Multiple Devil's staircase in a discontinuous circle map

The multiple Devil's staircase, which describes phase-locking behavior, is observed in a discontinuous nonlinear circle map. Phase-locked steps form many towers with similar structure in winding number(W)-parameter(k) space. Each step belongs to a certain period-adding sequence that exists in a smooth curve. The Collision modes that determine steps and the sequence of mode transformations create a variety of tower structures and their particular characteristics. Numerical results suggest a scaling law for the width of phase-locked steps in the period-adding (W=n/(n+i), n,i∈int) sequences, that is, Δk(n)∝n^-τ (τ>0). And the study indicates that the multiple Devil's staircase may be common in a class of discontinuous circle maps.     

Strain versus stress in a model granular material: A Devil's staircase

The series of equilibrium states reached by disordered packings of rigid, frictionless disks in two dimensions, under gradually varying stress, are studied by numerical simulations. Statistical properties of trajectories in configuration space are found to be independent of specific assumptions ruling granular dynamics, and determined by geometry only. A monotonic increase in some macroscopic loading parameter causes a discrete sequence of rearrangements. For a biaxial compression, we show that, due to the statistical importance of such events of large magnitude, the dependence of the resulting strain on stress direction is a Levy flight in the thermodynamic limit.     

Devil's staircase in three-dimensional coherent waves localized on Lissajous parametric surfaces

We experimentally demonstrate the significance of the longitudinal-transverse coupling in the mesoscopic regime by using a high-Q laser resonator as an analog experiment. The longitudinal-transverse coupling is found to lead to the three-dimensional (3D) coherent waves that are localized on the parametric surfaces with Lissajous transverse patterns. More strikingly, experimental results reveal that the mode locking of the 3D coherent states forms a nearly complete Devil's staircase with the hierarchical ordering.     

"Devil's staircase" in Pb/Si(111) ordered phases

With scanning tunneling microscopy we have found that ordered phases in Pb/Si(111) are one of the best examples of the "devil's staircase" phase diagram. Phases within a narrow coverage range (1.2相似文献   

"Devil's staircase"-type phase transition in NaV2O5 under high pressure

The "devil's staircase"-type phase transition in the quarter-filled spin-ladder compound NaV2O5 has been discovered at low temperature and high pressure by synchrotron radiation x-ray diffraction. A large number of transitions are found to successively take place among higher-order commensurate phases with 2a x 2b x zc type superstructures. The observed temperature and pressure dependence of modulation wave number q(c), defined by 1/z, is well reproduced by the axial next nearest neighbor Ising model. The q(c) is suggested to reflect atomic displacements presumably coupled with charge ordering in this system.     

Coherent electron transport in a helical nanotube

The quantum dynamics of carriers bound to helical tube surfaces is investigated in a thin-layer quantization scheme. By numerically solving the open-boundary Schrödinger equation in curvilinear coordinates, geometric effect on the coherent transmission spectra is analysed in the case of single propagating mode as well as multimode. It is shown that, the coiling endows the helical nanotube with different transport properties from a bent cylindrical surface. Fano resonance appears as a purely geometric effect in the conductance, the corresponding energy of quasibound state is obviously influenced by the torsion and length of the nanotube. We also find new plateaus in the conductance. The transport of double-degenerate mode in this geometry is reminiscent of the Zeeman coupling between the magnetic field and spin angular momentum in quasi-one-dimensional structure.     

Equilibrium states for a plane incompressible perfect fluid

We associate to the plane incompressible Euler equation with periodic conditions the corresponding Hopf equation, as an equation for measures on the space of solenoidal distributions. We define equilibrium states as the solutions of the stationary Hopf equation. We find a class of equilibrium states which corresponds to a class of infinitely divisible distributions, and investigate the properties of gaussian and poissonian states. Equilibrium dynamics for a class of poissonian states is constructed by means of the Onsager vortex equations.Research partially supported by C.N.R., G.N.F.M.     

Fractional quasiexcitons in incompressible electron liquids

A new kind of many-body excitonic state composed of fractionally charged constituents is introduced. The constituents are a trion (X^-) embedded in an incompressible electron liquid and Laughlin quasiholes (QH's). Laughlin electron–trion correlations lead to an effective trion charge of -e/3. This many-body excitation is called “quasiexciton” and denoted by to distinguish it from a normal trion. The can bind one or two (e/3)-charged QH's, giving a neutral or a positive . The energy spectra and photoluminescence from radiative quasiexciton decay are studied numerically and interpreted using a generalized composite Fermion model of the e–X^- fluid.     

Dielectric properties of a magnetized electron gas in a nanotube

A quantum expression is derived for the longitudinal permittivity of a magnetized electron gas in a quantum cylinder. The asymptotics of the dispersion law are calculated for longitudinal plasma waves in a degenerate electron gas. The approximations of the weak and strong spatial dispersions are considered. It is shown that the longitudinal permittivity is an oscillating function of the magnetic flux through the cross section of the nanotube.     

Low-energy electron transmission in a partially unzipped zigzag nanotube

Based on the nearest-neighbor tight-binding approximation, we present exact analytical expressions for electron transmission in nanotube/ribbon junctions, generated by incomplete unzipping of zigzag nanotubes. By assuming one-dimer-line difference in the widths of the leads, it is demonstrated that such a contact exhibits zero backscattering of low-energy electrons entering from the graphene side of the junction. We also show that a zigzag nanotube section sandwiched between two armchair graphene ribbons is completely transparent for incident low-energy electrons. Possible application of the results to nanosensor engineering is also included.     

Quantum interference in nanotube electron waveguides

We have calculated the quantum conductance of single-walled carbon nanotube (SWNT) waveguide by using a tight binding-based Greens function approach. Our calculations show that the slow conductance oscillations as well as the fast conductance oscillations are manifestations of the intrinsic quantum interference properties of the conducting SWNTs, being independent of the defect and disorder of the SWNTs. And zigzag type tubes do not show the slow oscillations. The SWNT electron waveguide is also found to have distinctly different transport behavior depending on whether or not the length of the tube is commensurate with a (3N+1) rule, with N the number of basic carbon repeat units along the nanotube length.     

Capacitance spectroscopy of compressible and incompressible stripes in a narrow electron channel

We study the capacitance of single electron wires in high quantizing magnetic fields. The capacitance spectra obtained on 300 nm wide electron channels are interpreted with a simple model considering the geometry of the incompressible stripes in the electron channel as function of filling factor. The capacitance spectra directly reflect the potential form of the wire edge. This is experimentally demonstrated by the dependence on the confinement potential as well as by a clear asymmetry of the capacitance minimum at filling factor v=2 that can be well explained with the model. For comparison we present capacitance spectra obtained on very narrow, but otherwise similar quantum wires, in which quantization into one-dimensional subbands dominates the behavior.     

Spontaneous decay of excited atomic states near a carbon nanotube

The spontaneous decay process of an excited atom placed inside or outside a carbon nanotube is analyzed. Calculations have been performed for various achiral nanotubes. The effect of the nanotube surface is shown to increase the atomic spontaneous decay rate by up to 6 orders of magnitude compared with that of the same atom in vacuum. This increase is associated with nonradiative decay via surface excitations in the nanotube.     

Intersubband electron transition across a staircase potential containing quantum wells: light emission

We present a theoretical investigation of a novel staircase-like light emitter based on the GaAs/Ga_xAl_1−xAs material system. The emission wavelength is around 12 μm. The device operation is based on the intersubband bound-to-bound transition. The energy band profile of the structure has been solved self-consistently. We have also calculated the oscillator strength.     

Strongly localized states in a single carbon nanotube with polymer molecules

A single-walled carbon nanotube (SWCNT) with conjugated polymer molecules is analyzed via optical spectroscopy. The presence of strongly localized excitonic states in the SWCNT is confirmed using time-integrated photoluminescence (PL). The PL spectrum exhibits extremely narrow width (~0.8 meV) which is attributed to the strong confinement of the states by polymer molecules. In addition, I observed that the excited states are gradually filled as a function of the excitation power, which supports the localized excitonic behavior. Only the ground excitonic state is observed at low excitation powers, but three additional PL peaks appear as the excitation power is increased. Especially, the power-dependent PL spectrum shows a blueshift and increased width, which can be elucidated in terms of quantum confined stark effect and the screening of induced electric fields. Overall, I demonstrate that the presence of polymer molecules induces several localized states in a single SWCNT.     

Coherent states of a free electron laser

We define electron-field coherent quasi-classical states of a free electron laser. In these states both the photon number and the electron momentum are given by a Poisson distribution centered on the classical trajectories.     

Dynamical two electron states in a Hubbard-Davydov model

We study a model in which a Hubbard Hamiltonian is coupled to the dispersive phonons in a classical nonlinear lattice. Our calculations are restricted to the case where we have only two quasi-particles of opposite spins, and we investigate the dynamics when the second quasi-particle is added to a state corresponding to a minimal energy single quasi-particle state. Depending on the parameter values, we find a number of interesting regimes. In many of these, discrete breathers (DBs) play a prominent role with a localized lattice mode coupled to the quasiparticles. Simulations with a purely harmonic lattice show much weaker localization effects. Our results support the possibility that DBs are important in HTSC.Received: 14 August 2004, Published online: 26 November 2004PACS: 71.38.-k Polarons and electron-phonon interactions - 63.20.Pw Localized modes - 63.20.Ry Anharmonic lattice modes