arXiv subjects

W. Zwerger

Publications and source records attributed to W. Zwerger.

43 records · Page 3Linked to original sources

arXiv1999

Density matrix renormalization group for disordered bosons in one dimension

We calculate the zero-temperature phase diagram of the disordered Bose-Hubbard model in one dimension using the density matrix renormalization group. For integer filling the Mott insulator is always separated from the superfluid by a Bose glass phase. There is a reentrance of the Bose glass both as a function of the repulsive interaction and of disorder. At half-filling where no Mott insulator exists, the superfluid density has a maximum where the kinetic and repulsive energies are about the same. Superfluidity is suppressed both for small and very strong repulsion but is always monotonic in disorder.

cond-mat↗

arXiv1998

Comment on ``Jellium model of metallic nanocohesion''

In a recent letter Stafford, Baeriswyl and Burki have provided a simple model for the elastic force in metallic constrictions of nanometer size. By employing a semiclassical Weyl expansion for the density of states of transverse modes, we show that for any smooth cross section, there is a universal contribution (4 epsilon_F)/(9 lambda_F) to the average force which is absent in the presence of a hole.

cond-mat.mes-hall↗

arXiv1998

Low temperature thermodynamics of inverse square spin models in one dimension

We present a field-theoretic renormalization group calculation in two loop order for classical O(N)-models with an inverse square interaction in the vicinity of their lower critical dimensionality one. The magnetic susceptibility at low temperatures is shown to diverge like $T^{-a} \exp(b/T)$ with $a=(N-2)/(N-1)$ and $b=2π^2/(N-1)$. From a comparison with the exactly solvable Haldane-Shastry model we find that the same temperature dependence applies also to ferromagnetic quantum spin chains.

cond-mat.stat-mech↗

arXiv1997

Gauge Fields, Mode Mixing and Local Density of States in a Quantum Point Contact

It is shown that the elimination of the discrete transverse motion in a waveguide of arbitrary shape may be described in terms of a non-abelian gauge field for the longitudinal dynamics. This allows for an exact treatment of the scattering between different modes by eliminating the gauge field at the expense of a non-diagonal matrix of local subband energies. The method is applied to calculate the local density of states (LDOS) in a quantum point contact. Contrary to the total conductance which is well described by an adiabatic approximation, mode mixing turns out to play a crucial role for local properties like the LDOS.

cond-mat.mes-hall↗

arXiv1997

Ginzburg-Landau theory of superconductors with short coherence length

We consider Fermions in two dimensions with an attractive interaction in the singlet d-wave channel of arbitrary strength. By means of a Hubbard-Stratonovich transformation a statistical Ginzburg-Landau theory is derived, which describes the smooth crossover from a weak-coupling BCS superconductor to a condensate of composite Bosons. Adjusting the interaction strength to the observed slope of H_c2 at T_c in the optimally doped high-T_c compounds YBCO and BSCCO, we determine the associated values of the Ginzburg-Landau correlation length xi and the London penetration depth lambda. The resulting dimensionless ratio k_F xi(0) approx 5-8 and the Ginzburg-Landau parameter kappa=lambda xi approx 90-100 agree well with the experimentally observed values. These parameters indicate that the optimally doped materials are still on the weak coupling side of the crossover to a Bose regime.

cond-mat.supr-con↗

arXiv1997

Backflow in a Fermi Liquid

We calculate the backflow current around a fixed impurity in a Fermi liquid. The leading contribution at long distances is radial and proportional to 1/r^2. It is caused by the current induced density modulation first discussed by Landauer. The familiar 1/r^3 dipolar backflow obtained in linear response by Pines and Nozieres is only the next to leading term, whose strength is calculated here to all orders in the scattering. In the charged case the condition of perfect screening gives rise to a novel sum rule for the phase shifts. Similar to the behavior in a classical viscous liquid, the friction force is due only to the leading contribution in the backflow while the dipolar term does not contribute.

cond-mat.str-el↗

arXiv1996

The Single-Electron-Box and the Helicity Modulus of an inverse square XY-Model

We calculate the average number of electrons on a metallic single-electron-box as a function of the gate voltage for arbitrary values of the tunneling conductance. In the vicinity of the plateaus the problem is equivalent to calculating the helicity modulus of a classical inverse square XY-model in one dimension. By a combination of perturbation theory, a two-loop renormalization group calculation and a Monte-Carlo simulation in the intermediate regime we provide a complete description of the smearing of the Coulomb staircase at zero temperature with increasing conductance.

cond-mat.mes-hall↗