Coulomb drag between one-dimensional conductors

We have analyzed Coulomb drag between currents of interacting electrons in two parallel one-dimensional conductors of finite length L attached to external reservoirs. For strong coupling, the relative fluctuations of electron density in the conductors acquire energy gap M. At energies larger than gamma = constxv(-)exp(-LM/v(-))/L+gamma(+), where gamma(+) is the impurity scattering rate, and, for L>v(-)/M, where v(-) is the fluctuation velocity, the gap leads to an "ideal" drag with almost equal currents in the conductors. At low energies the drag is suppressed by coherent instanton tunneling, and the zero-temperature transconductance vanishes, indicating the Fermi-liquid behavior.     

Local field correction effect on inelastic Coulomb scattering lifetime of two-dimensional quasiparticles at low temperatures

We have investigated the effect of local field correction on the inelastic Coulomb scattering lifetime of high mobility quasiparticles in a quantum layer at low temperatures. By replacing temperature-dependent dynamic dielectric function for the zero-temperature one in calculations, we have considered our improved zero-temperature STLS local field correction for low temperatures in lifetime calculations and compared the results with those obtained from the RPA and Hubbard approximation. It has been found that the quasiparticle lifetime decreases by including the STLS local field factor in all temperatures, energies and layer thicknesses.     

Double-resonant structure in the high-frequency transresistance of coupled electron-hole systems

The linear dc and high-frequency transresistivity of coupled electron-hole systems are investigated using the Lei-Ting balance equations approach extended to include many-body corrections. A possible indirect method of experimentally measuring the dynamical transresistivity in the high frequency (terahertz) regime is designed basing on the detailed analysis on the relationship between the directly measurable resistivities in the electron- and hole-layer and the dynamical transresistance. The theoretically predicted dc transresistance is in good agreement with the experimental data for the given electron-hole system experimentally investigated. The calculated dynamical transresistance exhibits pronounced double-resonant structure, which can be attributed to the cooperation and competition between the two plasmon modes. It is pointed out that the behavior of the frequency-dependent transresistance is temperature-sensitive and the dynamical transport properties are essentially influenced by the short range correlations. Received: 1st April 1998 / Revised: 22 June 1998 / Accepted: 6 August 1998     

Jamming as a critical phenomenon: a field theory of zero-temperature grain packings

A field theory of frictionless grain packings in two dimensions is shown to exhibit a zero-temperature critical point at a nonzero value of the packing fraction. The zero-temperature constraint of force balance plays a crucial role in determining the nature of the transition. Two order parameters, , the deviation of the average number of contacts from the isostatic value, and , the average magnitude of the force per contact, characterize the transition from the jammed (high packing fraction) to the unjammed (low packing fraction state). The critical point has a mixed character with the order parameters showing a jump discontinuity but with fluctuations of the contact force diverging. At the critical point, the distribution of phi shows the characteristic plateau observed in static granular piles. The theory makes falsifiable predictions about the spatial fluctuations of the contact forces.     

Phonon focusing and electron–phonon drag in semiconductor crystals with degenerate charge-carrier statistics

We study the effect of anisotropy in elastic properties on the electron–phonon drag and thermoelectric phenomena in gapless semiconductors with degenerate charge-carrier statistics. It is shown that phonon focusing leads to a number of new effects in the drag thermopower at low temperatures, when diffusive phonon scattering from the boundaries is the predominant relaxation mechanism. We analyze the effect of phonon focusing on the dependences of the thermoelectromotive force (thermopower) in HgSe:Fe crystals on geometric parameters and the heat-flow directions relative to the crystal axes in the Knudsen regime of the phonon gas flow. The crystallographic directions that ensure the maximum and minimum values of the thermopower are determined and the role of quasi-longitudinal and quasi-transverse phonons in the drag thermopower in HgSe:Fe crystals at low temperatures is analyzed. It is shown that the main contribution to the drag thermopower comes from slow quasi-transverse phonons in the directions of focusing in long samples.     

Random-bond Ising chain in a transverse magnetic field: A finite-size scaling analysis

We investigate the zero-temperature quantum phase transition of the randombond Ising chain in a transverse magnetic field. Its critical properties are identical to those of the McCoy-Wu model, which is a classical Ising model in two dimensions with layered disorder. The latter is studied via Monte Carlo simulations and transfer matrix calculations and the critical exponents are determined with a finite-size scaling analysis. The magnetization and susceptibility obey conventional rather than activated scaling. We observe that the order parameter and correlation function probability distribution show a nontrivial scaling near the critical point, which implies a hierarchy of critical exponents associated with the critical behavior of the generalized correlation lengths.     

Atomistic simulation of the motion of dislocations in metals under phonon drag conditions

The mobility of dislocations in the over-barrier motion in different metals (Al, Cu, Fe, Mo) has been investigated using the molecular dynamics method. The phonon drag coefficients have been calculated as a function of the pressure and temperature. The results obtained are in good agreement with the experimental data and theoretical estimates. For face-centered cubic metals, the main mechanism of dislocation drag is the phonon scattering. For body-centered cubic metals, the contribution of the radiation friction becomes significant at room temperature. It has been found that there is a correlation between the temperature dependences of the phonon drag coefficient and the lattice constant. The dependences of the phonon drag coefficient on the pressure have been calculated. In contrast to the other metals, iron is characterized by a sharp increase in the phonon drag coefficient with an increase in the pressure at low temperatures due to the α-∈ phase transition.     

Two-dimensional isotropic orientational glasses: a computer-simulation study

The analogue of the Edwards-Anderson model for isotropic vector spin glasses, but taking three-component quadrupoles instead of spins at each lattice site, is studied on the square lattice with extensive Monte Carlo calculations, using a nearest-neighbor symmetric gaussian interaction.It is shown that at low temperaturesT the model develops a short range order both with respect to glass like correlations and with respect to ferromagnetic correlations among the quadrupoles. The associated correlation lengths and susceptibilities diverge asT0, and the critical exponents for this zero-temperature phase transition are estimated.Dynamic correlation functions are analyzed as well and it is shown that the dacay of spatially displaced correlations displays a Kohlrausch-Williams-Watts behavior similar to the self-correlation function of the quadrupole moments.Some quantities are compared to their corresponding counterparts on the threedimensional simple cubic lattice, which also has a zero-temperature transition but at corresponding temperatures has stronger short-range-order.     

Co-Segregation Effects on Boundary Migration

We analyze the effect of co-segregation on the mobility of grain boundaries within the framework of the impurity drag theory originally proposed by Cahn and Lücke and Stüwe for an ideal solution. The new derivation extends this model to the case where there are two types of impurities (or three components in the alloy). Since the resultant expression for the boundary mobility is complicated, numerical solutions were obtained for several cases to show how co-segregation affects the boundary mobility. Depending on the relative diffusivities of the two impurities which are both attracted to the boundary, the mobility may either increase or decrease with increasing concentration of one of the impurities. When one of the impurities is attracted to the boundary and the other repelled from the boundary, increasing the concentration of the attractive impurity can lead to a sharp decrease in the boundary mobility.     

Derivation of the effective action of a dilute Fermi gas in the unitary limit of the BCS–BEC crossover

The effective action describing the gapless Nambu–Goldstone, or Anderson–Bogoliubov, mode of a zero-temperature dilute Fermi gas at unitarity is derived up to next-to-leading order in derivatives from the microscopic theory. Apart from a next-to-leading order term that is suppressed in the BCS limit, the effective action obtained in the strong-coupling unitary limit is proportional to that obtained in the weak-coupling BCS limit.     

Phase transition in a two-dimensional Ising ferromagnet based on the generalized zero-temperature Glauber dynamics

At zero temperature, based on the Ising model, the phase transition in a two-dimensional square lattice is studied using the generalized zero-temperature Glauber dynamics. Using Monte Carlo （MC） renormalization group methods, the static critical exponents and the dynamic exponent are studied; the type of phase transition is found to be of the first order.     

Multicritical point in a diluted bilayer Heisenberg quantum antiferromagnet

The S=1/2 Heisenberg bilayer antiferromagnet with randomly removed interlayer dimers is studied using quantum Monte Carlo simulations. A zero-temperature multicritical point (p(*),g(*)) at the classical percolation density p=p(*) and interlayer coupling g(*) approximately equal 0.16 is demonstrated. The quantum critical exponents of the percolating cluster are determined using finite-size scaling. It is argued that the associated finite-temperature quantum critical regime extends to zero interlayer coupling and could be relevant for antiferromagnetic cuprates doped with nonmagnetic impurities.     

Multiferroic phase transitions in manganites RMnO₃:A two-orbital double exchange simulation

The semi-quantum two-orbital exchange model is used to investigate the effect of small rare-earth ion substitution on orthorhombic RMnO 3 with A-type antiferromagnetic order,using the Monte Carlo algorithm,exact diagonalization,and zero-temperature optimization approaches.It is revealed that the substitution results in a rich multiferroic phase diagram where the coexisting A-type antiferromagnetic phase and spiral spin phase,pure spiral spin phase,coexisting spiral spin phase,the E-type antiferromagnetic phase,and the pure E-type antiferromagnetic phase emerge in sequence.The multiferroic phase transitions modulate substantially the electric polarization,which is consistent qualitatively with recent experiments.     

Confinement-deconfinement interplay in quantum phases of doped Mott insulators

In the t-J model, the electron fractionalization is dictated by the phase string effect. We find that in the underdoped regime, the antiferromagnetic and superconducting phases are dual: in the former, holons are confined while spinons are deconfined, and vice?versa in the latter. These two phases are separated by a novel phase, the so-called Bose-insulating phase, where both holons and spinons are deconfined. A pair of Wilson loops was found to constitute a complete set of order parameters determining this zero-temperature phase diagram. The quantum phase transitions between these phases are suggested to be of non-Landau-Ginzburg-Wilson type.     

Quantum superconductor-metal transition in a proximity array

A theory of the zero-temperature superconductor-metal transition is developed for an array of superconductive islands (of size d) coupled via a disordered two-dimensional conductor with the dimensionless conductance g = Planck's over 2 pi/e(2)R(square)>1. At T = 0 the macroscopically superconductive state of the array with lattice spacing b>d is destroyed at g相似文献   

Space dependence of the order parameter in clean type II superconductors at low temperatures

An expression for the order parameter at large distances from the axis of vortex is presented. At zero-temperature and for infinite mean free path of the electrons the correction to the order parameter is different from zero.     

Lattice models for liquid crystals

A problem in the theory of liquid crystals is to construct a model system which at low temperatures displays long-range orientational order, but not translational order in all directions. We present five lattice models (two two-dimensional and three three-dimensional) of hard-core particles with attractive interactions and prove (using reflection positivity and the Peierls argument) that they have orientational order at low temperatures; the two-dimensional models have no such ordering if the attractive interaction is not present. We cannot prove that these models do not have complete translational order, but their zero-temperature states are such that we are led to conjecture that complete translational order is always absent.Work of EHL supported by U.S. National Science Foundation Grant MCS 75-21684 A02. Financial assistance from the Danish Natural Science Research Council is also gratefully acknowledged.     

Effect of the gas flow geometry and turbulence on the hydrodynamic drag of a body in the flow

The effect of the incoming flow geometry on the hydrodynamic drag of a body is investigated in a numerical experiment simulating a free gas flow past a sphere as well as flows in cylindrical tubes of various radii, in a confuser, and a diffuser. The results of calculations lead to the conclusion that the confinement of the flow by the tube walls, its contraction and expansion may change the hydrodynamic force and the drag acting on the body insignificantly (not more than by 30%). This cannot explain the early drag crisis, in which the values of these quantities decrease by 4–7 times for Reynolds numbers on the order of 100. This phenomenon is explained theoretically by the effect of strong turbulence of the incoming flow to the body.     

Statistical description of the shape of a moving dislocation

The shape and mobility of dislocations gliding (climbing) over the crystal relief are studied. The mobility of a dislocation is governed by the probability of critical nucleation on it of various defects (the formation of a double kink or break-away from a barrier during sliding, the formation of a jog during absorption (emission) of an interstitial (vacancy) during climbing, etc.). It is demonstrated that the transitional and steady-state modes of dislocation motion exist (the transitional and steady-state modes of deformation). The time required to achieve the steady-state dislocation motion and the velocity of this motion in the absence and in the presence of various types of pinning (drag) centers are calculated. The pinning centers qualitatively change the steady-state velocity of dislocations and increase the time required to reach this mode of motion.     

Rotational drag on DNA: a single molecule experiment

Within a single-molecule configuration, we have studied rotational drag on double stranded linear DNA by measuring the force during mechanical opening and closing of the double helix at different rates. The molecule is cranked at one end by the effect of unzipping and is free to rotate at the other end. In this configuration the rotational friction torque tau on double-stranded DNA leads to an additional contribution to the opening force. It is shown that the effect of rotational drag increases with the length of the molecule, is approximately proportional to the angular velocity of cranking, and we estimate that the torque tau is of the order of 1k(B)T for 10 000 base pairs of DNA cranked at 2000 turns per second.