arXiv subjects

Uwe Claus Täuber

Publications and source records attributed to Uwe Claus Täuber.

4 recordsLinked to original sources

arXiv1996

Weakly Pinned Bose Glass vs. Mott Insulator Phase in Superconductors

We study the properties of the Bose glass phase of localized flux lines in irradiated superconductors near the matching field $B_Φ$. Repulsive vortex interactions destroy the Mott insulator phase predicted to occur at $B=B_Φ$. For ratios of the penetration depth to average defect distance $λ/ d \leq 1$ remnants of the Mott insulator singularities remain visible in the magnetization, the bulk modulus, and the magnetization relaxation, as B is varied near $B_Φ$. For $λ\geq d$, the ensuing weakly pinned Bose glass is characterized by a soft Coulomb gap in the distribution of pinning energies.

cond-mat.supr-con↗

arXiv1996

Mode coupling and renormalization group results for the noisy Burgers equation

We investigate the noisy Burgers equation (Kardar--Parisi--Zhang equation in 1+1 dimensions) using the dynamical renormalization group (to two--loop order) and mode--coupling techniques. The roughness and dynamic exponent are fixed by Galilean invariance and a fluctuation--dissipation theorem. The fact that there are no singular two--loop contributions to the two--point vertex functions supports the mode--coupling approach, which can be understood as a self--consistent one--loop theory where vertex corrections are neglected. Therefore, the numerical solution of the mode coupling equations yields very accurate results for the scaling functions. In addition, finite--size effects can be studied. Furthermore, the results from exact Ward identities, as well as from second--order perturbation theory permit the quantitative evaluation of the vertex corrections, and thus provide a quantitative test for the mode--coupling approach. It is found that the vertex corrections themselves are of the order one. Surprisingly, however, their effect on the correlation function is substantially smaller.

cond-mat↗

arXiv1994

Two-Loop Renormalization Group Analysis of the Burgers-Kardar-Parisi-Zhang Equation

A systematic analysis of the Burgers--Kardar--Parisi--Zhang equation in $d+1$ dimensions by dynamic renormalization group theory is described. The fixed points and exponents are calculated to two--loop order. We use the dimensional regularization scheme, carefully keeping the full $d$ dependence originating from the angular parts of the loop integrals. For dimensions less than $d_c=2$ we find a strong--coupling fixed point, which diverges at $d=2$, indicating that there is non--perturbative strong--coupling behavior for all $d \geq 2$. At $d=1$ our method yields the identical fixed point as in the one--loop approximation, and the two--loop contributions to the scaling functions are non--singular. For $d>2$ dimensions, there is no finite strong--coupling fixed point. In the framework of a $2+ε$ expansion, we find the dynamic exponent corresponding to the unstable fixed point, which describes the non--equilibrium roughening transition, to be $z = 2 + {\cal O} (ε^3)$, in agreement with a recent scaling argument by Doty and Kosterlitz. Similarly, our result for the correlation length exponent at the transition is $1/ν= ε+ {\cal O} (ε^3)$. For the smooth phase, some aspects of the crossover from Gaussian to critical behavior are discussed.

cond-mat↗

arXiv1994

Crossover from Self--Similar to Self--Affine Structures in Percolation

We study the crossover from self--similar scaling behavior to asymptotically self--affine (anisotropic) structures. As an example, we consider bond percolation with one preferred direction. Our theory is based on a field--theoretical representation, and takes advantage of a renormalization group approach designed for crossover phenomena. We calculate effective exponents for the connectivity describing the entire crossover region from isotropic to directed percolation, and predict at which scale of the anisotropy the crossover should occur. We emphasize the broad range of applicability of our method.

cond-mat↗