Metamaterial composed of wire pairs exhibiting dual band negative refraction

The design of the metamaterial that can exhibit negative refraction at two frequency bands is presented. The components of this metamaterial are cut wire pairs and continuous wires. The cut wire pairs structure in our sample can achieve the magnetic resonance at two frequency bands by appropriately designing the cut wire dimension. Through numerical simulation, the transmission property of the proposed dual band negative index metamaterial is investigated and its result shows that with the introduction of continuous wires, the stop bands for cut wire pairs (permeability μ<0) and the frequency band for continuous wires (permittivity ε<0) components would overlap and lead to the appearance of pass bands near the two magnetic resonance frequency bands. Its electromagnetic properties are then retrieved to demonstrate that the dual band left-hand behavior can be obtained in our sample structure. It is believed that our approach will be effective to make this kind of dual band negative refractive metamaterial based on the multiple magnetic resonances work at optical frequency.     

Positive and negative refraction of magnetoinductive waves in two dimensions

Previous studies of magnetoinductive waves in homogeneous media with resonant elements consisting of capacitively loaded metallic loops are extended to the case when a single wave from one medium is incident upon another one. The relationship between the input and output angles and the reflection and transmission coefficients are determined with the aid of the dispersion equation for different scenarios. An expression is obtained for the power density vector, and it is shown that its component perpendicular to the boundary is conserved across the boundary. Using different configurations of the elements it is shown that both positive and negative refraction may occur.     

Confinement of static quarks in two dimensional lattice gauge theories

In two dimensional Higgs models on a lattice with Abelian or Nonabelian compact gauge group, fractional static charges are always confined.     

Nuclear spin ferromagnetic phase transition in an interacting two dimensional electron gas

Electrons in a two-dimensional semiconducting heterostructure interact with nuclear spins via the hyperfine interaction. Using a a Kondo lattice formulation of the electron-nuclear-spin interaction, we show that the nuclear-spin system within an interacting two-dimensional electron gas undergoes a ferromagnetic phase transition at finite temperatures. We find that electron-electron interactions and non-Fermi liquid behavior substantially enhance the nuclear-spin Curie temperature into the mK range with decreasing electron density.     

On negative refraction in electron optics

Negative refraction is investigated within the context of both relativistic and non-relativistic electron optics. In fact, starting from the de Broglie wave-particle dualism, the negative refractive index as a function of wavelength is determined for both relativistic and non-relativistic electrons. Comparison with photon optics is done. Negative refractive index averaged over both sufficiently small and sufficiently large wavelength ranges is found to be tending to minus unity and minus infinity, respectively. In addition, the sensitivity to wavelength of the negative refractive index is evaluated.     

Chemical diffusion in a one dimensional lattice with two sites inequivalent2

Making use of the exact form of the Nernst-Einstein equation and an exact expression for the d.c. ionic conductivity derived by Richards, I have derived an exact expression for the chemical diffusion coefficient in a one dimensional lattice with two sites inequivalent and self-blocking by the atoms. It was found that the chemical diffusion coefficient is independent of concentration. This particular result, however, can apply only to the one dimensional lattice.     

On the symmetry of the Gibbs states in two dimensional lattice systems

Under fairly general conditions if a two dimensional classical lattice system has an internal symmetry groupG, which is a compact connected Lie group, then all Gibbs states areG-invariant.     

Large negative lateral shifts due to negative refraction

When a thin structure in which negative refraction occurs (a metallo-dielectric structure or a photonic crystal) is illuminated by a beam, the reflected and transmitted beam can undergo a large negative lateral shift. This phenomenon can be seen as an interferential enhancement of the geometrical shift and can be considered a signature of negative refraction.     

Instabilities of weakly correlated electronic gas on a two dimensional lattice

We use the Kadanoff-Wilson renormalization group to find the instabilities of the two dimensional Hubbard model in the weak coupling limit. Starting from the full bandwidth, we reduce the energy cutoff for fermions and derive the low-energy effective action. If the filling is enough far from one half, the effective low-energy theory is BCS and there exists a mean-field like superconducting instability with D-wave order parameter. Close to the half-filling, the effective low-energy theory is parquet and the dominant fluctuations at the critical temperature are antiferromagnetic.     

单轴晶体中负折射现象的演示

用惠更斯作图法定性地说明了单轴晶体中负折射现象产生的基本原理,演示了YVO4晶体中发生的负折射现象.该实验有助于学生全面认识折射现象.     

Spin orbit coupled Bose Einstein condensate in a two dimensional bichromatic optical lattice

We numerically investigate the localization of Bose Einstein condensate (BEC) with spin orbit coupling in a two dimensional bichromatic optical lattice. We study localization in weakly interacting and non-interacting regimes. The existence of stationary localized states in the presence of spin–orbit and Rabi couplings has been confirmed. We find that spin orbit coupling favors localization, whereas Rabi coupling has a slight delocalization effect.     

Three dimensional dynamics of ferromagnetic swimmer

It is shown that a flexible ferromagnetic filament self-propels perpendicularly to the AC magnetic field during a limited period of time due to the instability of the planar motion with respect to three dimensional perturbations. The transition from the oscillating U-like shapes to the oscillating S-like shapes is characterized by the calculated Wr number.     

Efficient tunable negative refraction photonic crystal achieved by an elliptic rod lattice with a nematic liquid crystal

Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. We have investigated the electromagnetic wave propagation inside an elliptic rod PC slab by means of finite-difference time-domain simulations. The band structure of the PC composed of elliptic rod in the square and triangular lattices is studied by solving Maxwell's equations using the plane wave expansion method. Numerical simulations show that the refractive angle can be tuned greatly by rotating the directors of elliptic rod in the PC slab. Furthermore, an optical switch based on elliptic rod PC structures with nematic liquid crystals was proposed. In the on/off switching system, the partial band gap can be controlled when the normalized operation frequency is 0.28. The modulation induced by liquid crystals created a sharp switching in the photonic devices. Such a mechanism of negative refraction PCs should open up a new application for designing components in photonic integrated circuits.     

Spin liquid in an almost ferromagnetic Kondo lattice

A theory of stabilization of a spin liquid in a Kondo lattice at temperatures close to the temperature of antiferromagnetic instability has been developed. Kondo exchange scattering of conduction electrons leads to emergence of a state of the spin liquid of the resonating valence bonds (RVB) type at T>T _K. Owing to this stabilization, low-energy processes of Kondo scattering with energies below T _K are frozen so that the “singlet” state of the Kondo lattice is not realized; instead a strongly correlated spin liquid with developed antiferromagnetic fluctuations occurs. A new version of the Feynman diagram technique has been developed to describe interaction between spin fluctuations and resonant valence bonds in a self-consistent manner. Emergence of a strongly anisotropic RVB spin liquid is discussed. Zh. éksp. Teor. Fiz. 112, 729–759 (August 1997)     

Coexistence of antiferromagnetic and ferromagnetic phase for ferromagnetic Kondo lattice model

To study the proposed phase separations in doped manganites, we performed Monte-Carlo calculations for the ferromagnetic Kondo lattice model with strong Hund's coupling between conduction electrons and localized spins. For the practical calculations, we adopted a one dimensional lattice and treated the spins of the localized t_2g electrons semi-classically. A direct evidence of the phase separation is observed from a snapshot of the spatial dependence of localized spins. No indication of the canted or spiral phases is found in the results of simulations. Further, the calculated results of the spin structure factor in the phase separation region are well compared with recent experiments. Received: 1st September 1998 / Revised: 30 October 1998 / Accepted: 27 November 1998     

Thermodynamic studies of the two dimensional Falicov-Kimball model on a triangular lattice

Thermodynamic properties of the spinless Falicov-Kimball model are studied on a triangular lattice using numerical diagonalization technique with Monte-Carlo simulation algorithm. Discontinuous metal-insulator transition is observed at finite temperature. Unlike the case of square lattice, here we observe that the finite temperature effect is not able to smear out the discontinuous metal-insulator transition seen in the ground state. Calculation of specific heat (C _v ) shows single and double peak structures for different values of parameters like on-site correlation strength (U), f-electron energy (E _f ) and temperature.     

Ultrasonic band gaps and negative refraction

The first experimentally observed ultrasonic band gaps in periodic bidimensional composited are reviewed here. The studied basic structure consists of an aluminum alloy plate with a periodic arrangement of cylindrical holes filled with mercury. Localization phenomena in linear and point defects have been observed and an ultrasonic waveguide capable to bend the ultrasonic radiation by 90 degrees has been achieved. We also revisit twinned-square periodic structures for ultrasonic wave bending and splitting. Such devices allow 45 degrees bending of waves, whereas an extreme anomalous refraction law at the grain boundaries has also been experimentally observed. Finally, a preliminary study about the possibility of "left-handed" behaviour in ultrasonic crystals is presented in this work. The device consists of a slab of the above mentioned metallic composite attached to an epoxy wedge. In this system, clues to negative refraction are theoretically shown.     

The two dimensional classical anisotropic Heisenberg ferromagnetic model with nearest- and next-nearest neighbor interactions

We use the self-consistent harmonic approximation (SCHA) to study the two-dimensional classical Heisenberg anisotropic (easy-plane) ferromagnetic model including nearest- and next-nearest neighbor exchange interactions. For temperatures much lower than the Kosterlitz-Thouless phase transition temperature T _KT, spin waves must be the most relevant excitations in the system and the SCHA must account for its behavior. However, for temperatures near T _KT, we should expect vortex pairs to be quite important. The effect of these vortex excitations on the phase transition temperature is included in our theory as a renormalization of the exchange interactions. Then, combining the SCHA theory to the renormalization effect due to vortex pairs, we calculate the dependence of T _KT as a function of the easy-plane anisotropies and exchange interactions. Received 3 April 2001 and Received in final form 20 September 2001