The role of domain walls on the vortex creep dynamics in unconventional superconducors

We investigate the influence of domain walls on the vortex dynamics in superconductors with multi-component order parameters. We show that, due to their complex structure domain walls can carry vortices with fractional flux quanta. The decay of conventional vortices into fractional ones on domain walls is examined. This decay presents an extraordinarily strong pinning mechanism for vortices and turns domain walls occupied with pinned fractional vortices into efficient barriers for the vortex motion. Therefore, domain walls can act as fences for the flux flow, preventing the decay of the remnant magnetic flux enclosed by them. Furthermore, the consequences of this property of domain walls on the vortex dynamics are discussed in connection with observed noise in the hysteresis cycle, using the Bean model of the critical vortex state. Based on this picture experimental data in the unconventional superconductors UPt$_3$, U$_{1-x}$Th$_x$Be$_{13}$ and Sr$_2$RuO$_4$ are interpreted.Comment: 18 pages, 9 figures, to appear in Progress of Theoretical Physic

What if? Policy analysis with calibrated equilibrium models

The goal of this paper is to build up and apply a simple static model of world oil markets.CGE, static model, oil markets

Checkerboard order in the t--J model on the square lattice

We propose that the inhomogeneous patterns seen by STM in some underdoped superconducting cuprates could be related to a bond-order-wave instability of the staggered flux state, one of the most studied "normal" state proposed to compete with the d-wave RVB superconductor. A checkerboard pattern is obtained by a Gutzwiller renormalized mean-field theory of the t-J model for doping around 1/8. It is found that the charge modulation is always an order of magnitude smaller than the bond-order modulations. This is confirmed by an exact optimization of the wavefunction by a variational Monte Carlo scheme. The numerical estimates of the order parameters are however found to be strongly reduced w.r.t their mean-field values

Spin, charge and orbital fluctuations in a multi-orbital Mott insulator

The two-orbital degenerate Hubbard model with distinct hopping integrals is studied by combining dynamical mean-field theory with quantum Monte Carlo simulations. The role of orbital fluctuations for the nature of the Mott transition is elucidated by examining the temperature dependence of spin, charge and orbital susceptibilities as well as the one-particle spectral function. We also consider the effect of the hybridization between the two orbitals, which is important particularly close to the Mott transition points. The introduction of the hybridization induces orbital fluctuations, resulting in the formation of a Kondo-like heavy-fermion behavior, similarly to $f$ electron systems, but involving electrons in bands of comparable width.Comment: 8 pages, 9 figure

Bond order wave instabilities in doped frustrated antiferromagnets: "Valence bond solids" at fractional filling

We explore both analytically and numerically the properties of doped t-J models on a class of highly frustrated lattices, such as the kagome and the pyrochlore lattice. Focussing on a particular sign of the hopping integral and antiferromagnetic exchange, we find a generic symmetry breaking instability towards a twofold degenerate ground state at a fractional filling below half filling. These states show modulated bond strengths and only break lattice symmetries. They can be seen as a generalization of the well-known valence bond solid states to fractional filling.Comment: slightly shortened and reorganized versio

Extreme vortex pinning in the non-centrosymmetric superconductor CePt3_{3}Si

We report on the vortex dynamics of a single crystal of the non-centrosymmetric heavy-fermion superconductor CePt$_{3}$Si. Decays of the remnant magnetization display a clean logarithmic time dependence with rates that follow the temperature dependence expected from the Kim-Anderson theory. The creep rates are lower than observed in any other centrosymmetric superconductor and are not caused by high critical currents. On the contrary, the critical current in CePt$_{3}$Si is considerably lower than in other superconductors with strong vortex pinning indicating that an alternative impediment on the flux line motion might be at work in this superconductor.Comment: 4 pages, 5 figure

Vortex pinning and stability in the low field, superconducting phases of UPt_3

We use an array of miniature Hall probe magnetometers to probe the entry and flow of flux in a single crystal torus or the heavy fermion superconductor UPt_3. Local measurements over the hole are exquisitely sensitive to vortex motion anywhere in the torus, and they permit us to detect avalanches restricted to and with a sharp onset in the lower temperature superconducting phase. Computer simulations support a mechanism dependent upon the degenerate nature of the superconducting order parameter

One-dimensional Kondo lattice at partial band filling

An effective Hamiltonian for the localized spins in the one-dimensional Kondo lattice model is derived via a unitary transformation involving a bosonization of delocalized conduction electrons. The effective Hamiltonian is shown to reproduce all the features of the model as identified in various numerical simulations, and provides much new information on the ferro- to paramagnetic phase transition and the paramagnetic phase.Comment: 11 pages Revtex, 1 Postscript figure. To appear in Phys. Rev. Let