19,665 research outputs found
Quantum fluctuations in the spiral phase of the Hubbard model
We study the magnetic excitations in the spiral phase of the two--dimensional
Hubbard model using a functional integral method. Spin waves are strongly
renormalized and a line of near--zeros is observed in the spectrum around the
spiral pitch . The possibility of disordered spiral states is
examined by studying the one--loop corrections to the spiral order parameter.
We also show that the spiral phase presents an intrinsic instability towards an
inhomogeneous state (phase separation, CDW, ...) at weak doping. Though phase
separation is suppressed by weak long--range Coulomb interactions, the CDW
instability only disappears for sufficiently strong Coulomb interaction.Comment: Figures are NOW appended via uuencoded postscript fil
The soft fermion dispersion relation at next-to-leading order in hot QED
We study next-to-leading order contributions to the soft static fermion
dispersion relation in hot QED. We derive an expression for the complete
next-to-leading order contribution to the retarded fermion self-energy. The
real and imaginary parts of this expression give the next-to-leading order
contributions to the mass and damping rate of the fermionic quasi-particle.
Many of the terms that are expected to contribute according to the traditional
power counting argument are actually subleading. We explain why the power
counting method over estimates the contribution from these terms. For the
electron damping rate in QED we obtain: . We check our method by calculating the next-to-leading order
contribution to the damping rate for the case of QCD with two flavours and
three coulours. Our result agrees with the result obtained previously in the
literature. The numerical evaluation of the nlo contribution to the mass is
left to a future publication.Comment: 15 pages, 5 figure
On the metal-insulator transition in the two-chain model of correlated fermions
The doping-induced metal-insulator transition in two-chain systems of
correlated fermions is studied using a solvable limit of the t-J model and the
fact that various strong- and weak-coupling limits of the two-chain model are
in the same phase, i.e. have the same low-energy properties. It is shown that
the Luttinger-liquid parameter K_\rho takes the universal value unity as the
insulating state (half-filling) is approached, implying dominant d-type
superconducting fluctuations, independently of the interaction strength. The
crossover to insulating behavior of correlations as the transition is
approached is discussed.Comment: 7 pages, 1 figur
Current reversal and exclusion processes with history-dependent random walks
A class of exclusion processes in which particles perform history-dependent
random walks is introduced, stimulated by dynamic phenomena in some biological
and artificial systems. The particles locally interact with the underlying
substrate by breaking and reforming lattice bonds. We determine the
steady-state current on a ring, and find current-reversal as a function of
particle density. This phenomenon is attributed to the non-local interaction
between the walkers through their trails, which originates from strong
correlations between the dynamics of the particles and the lattice. We
rationalize our findings within an effective description in terms of
quasi-particles which we call front barriers. Our analytical results are
complemented by stochastic simulations.Comment: 5 pages, 6 figure
Wigner Crystal in One Dimension
A one--dimensional gas of electrons interacting with long--range Coulomb
forces () is investigated. The excitation spectrum consists
of separate collective charge and spin modes, with the charge excitation
energies in agreement with RPA calculations. For arbitrarily weak Coulomb
repulsion density correlations at wavevector decay extremely slowly and
are best described as those of a one--dimensional Wigner crystal. Pinning of
the Wigner crystal then leads to the nonlinear transport properties
characteristic of CDW. The results allow a consistent interpretation of the
plasmon and spin excitations observed in one--dimensional semiconductor
structures, and suggest an interpretation of some of the observed features in
terms of ``spinons''. A possible explanation for nonlinear transport phenomena
is given.Comment: 10 pages, RevTe
Spin Gap and Superconductivity in Weakly Coupled Ladders: Interladder One-particle vs. Two-particle Crossover
Effects of the interladder one-particle hopping, , on the
low-energy asymptotics of a weakly coupled Hubbard ladder system have been
studied, based on the perturbative renormalization-group approach. We found
that for finite intraladder Hubbard repulsion, , there exists a crossover
value of the interladder one-particle hopping, . For
, the spin gap metal (SGM) phase of the isolated
ladder transits at a finite transition temperature, , to the d-wave
superconducting (SCd) phase via a two-particle crossover. In the temperature
region, , interladder coherent Josephson tunneling of the Cooper pairs
occurs, while the interladder coherent one-particle process is strongly
suppressed. For , around a crossover temperature,
, the system crosses over to the two-dimensional (2D) phase via a
one-particle crossover. In the temperature region, , the
interladdercoherent band motion occurs.Comment: 4 pages, 5 eps figures, uses jpsj.st
Open t-J chain with boundary impurities
We study integrable boundary conditions for the supersymmetric t-J model of
correlated electrons which arise when combining static scattering potentials
with dynamical impurities carrying an internal degree of freedom. The latter
differ from the bulk sites by allowing for double occupation of the local
orbitals. The spectrum of the resulting Hamiltonians is obtained by means of
the algebraic Bethe Ansatz.Comment: LaTeX2e, 9p
Role of Umklapp Processes in Conductivity of Doped Two-Leg Ladders
Recent conductivity measurements performed on the hole-doped two-leg ladder
material reveal an approximately linear
power law regime in the c-axis DC resistivity as a function of temperature for
. In this work, we employ a bosonic model to argue that umklapp processes
are responsible for this feature and for the high spectral weight in the
optical conductivity which occurs beyond the finite frequency Drude-like peak.
Including quenched disorder in our model allows us to reproduce experimental
conductivity and resistivity curves over a wide range of energies. We also
point out the differences between the effect of umklapp processes in a single
chain and in the two-leg ladder.Comment: 10 pages, 2 figure
Concentration fields near air-water interfaces during interfacial mass transport: oxygen transport and random square wave analysis
Mass transfer across a gas-liquid interface was studied theoretically and experimentally, using transfer of oxygen into water as the gas-liquid system. The experimental results support the conclusions of a theoretical description of the concentration field that uses random square waves approximations. The effect of diffusion over the concentration records was quantified. It is shown that the peak of the normalized rms concentration fluctuation profiles must be lower than 0.5, and that the position of the peak of the rms value is an adequate measure of the thickness of the diffusive layer. The position of the peak is the boundary between the regions more subject to molecular diffusion or to turbulent transport of dissolved mass
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