Table of contents

We study strong interaction effects in a one-dimensional (1D) boson gas across a narrow confinement-induced resonance (CIR). In contrast to the zero-range potential, the 1D two-body interaction in the narrow CIR can be written as a polynomial of derivative δ-function interaction on many-body level. Using the asymptotic Bethe ansatz, we find that the low-energy physics of this many-body problem is described by the Tomonaga-Luttinger liquid where the Luttinger parameters are essentially modified by an effective finite-range parameter v. This parameter drastically alters quantum criticality and universal thermodynamics of the gas. In particular, it drives the Tonks-Girardeau (TG) gas from non-mutual Fermi statistics to mutual statistics or to a more exclusive super-TG gas. This novel feature is further discussed in terms of the breathing mode which is experimentally measurable.

In this paper we study strange matter by investigating the stability window within one version of the QMDD model which suffers a thermodynamic inconsistency at zero temperature and check that it can explain the very massive pulsar recently detected. We compare our results with the ones obtained within the MIT bag model and see that this version of the QMDD model can explain larger masses, due to the stiffening of the equation of state.

Conical intersections between molecular electronic potential energy surfaces can greatly affect molecular dynamics and chemical properties. Molecular gauge theory is capable of explaining many of these often unexpected phenomena deriving from the physics of the conical intersection. Here we will give an example of anomalous dynamics in the paradigm E ×  Jahn-Teller model, which does not allow for a simple explanation in terms of standard molecular gauge theory. By introducing a dual gauge theory, we unwind this surprising behavior by identifying it with an intrinsic spin Hall effect. Thus, this work link knowledge of condensed-matter theories with non-adiabatic molecular dynamics. Furthermore, via ab initio calculations of potential energy surfaces, the findings are as well demonstrated to appear in a realistic system such as the Li₃ molecule.

We present the theory for a retarded resonance interaction between two identical atoms near a dielectric surface. In free space the resonance interaction between isotropically excited atom pairs is attractive at all atom-atom separations. We illustrate numerically how this interaction between oxygen, sulphur, hydrogen, or nitrogen atom pairs may turn repulsive near water droplets. The results provide evidence of a mechanism causing excited state atom pair breakage to occur in the atmosphere near water droplets.

Zero-index metamaterials with near-zero permittivity and/or permeability usually reflect oblique incident waves due to total reflection that occurs at the air-metamaterial interface. In this work, we show that if one component of the near-zero–permittivity tensor of metamaterial turns from positive to negative due to a small disturbance, the dispersion surface changes dramatically from a tiny circle to a hyperbola, which enables oblique transmissions. A series of high-order total-transmission peaks at large incident angles is predicted and observed. These peaks are induced by Fabry-Pérot effects. Our work may have potential applications for filters, sensors and switches.

The rectification of light beams in an optical ratchet is reported. This directed transport is implemented using a photonic mesh lattice consisting of sequences of directional couplers. In such a structure, we observe light propagation at an angle that is independent of the input direction of the injected beam.

We consider a statically compressed diatomic granular crystal, consisting of alternating aluminum and steel spheres. The combination of dissipation, driving of the boundary, and intrinsic nonlinearity leads to complex dynamics. Through both numerical simulations and experiments, we find that the interplay of nonlinear surface modes with modes caused by the driver create the possibility, as the driving amplitude is increased, of limit cycle saddle-node bifurcations beyond which the dynamics of the system becomes chaotic. In this chaotic state, part of the applied energy can propagate through the chain. We also find that the chaotic branch depends weakly on the driving frequency, and speculate a connection between the chaotic dynamics with the gap openings between the spheres. Finally, we observe hysteretic dynamics and an interval of multi-stability involving stable periodic solutions and chaotic ones.

The electromagnetically induced Talbot effect (EITE) offers a nondestructive and lensless way to image ultracold atoms or molecules (Wen J. M. et al., Appl. Phys. Lett., 98 (2011) 081108). We study an atomic imaging scheme based on the second-order two-photon EITE. Entangled photon pairs are taken as the imaging light to realize coincidence recording. Compared to the previous self-imaging scheme, the present one has the characteristic of imaging nonlocally and of the controllable image variation in size, and thus, it is useful for facilitating the EITE application in imaging techniques.

The electromagnetically driven liquid metal flow in a toroidal duct of a square cross-section is studied numerically searching for the critical Reynolds (Re) and Hartmann (Ha) numbers where transition occurs. Results are reported for Ha up to 500, building a transition map of critical Reynolds and Hartmann numbers and showing two distinct regimes of transition signified by the destabilization of the secondary flow: The first, for Ha < 18, where the Lorentz force is balanced by fluid momentum diffusion and the second, for Ha ⩾ 18, where it is balanced by fluid inertia. In both cases, the destabilization of the secondary flow occurs primarily near the concave sidewall. For Ha ⩾ 18 the transition follows approximately the relationship Re = 16.803 Ha^1.43 for values of Re and Ha in the range 80 < Re/Ha < 224.

We present an orthotropic elastic analysis of frictional granular layers under gravity by studying their stress response to a localized overload at the layer surface for several substrate tilt angles. The distance to the unjamming transition is controlled by the tilt angle α with respect to the critical angle α_c. We find that the shear modulus of the system decreases with α, but reaches a finite value as α → α_c. We also analyze the vibration modes of the system and show that the soft modes play an increasing, though not crucial, role approaching the transition.

If an inextensible thin sheet adheres to a substrate with a negative Gaussian curvature, it will experience stress due to geometric frustration. We analyze the consequences of such geometric frustration using analytic arguments and numerical simulations. Both concentric wrinkles and eye-like folds are shown to be compatible with negative curvatures. Which pattern will be realized depends on the curvature of the substrate. We discuss both types of folding patterns and determine the phase diagram governing their appearance.

Recently, an active microswimmer was constructed where a micron-sized droplet of bromine water was placed into a surfactant-laden oil phase. Due to a bromination reaction of the surfactant at the interface, the surface tension locally increases and becomes non-uniform. This drives a Marangoni flow which propels the squirming droplet forward. We develop a diffusion-advection-reaction equation for the order parameter of the surfactant mixture at the droplet interface using a mixing free energy. Numerical solutions reveal a stable swimming regime above a critical Marangoni number M but also stopping and oscillating states when M is increased further. The swimming droplet is identified as a pusher whereas in the oscillating state it oscillates between being a puller and a pusher.

A steam plasma jet (SPJ) by using both water and 1,4-dioxane aqueous solution (DAS) as working medium was injected into contaminated water to decompose 1,4-dioxane. The optical emission spectroscopy analysis showed that the formation of the excited species CH* and C₂^* depended on the concentration of 1,4-dioxane. The influences of SPJ gas temperatures for different working mediums were discussed. The 1,4-dioxane decomposition was enhanced when DAS was used as working medium and SPJ was injected into DAS. Synthesis gas (a mixture of H₂ and CO) and CO₂ were the main products in gaseous effluents.

Nanosecond-pulse surface dielectric barrier discharge is a promising method used for airflow control application. In our letter, atmospheric-pressure plasmas in open air are produced in a configuration of discharge actuators by repetitive nanosecond pulses. The electrical parameters including applied voltage, total discharge current, and transported charge are measured and analysed, especially it is aimed at the time behaviour of the total discharge current. Experimental results show that the total discharge current pulse includes two obvious spikes during the rise time of the applied pulse voltage. According to the simulation, it is concluded that the first current spike is due to the discharge propagation in the form of wave ionization and displacement current. The second current spike is caused by the repeated re-ignition of the surface dielectric barrier discharge on the area covered previously by the wave ionization.

Transport properties of F⁻ ions in F₂ in DC fields were calculated using the Monte Carlo simulation technique. In the absence of a more reliable theory or experiments we have employed a simple technique to predict the cross-sections and to separate elastic from reactive collisions. We present reaction rate coefficients, characteristic energies, mean energy and drift velocities for the conditions of low and moderate reduced electric fields E/N (E is the electric field, N the gas density) accounting also for the non-conservative collisions.

The thermally vibrational properties of icosahedral (ICH) and face-center-cubic (FCC) copper nanoclusters have been compared by carrying out molecular dynamics simulations with a local-environment-dependent tight-binding potential. Although both ICH and FCC copper nanoclusters exhibit a low- and high-energy enhancement of vibrational density of states (VDOS) in comparison with the bulk copper, the vibrational properties of nanoclusters show a strong structure-dependent feature. The different structure is revealed to result in the different atom package, the different lattice shrinkage, the different local pressure, and thus the different VDOS. The different atom package at the surfaces of clusters is responsible for the different low-energy VDOS in a different power-law behavior between the FCC and ICH clusters. The lattice contraction and the internal pressure in the sense of the bulk are unified to explain the enhanced high-energy tail in the VDOS of FCC clusters, but not in the case of ICH clusters.

Pressure-induced effects on elastic, structural phase transition and mechanical properties of TiC and TiN are studied under high pressures from first-principle calculations. Calculated lattice parameters, elastic constants and theoretical Vickers hardness are in excellent agreement with available experimental and theoretical results. The transition pressure from NaCl to CsCl phase is determined with values of 5.695 Mbar for TiC and 3.482 Mbar for TiN. Pressure-induced effects on mechanical properties of NaCl-type TiC and TiN show that the Vickers hardness increases first, to a maximum value 43.65 and 27.48 GPa at the pressure of 2.1 and 0.9 Mbar for NaCl-type TiC and TiN, respectively, and then decreases with increasing pressure.

The restricted primitive model with nonadditive hard-sphere diameters is shown to have interesting and peculiar clustering properties. We report accurate calculations of the cluster concentrations. Implementing efficient and ad hoc Monte Carlo algorithms we determine the effect of nonadditivity on both the clustering and the gas-liquid binodal. For negative nonadditivity, tending to the extreme case of completely overlapping unlike ions, the prevailing clusters are made of an even number of particles having zero total charge. For positive nonadditivity, the frustrated tendency to segregation of like particles and the reduced space available to the ions favors percolating clusters at high densities.

By using modern materials growth techniques such as molecular beam epitaxy, a tunable δ-potential can be intentionally doped into semiconductor nanostructures. In this work, we theoretically investigate modulation of electron-spin polarization by such a δ-doping in a hybrid ferromagnet and semiconductor nanostructure, where a nanosized ferromagnetic stripe with horizontal magnetization is deposited on top of a semiconductor heterostructure. It is shown that this nanosystem possesses a considerable spin polarization effect due to breaking the intrinsic symmetry by the δ-doping. It is also shown that both magnitude and sign of spin polarization vary dramatically with the height and/or position of the δ-doping. These interesting properties may provide an alternative scheme to achieve a controllable spin-polarized source, and this nanostructure may serve as a structurally tunable spin filter.

Using the density-functional perturbation theory with structural optimization, we investigate the electronic structure, phonon spectra, and superconductivity of the BiS₂-based layered compounds LaO_1−xF_xBiS₂. For LaO_0.5F_0.5BiS₂, the calculated electron-phonon coupling constant is equal to λ = 0.8, and the obtained T_c ≃ 9.1 K is very close to its experimental value, indicating that it is a conventional electron-phonon superconductor.

Band ferromagnetism in strongly correlated electron systems is one of the most challenging issues in today's condensed-matter physics. In this theoretical work, we study the competition between kinetic term, Coulomb repulsion, and on-site correlated disorder for various lattice geometries. Unconventional and complex ferromagnetic phase diagrams are obtained: wide region of stability, cascade of transitions, re-entrance, high sensitivity to the carrier concentration and strongly inhomogeneous ground states for relatively weak on-site potential. The direct and systematic comparison with exact diagonalization shows that the unrestricted Hartree-Fock method is unexpectedly accurate for such systems, which allows large-size cluster calculations. A match of the order of 99.9% for weak and intermediate couplings is found, slightly reduced to about 95% in the large-repulsion regime. Nano-patterned lattices appear to be particularly promising candidates that could, with the tremendous progress in growing and self-organized techniques, be synthesized in the near future.

High-temperature superconducting copper oxides display a variety of both long-range and local lattice anomalies which are related to the onset of the pseudogap phase and / or the onset of superconductivity. Here we show that these anomalies demonstrate polaron formation where specifically the local character of the polarons plays an important role. We predict that unconventional isotope effects will appear in both the long-wavelength and local lattice effects.

We investigated the fabrication process of a nanostructure with alumina insulator layer and nanoscale Cu paths punching through an alumina layer inserted between magnetic multilayers. Ion-beam–assisted oxidation was applied to an AlCu layer, where ion beams with three kinds of noble gases of different mass, Ne, Ar and Xe, were compared. The heavy gas overcame the trade-off between the increasing purity of nanoscale Cu paths and the decreasing oxygen defects of the alumina. It is considered that the high mobility of surface atoms in the AlCu layer brought about by the heavy-gas ion beam promotes segregation of alumina and Cu.

It is well known that the quantum correction to the conductivity in graphene may show a transition from weak-localization to weak-antilocalization regime. We develop a non-diffusion theory of the weak localization in graphene and consider the interplay between weak antilocalization due to intravalley scattering and weak localization due to intervalley scattering of electrons. The switch between the two regimes may be observed as the "metal-insulator" transition in the temperature dependence of the conductivity for the metallic regime corresponding to fast interalley transitions and the insulator regime corresponding to slow intravalley transitions.

We study the response of quantum many-body systems to coupling some of their degrees of freedom to external gauge fields. This serves to understand the current Green functions and transport properties of interacting many-body systems. Our analysis leads to a "gauge theory of states of matter" complementary to the well-known Landau theory of order parameters. We illustrate the power of our approach by deriving and interpreting the gauge-invariant effective actions of (topological) superconductors, 2D electron gases exhibiting the quantized Hall- and spin-Hall effect, 3D topological insulators, as well as axion electrodynamics. We also use the theory to elucidate the structure of surface modes in these systems.

We theoretically study the heat generation induced by the electric current in a quantum dot coupled to a normal and a superconducting lead with weak dot-leads coupling. We find that the heat generation presents quite different properties from the current and can be controlled by the gate voltage, bias and temperature. At zero temperature, there are many ideal regions for device operation with large electric current and small heat generation. Interestingly, at high temperature, the heat generation can become negative in the regions where the phonon-assisted Andreev tunneling and phonon-assisted direct tunneling with absorbing a phonon can occur. This means such a device can serve as a refrigerator.

A novel spectral algorithm utilizing multiple eigenvectors is proposed to identify the communities in networks based on the modularity Q. We investigate the reduced modularity on low-rank approximations of the original modularity matrix consisting of leading eigenvectors. By exploiting the rotational invariance of the reduced modularity, near-optimal partitions of the network can be found. This approach generalizes the conventional spectral network partitioning algorithms which usually use only one eigenvector, and promises better results because more spectral information is used. The algorithm shows excellent performance on various real-world and computer-generated benchmark networks, and outperforms the most known community detection methods.

A simple model for evaluating the thermal atomic transfer rates in nanosystems (Lin Z.-Z. et al., EPL, 94 (2011) 40002) was developed to predict the chemical reaction rates of nanosystems with small gas molecules. The accuracy of the model was verified by MD simulations for molecular adsorption and desorption on a monatomic chain. By the prediction, a monatomic carbon chain should survive for 1.2 × 10² years in the ambient of 1 atm O₂ at room temperature, and it is very invulnerable to N₂, H₂O, NO₂, CO and CO₂, while a monatomic gold chain quickly ruptures in vacuum. It is worth noting that since the model can be easily applied via common ab initio calculations, it could be widely used in the prediction of chemical stability of nanosystems.

The dynamics of a self-propelled Brownian sphere confined between two planar hard walls is investigated by computer simulations and analytic solutions of the corresponding Fokker-Planck equation. It is shown that an accumulation of self-propelled particles, often linked to the hydrodynamic dipole interaction, can be already obtained from the combination of Brownian motion and self-propulsion. The surface excess is calculated as a function of particle velocity, wall separation, and translational and rotational diffusion coefficients. In limits of narrow channels or small propulsion velocities, analytical solutions and numerical results are in excellent agreement.

It is known that an abstract model with linear and distance-dependent interactions can develop a topographic connection structure in an input-output two-layer system. We expand the model by reflecting the effects of correlations between propagating neural firings and investigate the emergent properties in the resulting nonlinear model. It is found that the output layer can separate into several ones between which topographic connections develop. This result shows that hierarchically differentiated cortical sections, developing on a lattice structure, can regulate their boundary through Hebbian plasticity. We further argue that the phenomenon of cortical area differentiation can be described as a kind of phase transition.

Constrained clustering has been well-studied in the unsupervised learning society. However, how to encode constraints into community structure detection, within complex networks, remains a challenging problem. In this paper, we propose a semi-supervised learning framework for community structure detection. This framework implicitly encodes the must-link and cannot-link constraints by modifying the adjacency matrix of network, which can also be regarded as de-noising the consensus matrix of community structures. Our proposed method gives consideration to both the topology and the functions (background information) of complex network, which enhances the interpretability of the results. The comparisons performed on both the synthetic benchmarks and the real-world networks show that the proposed framework can significantly improve the community detection performance with few constraints, which makes it an attractive methodology in the analysis of complex networks.