factor of impurities or defects, specific QIP is determined by the sample geometry. We have improved a first-principles method based on the matrix Green＇s function and the density functional theory to simulate the transport behaviour of such systems under a magnetic field. We have studied two kinds of QIP： universal conductance fluctuation （UCF） and Aharonov Bohm effect （A-B effect）. We find that the amplitude of UCF is much smaller than the previous theoretical prediction. We have discussed the origin of difference and concluded that due to the failure of ergodic hypothesis, the ensemble statistics is not applicable, and the conductance fluctuation is determined by the flux-dependent density of states （DOSs）. We have also studied the relation between the UCF and the structure of sample. For a specific structure, an atomic circle, the A-B effect is observed and the origin of the oscillation is also discussed.     

Quasiparticle dynamics in ferromagnetic compounds of the Co–Fe and Ni–Fe systems

We report a theoretical study of the quasiparticle lifetime and the quasiparticle mean free path caused by inelastic electron-electron scattering in ferromagnetic compounds of the Co–Fe and Ni–Fe systems. The study is based on spin-polarized calculations, which are performed within the G ⁰ W ⁰ approximation for equiatomic and Co(Ni)-rich compounds, as well as for their constituents. We mainly focus on the spin asymmetry of the quasiparticle properties, which leads to the spin-filtering effect experimentally observed in spin-dependent transport of hot electrons and holes in the systems under study. By comparing with available experimental data on the attenuation length, we estimate the contribution of the inelastic mean free path to this length.     

Kondo resonances and anomalous gate dependence in the electrical conductivity of single-molecule transistors

We report Kondo resonances in the conduction of single-molecule transistors based on transition metal coordination complexes. We find Kondo temperatures in excess of 50 K, comparable to those in purely metallic systems. The observed gate dependence of the Kondo temperature is inconsistent with observations in semiconductor quantum dots and a simple single-dot-level model. We discuss possible explanations of this effect, in light of electronic structure calculations.     

Coherent effects in crystal collimation

We present theory for coherent effects observed in crystal collimation experiments that is in good quantitative agreement with the RHIC and Tevatron data. We show that these effects are caused by a coherent scattering on the field of bent crystal atomic planes, which amplifies beam diffusion in accelerator by orders of magnitude compared to the scattering in amorphous material. This coherent scattering could replace the traditional amorphous scattering in accelerator collimation systems. We predict that for negative particles this effect is as strong as for positive ones, opening a principle way for efficient crystal steering of negative particles at accelerators. Predictions are made for high energy accelerators where crystal collimation is seen as an interesting application.     

Bifurcation and chaos in simple jerk dynamical systems

In recent years, it is observed that the third-order explicit autonomous differential equation, named as jerk equation, represents an interesting sub-class of dynamical systems that can exhibit many major features of the regular and chaotic motion. In this paper, we investigate the global dynamics of a special family of jerk systems {ie075-01}, whereG(x) is a non-linear function, which are known to exhibit chaotic behaviour at some parameter values. We particularly identify the regions of parameter space with different asymptotic dynamics using some analytical methods as well as extensive Lyapunov spectra calculation in complete parameter space. We also investigate the effect of weakening as well as strengthening of the non-linearity in theG(x) function on the global dynamics of these jerk dynamical systems. As a result, we reach to an important conclusion for these jerk dynamical systems that a certain amount of non-linearity is sufficient for exhibiting chaotic behaviour but increasing the non-linearity does not lead to larger regions of parameter space exhibiting chaos.     

Droplet state and the compressibility anomaly in dilute 2D electron systems

We investigate the space distribution of carrier density and the compressibility of two-dimensional (2D) electron systems by using the local density approximation. The strong correlation is simulated by the local exchange and correlation energies. A slowly varied disorder potential is applied to simulate the disorder effect. We show that the compressibility anomaly observed in 2D systems which accompanies the metal-insulator transition can be attributed to the formation of the droplet state due to a disorder effect at low carrier densities.     

Absolute negative conductivity and zero-resistance states in two-dimensional electron systems: A plausible scenario

We present a model that provides a plausible explanation of the effect of zero-resistance and zero-conductance states in two-dimensional electron systems subjected to a magnetic field and irradiated with microwaves observed in a number of experiments and of the effect’s main features. The model is based on the concept of absolute negative conductivity associated with photon-assisted scattering of electrons on impurities. It is shown that the main features of the effect can be attributed to the interplay of different electron scattering mechanisms.     

Screening model of magnetotransport hysteresis observed in bilayer quantum Hall systems

We report on theoretical and experimental investigations of a novel hysteresis effect that has been observed on the magnetoresistance of quantum Hall bilayer systems. Extending to these system a recent approach, based on the Thomas–Fermi–Poisson nonlinear screening theory and a local conductivity model, we are able to explain the hysteresis as being due to screening effects such as the formation of “incompressible strips”, which hinder the electron density in a layer within the quantum Hall regime to reach its equilibrium distribution.     

Heterogeneous dynamics of coarsening systems

We show by means of experiments, theory, and simulations that the slow dynamics of coarsening systems displays dynamic heterogeneity similar to that observed in glass-forming systems. We measure dynamic heterogeneity via novel multipoint functions which quantify the emergence of dynamic, as opposed to static, correlations of fluctuations. Experiments are performed on a coarsening foam using time-resolved correlation, a recently introduced light scattering method. Theoretically we study the Ising model, and present exact results in one dimension, and numerical results in two dimensions. For all systems the same dynamic scaling of fluctuations with domain size is observed.     

Hartman effect and nonlocality in quantum networks

We study the phase time for various quantum mechanical networks having potential barriers in their arms to find the generic presence of Hartman effect. In such systems it is possible to control the ‘super arrival’ time in one of the arms by changing parameters on another, spatially separated from it. This is yet another quantum nonlocal effect. Negative time delays (time advancement) and ‘ultra Hartman effect’ with negative saturation times have been observed in some parameter regimes.     

蒙特卡罗模拟在非平衡动态系统中的应用

非平衡系统几乎存在于自然和人造系统的各个层面上,它以非零连续的流量为特征。完全非对称简单排他过程被认为是对这类系统建模和模拟的一个范例。对蒙特卡罗方法如何模拟该类系统进行了介绍。分析了通过蒙特卡罗模拟观察到的一些有趣的物理现象如自发性对称破缺、有限尺寸效应和跳跃过程。非对称的低-低密度相破缺与系统的有限尺寸效应密切相关,建议开展更细致的蒙特卡罗模拟以进一步加深对仍处于争论中的非平衡系统有限尺寸效应的认识。     

Surface-level mechanistic studies of adsorbate-adsorbate interactions in heterogeneous catalysis by metals

Despite being considered a mature field, recent developments in experimental and theoretical techniques have greatly increased the fundamental understanding of complex surface processes in catalysis. One area of particular interest is the effect of co-adsorbed species on reactivity in heterogeneous systems. Experiments have demonstrated that co-adsorbed species, both organic and inorganic, can improve surface activity and selectivity. We begin by classifying adsorbate-adsorbate interactions that have been shown to alter the reactivity of a metal surface. We then review numerous systems where such effects have been observed using experiment or theory. Systems such as the hydrogenation of olefins with other carbonaceous adsorbates present, the chiral templating of surfaces, and the co-adsorption of alkalis, halides, and other inorganic “poisons” to improve selectivity are discussed in detail. Finally, future directions of study and outstanding questions are addressed.     

Doping dependent tunneling conductance in SDW ordered copper oxide superconductors

It is observed that doping suppresses the long range anti-ferromagnetic order and induces superconducting phase for a suitable doping. In order to study this effect, we present a model study of the doping dependence of the tunneling conductance in high-T_c systems. The system is described by the Hamiltonian consisting of spin density wave (SDW) and s-wave type superconducting interaction in presence of varying impurity concentrations. The gap equations are calculated by using Green’s functions technique of Zubarev. The gap equations and the chemical potential are solved self-consistently. The imaginary part of the electron Green’s functions shows the quasi-particle density of states which represent the tunneling conductance observed by the scanning tunneling microscopy (STM). We investigate the effect of impurity on the gap equations as well as on the tunneling conductance. The results will be discussed based on the experimental observations.     

Detecting the Kondo screening cloud around a quantum dot

A fundamental prediction of scaling theories of the Kondo effect is the screening of an impurity spin by a cloud of electrons spread out over a mesoscopic distance. This cloud has never been observed experimentally. Recently, aspects of the Kondo effect have been observed in experiments on quantum dots embedded in quantum wires. Since the length of the wire may be of order the size of the screening cloud, such systems provide an ideal opportunity to observe it. We point out that persistent current measurements in a closed ring provide a conceptually simple way of detecting this fundamental length scale.