Resonances, instabilities, and structure selection of driven josephson lattice in layered superconductors

We investigate the dynamics of the Josephson vortex lattice in layered high- T(c) superconductors at high magnetic fields. It is shown that the average electric current depends on the lattice structure and is resonantly enhanced when the Josephson frequency matches the frequency of the plasma mode. We find the stability regions of a moving lattice. It is shown that a specific lattice structure at a given velocity is uniquely selected by the boundary conditions; at small velocities a periodic triangular lattice is stable and looses its stability at some critical velocity. At even higher velocities, a structure close to a rectangular lattice is restored.     

A method for measuring the Witten index using lattice simulation

We propose a method to measure the Witten index using lattice simulation. A requirement for the lattice model is that it has at least one exact supersymmetry at finite lattice spacing. We prove the validity of the method in case of the supersymmetric quantum mechanics, where the index is well known.     

Magic Wavelength Measurement of the ~(87)Sr Optical Lattice Clock at NIM

We report on the magic wavelength measurement of our optical lattice clock based on fermion strontium atoms at the National Institute of Metrology(NIM).A Ti:sapphire solid state laser locked to a reference cavity inside a temperature-stabilized vacuum chamber is employed to generate the optical lattice.The laser frequency is measured by an erbium fiber frequency comb.The trap depth is modulated by varying the lattice laser power via an acousto-optic modulator.We obtain the frequency shift coefficient at this lattice wavelength by measuring the differential frequency shift of the clock transition of the strontium atoms at different trap depths,and the frequency shift coefficient at this lattice wavelength is obtained.We measure the frequency shift coefficients at different lattice frequencies around the magic wavelength and linearly fit the measurement data,and the magic wavelength is calculated to be 368554672(44) MHz.     

Atoms in a radio-frequency-dressed optical lattice

We load cold atoms into an optical lattice dramatically reshaped by radio-frequency coupling of state-dependent lattice potentials. This radio-frequency dressing changes the unit cell of the lattice at a subwavelength scale, such that its curvature and topology departs strongly from that of a simple sinusoidal lattice potential. Radio-frequency dressing has previously been performed at length scales from mm to tens of mum, but not at the single-optical-wavelength scale. At this length scale significant coupling between adiabatic potentials leads to nonadiabatic transitions, which we measure as a function of lattice depth and dressing amplitude. We also investigate the dressing by measuring changes in the momentum distribution of the dressed states.     

Exciton condensation driving the periodic lattice distortion of 1T-TiSe2

We address the lattice deformation of 1T-TiSe2 within the exciton condensate phase. We show that, at low temperature, condensed excitons influence the lattice through electron-phonon interaction. It is found that at zero temperature, in the exciton condensate phase of 1T-TiSe2, this exciton condensate exerts a force on the lattice generating ionic displacements comparable in amplitude to what is measured in experiment. This is thus the first quantitative estimation of the amplitude of the periodic lattice distortion observed in 1T-TiSe2 as a consequence of the exciton condensate phase.     

Non-perturbative renormalization of lattice four-fermion operators without power subtractions

A general nonperturbative analysis of the renormalization properties of four-fermion operators in the framework of lattice regularization with Wilson fermions is presented. We discuss the nonperturbative determination of the operator renormalization constants in the lattice regularization independent (RI or MOM) scheme. We also discuss the determination of the finite lattice subtraction coefficients from Ward identities. We prove that, at large external virtualities, the determination of the lattice mixing coefficients, obtained using the RI renormalization scheme, is equivalent to that based on Ward identities, in the continuum and chiral limits. As a feasibility study of our method, we compute the mixing matrix at several renormalization scales, for three values of the lattice coupling , using the Wilson and tree-level improved SW-Clover actions. Received: 26 February 1999 / Published online: 15 July 1999     

Systematics of collective correlation energies from self-consistent mean-field calculations

We study nucleon-nucleon scattering on the lattice at next-to-leading order in chiral effective field theory. We determine phase shifts and mixing angles from the properties of two-nucleon standing waves induced by a hard spherical wall in the center-of-mass frame. At fixed lattice spacing we test model independence of the low-energy effective theory by computing next-to-leading-order corrections for two different leading-order lattice actions. The first leading-order action includes instantaneous one-pion exchange and same-site contact interactions. The second leading-order action includes instantaneous one-pion exchange and Gaussian-smeared interactions. We find that in each case the results at next-to-leading order are accurate up to corrections expected at higher order.     

Incommensurate superfluidity of bosons in a double-well optical lattice

We study bosons in the first excited Bloch band of a double-well optical lattice, recently realized at NIST. By calculating the relevant parameters from a realistic nonseparable lattice potential, we find that in the most favorable cases, the boson lifetime in the first excited band can be several orders of magnitude longer than the typical nearest-neighbor tunneling time scales, in contrast with that of a simple single-well lattice. In addition, for sufficiently small lattice depths, the excited band has minima at nonzero momenta incommensurate with the lattice period, which opens a possibility to realize an exotic superfluid state that spontaneously breaks the time-reversal, rotational, and translational symmetries. We discuss possible experimental signatures of this novel state.     

Reversible random sequential adsorption of dimers on a triangular lattice

We report on simulations of reversible random sequential adsorption of dimers on three different lattices: a one-dimensional lattice, a two-dimensional triangular lattice, and a two-dimensional triangular lattice with the nearest neighbors excluded. In addition to the adsorption of particles at a rate K+, we allow particles to leave the surface at a rate K-. The results from the one-dimensional lattice model agree with previous results for the continuous parking lot model. In particular, the long-time behavior is dominated by collective events involving two particles. We were able to directly confirm the importance of two-particle events in the simple two-dimensional triangular lattice. For the two-dimensional triangular lattice with the nearest neighbors excluded, the observed dynamics are consistent with this picture. The two-dimensional simulations were motivated by measurements of Ca2+ binding to Langmuir monolayers. The two cases were chosen to model the effects of changing pH in the experimental system.     

用XRD和ACS测量研究Y1-xEuxBa2Cu3O7-δ超导体的应力钉扎机制

利用X射线衍射（XRD）和交流磁化率（ACχ）方法系统地研究了Y1x-EuxBa2Cu3O7-δ（x=0.0-1.0）超导体,研究发现Eu 掺杂替代了Y晶位后引起晶格失想与电流密度有密切的联系,对于不同掺杂成分样品,X射线衍射线分析表明（006）及（007）衍射峰型随掺杂量变化,杂浓度在30％和70％附近时,半高宽（FWHM)再现极大值,表明此时样品的晶格失配最大,与此相对应,电流密度Js也在此掺杂浓度范围内达到极大值,我们在晶格失配应力场的钉钆模型下对实现现象进行了讨论,认为Y1-xEuxBa2Cu3O7-δ超导体中由元素替代引起的晶格失配应力场是有效的钉扎中心。     

Near integrability of kink lattice with higher order interactions

We make use of Manton's analytical method to investigate the force between kinks and anti-kinks at large distances in 1+1 dimensional field theory.The related potential has infinite order corrections of exponential pattern,and the coefficients for each order are determined.These coefficients can also be obtained by solving the equation of the fluctuations around the vacuum.At the lowest order,the kink lattice represents the Toda lattice.With higher order correction terms,the kink lattice can represent one kind of generic Toda lattice.With only two sites,the kink lattice is classically integrable.If the number of sites of the lattice is larger than two,the kink lattice is not integrable but is a near integrable system.We make use of Flaschka's variables to study the Lax pair of the kink lattice.These Flaschka's variables have interesting algebraic relations and non-integrability can be manifested.We also discuss the higher Hamiltonians for the deformed open Toda lattice,which has a similar result to the ordinary deformed Toda.     

Condensate oscillations in a Penrose tiling lattice

We study the dynamics of a Bose-Einstein condensate subject to a particular Penrose tiling lattice. In such a lattice, the potential energy at each site depends on the neighbour sites, accordingly to the model introduced by Sutherland [16]. The Bose-Einstein wavepacket, initially at rest at the lattice symmetry center, is released. We observe a very complex time-evolution that strongly depends on the symmetry center (two choices are possible), on the potential energy landscape dispersion, and on the interaction strength. The condensate-width oscillates at different frequencies and we can identify large-frequency reshaping oscillations and low-frequency rescaling oscillations. We discuss in which conditions these oscillations are spatially bounded, denoting a self-trapping dynamics.     

Quantum phases in a resonantly interacting boson-fermion mixture

We consider a resonantly interacting boson-fermion mixture of 40K and 87Rb atoms in an optical lattice. We show that by using a red-detuned optical lattice the mixture can be accurately described by a generalized Hubbard model for 40K and 87Rb atoms, and 40K-87Rb molecules. The microscopic parameters of this model are fully determined by the details of the optical lattice and the interspecies Feshbach resonance in the absence of the lattice. We predict a quantum phase transition to occur in this system already at low atomic filling fraction, and present the phase diagram as a function of the temperature and the applied magnetic field.     

The S-FFT calculation of Collins formula and its application in digital holography

We study analytically and numerically the properties of one-dimensional chain of cold ions placed in a periodic potential of optical lattice and global harmonic potential of a trap. In close similarity with the Frenkel-Kontorova model, a transition from sliding to pinned phase takes place with the increase of the optical lattice potential for the density of ions incommensurate with the lattice period. We show that at zero temperature the quantum fluctuations lead to a quantum phase transition and melting of pinned instanton glass phase at large values of dimensional Planck constant. After melting the ion chain can slide in an optical lattice. The obtained results are also relevant for a Wigner crystal placed in a periodic potential.     

The macroscopic quantum phase of ultracold degenerate gases in the asymmetrical two-dimensional magnetic lattice

We investigate the existence of the macroscopic quantum phase in trapped ultracold quantum degenerate gases in an asymmetrical two-dimensional magnetic lattice. We show the key to adiabatically control the tunneling in the new two-dimensional magnetic lattice by means of external magnetic bias fields. In solving the system of coupled time-dependent differential equations, described here by the Boson Josephson Junctions (BJJs), we used an order parameter that includes both time-dependent variational parameters to describe the fractional population at each lattice site and the phase difference to quantify the macroscopic quantum phase signature. A dynamical oscillation of the fractional population and the phase difference at each individual lattice site is observed when solving the BJJs system.     

Soliton assisted control of source to drain electron transport along natural channels – crystallographic axes – in two-dimensional triangular crystal lattices

We present computational evidence of the possibility of fast, supersonic or subsonic,nearly loss-free ballistic-like transport of electrons bound to lattice solitons (a formof electron surfing on acoustic waves) along crystallographic axes in two-dimensionalanharmonic crystal lattices. First we study the structural changes a soliton creates inthe lattice and the time lapse of recovery of the lattice. Then we study the behavior ofone electron in the polarization field of one and two solitons with crossing pathways withsuitably monitored delay. We show how an electron surfing on a lattice soliton may switchto surf on the second soliton and hence changing accordingly the direction of its path.Finally we discuss the possibility to control the way an excess electron proceeds from asource at a border of the lattice to a selected drain at another border by followingappropriate straight pathways on crystallographic axes.     

Trapping and fusion of solitons in a nonuniform toda lattice

In this paper we consider strongly localized solitons leading to high energy events in a Toda lattice with springs of distinct nonlinearity. The trapping and superposition of solitons at a single soft spring embedded in a hard host lattice is investigated numerically. We further show the generation of high energy solitons at an interface between a hard and a soft lattice. The behaviour of a soliton incident on an inhomogeneity is approached analytically. The interaction of solitons in an inhomogeneous Toda lattice is compared to that in a homogeneous one.     

Surface solitons in chirped photonic lattices

We study surface modes at the edge of a semi-infinite chirped photonic lattice in the framework of an effective discrete nonlinear model. We demonstrate that the lattice chirp can change dramatically the conditions for the mode localization near the surface, and we find numerically the families of discrete surface solitons in this case. Such solitons do not require any minimum power to exist provided the chirp parameter exceeds some critical value. We also analyze how the chirp modifies the interaction of a soliton with the lattice edge.     

QCD sum rules,the spontaneous breakdown of chiral symmetry and short-distance behaviour in lattice gauge theories

We analyze the behaviour that correlation functions ought to have on the lattice in order to reproduce QCD sum rules in the continuum limit. We formulate a set of relations between lattice correlation functions of meson operators at small time separation and the quark condensates responsible for spontaneous breakdown of chiral symmetery. We suggest that the degree to which such relations are satisfied will provide a set of consistency checks on the ability of lattice Monte Carlo simulations to reproduce the correct spontaneous chiral symmetry breaking of the continuum theory.