arXiv subjects
Publications and source records attributed to P. Woelfle.
The interaction of a surface acoustic wave (SAW) with a a two-dimensional electron gas in a periodic electric potential and a classical magnetic field is considered. We calculate the attenuation of the SAW and its velocity change and show that these quantities exhibit Weiss oscillations.
We study transport in a smooth random magnetic field, with emphasis on composite fermions (CF) near half-filling of the Landau level. When either the amplitude of the magnetic field fluctuations or its mean value $\bar B$ is large enough, the transport is of percolating nature. While at $\bar{B}=0$ the percolation effects enhance the conductivity $σ_{xx}$, increasing $\bar B$ (which corresponds to moving away from half-filling for the CF problem) leads to a sharp falloff of $σ_{xx}$ and, consequently, to the quantum localization of CFs. We demonstrate that the localization is a crucial factor in the interplay between the Shubnikov-de Haas and quantum Hall oscillations, and point out that the latter are dominant in the CF metal.
We study the dimensional crossover of weak localization in strongly anisotropic systems. This crossover from three-dimensional behavior to an effective lower dimensional system is triggered by increasing temperature if the phase coherence length gets shorter than the lattice spacing $a$. A similar effect occurs in a magnetic field if the magnetic length $L_m$ becomes shorter than $a(D_{||}/D_\perp)^γ$, where $\D_{||}/D_\perp$ is the ratio of the diffusion coefficients parallel and perpendicular to the planes or chains. $γ$ depends on the direction of the magnetic field, e.g. $γ=1/4$ or 1/2 for a magnetic field parallel or perpendicular to the planes in a quasi two-dimensional system. We show that even in the limit of large magnetic field, weak localization is not fully suppressed in a lattice system. Experimental implications are discussed in detail.
We consider the conductivity tensor for composite fermions in a close to half-filled Landau band in the temperature regime where the scattering off the potential and the trapped gauge field of random impurities dominates. The Boltzmann equation approach is employed to calculate the quasiclassical transport properties at finite effective magnetic field, wavevector and frequency. We present an exact solution of the kinetic equation for all parameter regimes. Our results allow a consistent description of recently observed surface acoustic wave resonances and other findings.
We calculate the Altshuler-Aronov type quantum correction to the conductivity of $2d$ charge carriers in a random potential (or random magnetic field) coupled to a transverse gauge field. The gauge fields considered simulate the effect of the Coulomb interaction for the fractional quantum Hall state at half filling and for the $t-J$ model of high-$T_c$ superconducting compounds. We find an unusually large quantum correction varying linearly or quadratically with the logarithm of temperature, in different temperature regimes.
We develop a quasiclassical method based on the path integral formalism, to study the influence of disorder on magnetooscillations of the density of states and conductivity. The treatment is appropriate for electron systems in the presence of a random potential with large correlation length or a random magnetic field, which are characterisitic features of various 2D electronic systems presently studied in experiment. In particular, we study the system of composite fermions in the fractional quantum Hall effect device, which are coupled to the Chern--Simons field and subject to a long--range random potential.
We present a theory of magnetooscillations around the $ν=1/2$ Landau level filling factor based on a model with a fluctuating Chern--Simons field. The quasiclassical treatment of the problem is appropriate and leads to an unconventional $\exp\left[-(π/ω_cτ^*_{1/2})^4\right]$ behavior of the amplitude of oscillations. This result is in good qualitative agreement with available experimental data.
We use the numerical renormalization group to calculate the auxiliary spectral functions of the $U=\infty$ Anderson impurity model. The slave--boson and pseudo--fermion spectral functions diverge at the threshold with exponents $α_{b}$ and $α_{f}$ given in terms of the conduction electron phase shifts by the X--ray photoemission and the X--ray absorption exponents respectively. The exact exponents obtained here depend on the impurity occupation number, in contrast to the NCA results. Vertex corrections in the convolution formulae for physical Green's functions are singular at the threshold and may not be neglected in the Fermi liquid regime.
We consider the single particle relaxation rate of 2D electrons subject to a random magnetic field. The density of states (DOS) oscillations in a uniform magnetic field (in addition to a random one) are studied. We define a gauge invariant single particle relaxation time as a parameter describing the amplitude of DOS oscillations. Unlike the conventional case of random potential scattering the broadening of the Landau levels does not depend on magnetic field.
We consider a charged quantum particle in a random magnetic field with Gaussian, delta-correlated statistics. We show that although the single particle properties are peculiar, two particle quantities such as the diffusion constant can be calculated in perturbation theory. We map the problem onto a non-linear sigma-model for Q-matrices of unitary symmetry with renormalized diffusion coefficient for which all states are known to be localized in $d=2$ dimensions. Our results compare well with recent numerical data.