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 $\pm{\bf Q}$. 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: $\gamma_{QED} = \frac{e^2 T}{4\pi}(2.70)$. 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 ($V(r) \approx 1/r$) 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 $4k_F$ 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, $t_{\perp}$, 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, $U$, there exists a crossover value of the interladder one-particle hopping, $t_{\perp c}$. For $0<t_{\perp}<t_{\perp c}$, the spin gap metal (SGM) phase of the isolated ladder transits at a finite transition temperature, $T_{c}$, to the d-wave superconducting (SCd) phase via a two-particle crossover. In the temperature region, $T<T_{c}$, interladder coherent Josephson tunneling of the Cooper pairs occurs, while the interladder coherent one-particle process is strongly suppressed. For $t_{\perp c}<t_{\perp}$, around a crossover temperature, $T_{cross}$, the system crosses over to the two-dimensional (2D) phase via a one-particle crossover. In the temperature region, $T<T_{cross}$, 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 $\mathrm{Sr_{14-x}Ca_xCu_{24}O_{41}}$ reveal an approximately linear power law regime in the c-axis DC resistivity as a function of temperature for $x=11$. 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

Renormalization of impurity scattering in one-dimensional interacting electron systems in magnetic field

We study the renormalization of a single impurity potential in one-dimensional interacting electron systems in the presence of magnetic field. Using the bosonization technique and Bethe ansatz solutions, we determine the renormalization group flow diagram for the amplitudes of scattering of up- and down-spin electrons by the impurity in a quantum wire at low electron density and in the Hubbard model at less than half filling. In the absence of magnetic field the repulsive interactions are known to enhance backscattering and make the impurity potential impenetrable in the low-energy limit. On the contrary, we show that in a strong magnetic field the interaction may suppress the backscattering of majority-spin electrons by the impurity potential in the vicinity of the weak-potential fixed point. This implies that in a certain temperature range the impurity becomes almost transparent for the majority-spin electrons while it is impenetrable for the minority-spin ones. The impurity potential can thus have a strong spin-filtering effect.Comment: 11 pages, 2 figures; v2: a typo corrected and a reference added; v3: published version, Sec.II revised with an additional explanatory subsection, comments on the case of more than half-filling added, typos corrected, a reference update