Momentum distribution and condensate fraction of a fermion gas in the BCS-BEC crossover

By using the diffusion Monte Carlo method we calculate the one- and two-body density matrix of an interacting Fermi gas at T = 0 in the BCS to Bose-Einstein condensate (BEC) crossover. Results for the momentum distribution of the atoms, as obtained from the Fourier transform of the one-body density matrix, are reported as a function of the interaction strength. Off-diagonal long-range order in the system is investigated through the asymptotic behavior of the two-body density matrix. The condensate fraction of pairs is calculated in the unitary limit and on both sides of the BCS-BEC crossover.     

Damping of nuclear collective motion in the extended mean-field theory

The dissipation mechanism in slow nuclear collective motion is studied in the frame of the extended mean-field theory. The collective motion is treated explicitly by employing a travelling single-particle representation in the semi-classical approximation. The rate of change of the collective kinetic energy is determined by: (i) one-body dissipation, which reflects uncorrelated particle-hole excitations as a result of the collisions of particles with the mean field, (ii) two-body dissipation, which consists of simultaneous 2 particle-2 hole excitations via direct coupling of the residual two-body interactions, and (iii) potential dissipation due to the redistribution of the single-particle energies as a result of the random two-body collisions. In contrast to the first two processes the potential dissipation exhibits memory effects due to the large values of the local equilibration times.     

Small deviations from local equilibrium for a process which exhibits hydrodynamical behavior. I

The symmetric simple exclusion process where infinitely many particles move randomly on , jump with equal probability on nearest-neighbor sites, and interact by simple exclusion is considered. It is known that the only extremal invariant measures are Bernoulli, that each measure, in a suitable class, after a macroscopic time is locally described, at a zero-order approximation, by a Bernoulli measure with parameter depending on macroscopic space and time, and that the so-defined equilibrium profile satisfies the heat equation. Small deviations from local equilibrium in the hydrodynamical limit are investigated. It is proven, under suitable assumptions, that at first order the state is Gibbs with one- and two-body potentials whose strength depends only on macroscopic space and time and on the equilibrium profile. More precisely, the one-body potential is linear (on the microscopic positions of the particles) and proportional to the macroscopic space gradient of the equilibrium parameter at that time, so that Fourier law holds. The two-body potential varies on a macroscopic scale and does not depend on the microscopic positions of the particles; it is given by the value of the covariance of the Gaussian macroscopic density fluctuation field.     

The validity of the polynomial approximation to the solutions of the Vlasov equation

The validity of the polynomial variational approximation to the generator of the distribution function fluctuation is investigated in the context of the Vlasov equation applied to a simple model. The meaning of the Landau damping, or one-body dissipation is analysed.     

Phenomenological coefficients in a concentrated alloy for the dumbbell mechanism

We present an adaptation of the self-consistent mean field (SCMF) theory to calculate the transport coefficients in a concentrated alloy for diffusion by the dumbbell mechanism. In this theory, kinetic correlations are accounted for through a set of effective interactions within a non-equilibrium distribution function of the system. Transport coefficients are calculated for the FCC and BCC multicomponent concentrated alloys for simple sets of jump frequencies, including different stabilities of the different defects. A first approximation leads to an analytical expression of the Onsager coefficients in a binary alloy, and a second approximation provides a more accurate prediction. The results of the SCMF theory are compared with existing models and available Monte Carlo simulations, and an interpretation of the set of effective interactions in terms of a competition between jump frequencies is proposed.     

Distribution of spectral widths and preponderance of spin-0 ground states in nuclei

We use a single j-shell model with random two-body interactions to derive closed expressions for the distribution of and the correlations between spectral widths of different spins. This task is facilitated by introducing two-body operators whose squared spectral widths sum up to the squared spectral width of the random Hamiltonian. The spin-0 width is characterized by a relatively large average value and small fluctuations, while the width of maximum spin has the largest average and the largest fluctuations. The approximate proportionality between widths and spectral radii explains the preponderance of spin-0 ground states.     

Spin-spin cross relaxation in single-molecule magnets

The one-body tunnel picture of single-molecule magnets (SMMs) is not always sufficient to explain the measured tunnel transitions. An improvement to the picture is proposed by including also two-body tunnel transitions such as spin-spin cross relaxation (SSCR) which are mediated by dipolar and weak superexchange interactions between molecules. A Mn4 SMM is used as a model system. At certain external fields, SSCRs lead to additional quantum resonances which show up in hysteresis loop measurements as well-defined steps. A simple model is used to explain quantitatively all observed transitions.     

Adsorption configurations of carbon monoxide on gold monolayer supported by graphene or monolayer hexagonal boron nitride: a first-principles study

Using density functional theory with a semiempirical van der Waals approach proposed by Grimme, the adsorption behavior of carbon monoxide on a gold monolayer supported by graphene or monolayer hexagonal boron nitride has been investigated. Based on the changes in the Dirac cone of graphene and a Bader charge analysis, we observe that the Au(111) monolayer gains a small charge from graphene and monolayer h-BN. The adsorbed CO molecule adopts similar adsorption configurations on Au(111)/graphene and Au(111)/h-BN with Au-C distance 2.17?2.50 Å and Au-C-O angle of 123.9°–139.6°. Moreover, we found that for low CO coverages, bonding to the gold surface is surprisingly energy-favorable. Yet the CO adsorption binding energy diminishes at high coverage due to the repulsive van der Waals interactions between CO molecules.     

Phase diagram of the Kohn-Luttinger superconducting state for bilayer graphene

The effect of Coulomb interaction between Dirac fermions on the formation of the Kohn-Luttinger superconducting state in bilayer doped graphene is studied disregarding of the effect of the van der Waals potential of the substrate and impurities. The phase diagram determining the boundaries of superconductive domains with different types of symmetry of the order parameter is built using the extended Hubbard model in the Born weak-coupling approximation with allowance for the intratomic, interatomic, and interlayer Coulomb interactions between electrons. It is shown that the Kohn-Luttinger polarization contributions up to the second order of perturbation theory in the Coulomb interaction inclusively and an account for the long-range intraplane Coulomb interactions significantly affect the competition between the superconducting phases with the f-, p + ip-, and d + id-wave symmetries of the order parameter. It is demonstrated that the account for the interlayer Coulomb interaction enhances the critical temperature of the transition to the superconducting phase.     

Optical properties of thiol terminated biphenyloxazole ordered monolayers on gold surface

New thiol terminated biphenyloxazole molecules are synthesized. A self assembled monolayer has been prepared on gold surface and spectral and luminescent properties of free molecules and ordered films have been studied experimentally and theoretically (DFT). The luminescence polarization degree is about 40%. New absorption and luminescence bands have been found experimentally and confirmed theoretically. The highest occupied and the lowest unoccupied molecular orbitals of adsorbed molecules strongly differ from not adsorbed thiol molecules.     

Influence of the dipole-dipole interaction on velocity-selective coherent population trapping

We analyze the influence of the dipole-dipole interaction between ground and excited state atoms on atomic cooling by velocity-selective coherent population trapping. We consider two three-level atoms in the -configuration, interacting with two counterpropagating laser fields as well as with the electromagnetic vacuum modes. The elimination of these modes in the Born-Markov approximation results in spontaneous decay, which is essential in providing the momentum diffusion necessary for cooling, as well as a two-body dipole-dipole interaction between ground-and excited-state atoms. The corresponding two-body master equation is solved numerically by Monte-Carlo wave-function simulations. Our main result is that although a dark state survives the inclusion of dipole-dipole interactions, the presence of this interaction can significantly slow down the cooling process for sufficiently high atomic densities.Dedicated to H. Walther on the occasion of his 60th birthdayStrictly speaking, VSCPT is not a true cooling mechanism. The final atomic distribution cannot be characterized by a temperature, so that there is some ambiguity in characterizing the cooling efficiency. We return to this point in Sect. 3     

Analytic Atomic Screening Parameters for Slater Type Orbitals

Screening parameters to be used in Slater Type Orbitals were obtained in analytic form. The values compared well with the numerical results given by Clementi and Roetti (after a laborious process of optimization) and with the phenomenological values of Jung and Gould. The analytic formulation is based on the splitting of the two-body operator 1/r_st as the sum of effective one-body operators.     

重离子碰撞两体关联输运理论──Ⅰ．理论模型：相干态表象的构造与基本运动方程

应用相干态表象和两体关联动力学，建立了非相对论重离子碰撞两体关联输运理论ＴＢＣＴＴ（Ｔｗｏ—ＢｏｄｙＣｏｒｒｅｌａｔｉｏｎＴｒａｎｓｐｏｒｔＴｈｅｏｒｙ）．这一理论包括了时间相关的平均场．泡利阻塞和两体碰撞效应，它能够描述重离子碰撞过程中非均匀核物质的演化、涨落效应和碎裂的动力学形成．     

Polarization observables in (γ,NN) reactions

The formalism of ( γ, NN) reactions is given where the incident photon is polarized and the outgoing-nucleon polarization is detected. Sixteen structure functions and fifteen polarization observables are found in the general case, while only eight structure functions and seven polarization observables survive in coplanar kinematics. Numerical examples are presented for the ¹⁶O(γ, np) and ¹⁶O(γ, pp) reactions. The transitions to the ground state of ¹⁴C and ¹⁴N are calculated in a model where realistic short-range and tensor correlations are taken into account for the np pair, while short-range and long-range correlations are included in a consistent way for pp pairs. The effects of the one-body and two-body components of the nuclear current and the role of correlations in cross-sections and polarizations are studied and discussed. Received: 7 June 2001 / Accepted: 26 September 2001     

Two -Body Correlation Transport Theory for Heavy Ion Collisions Ⅰ. Theory Model: Construction of Coherent State Representation and Basic Equations of Motion

A two-body correlation transport theory(TBCTT) for describing the dynamical process in heavy ion collisions(HIC)is established by means of time-dependent coherent single particle state representations and the two-body correlation dynamics.Containing time-dependent mean field effect, Pauli block, and two-body collisions,this model is capable of describing the time-evolution of nonuniform nuclear matter,fluctuation effects and dynamical formation of fragments in HIC.     

Statistical properties of trading volume of Chinese stocks

The cumulative distribution of trading volume is investigated for Chinese stocks. Different from the power-law scaling of mature markets, the distribution is well fitted by a stretched exponential function . With the autocorrelation function and the detrended fluctuation analysis, the long-range autocorrelation of trading volume is revealed. The conditional dependence of volume on volatility and the volume-volatility cross-correlation are studied, and a positive long-range correlation between volume and volatility is observed.