A vortex crossing a thin-film superconducting strip from one edge to the other, perpendicular to the bias current, is the dominant mechanism of dissipation for films of thickness d on the order of the coherence length ξ and of width w much narrower than the Pearl length Λ ≫ w ≫ ξ. At high bias currents, I * < I < Ic, the heat released by the crossing of a single vortex suffices to create a belt-like normal-state region across the strip, resulting in a detectable voltage pulse. Here Ic is the critical current at which the energy barrier vanishes for a single vortex crossing. The belt forms along the vortex path and causes a transition of the entire strip into the normal state. We estimate I * to be roughly Ic/3. Further, we argue that such "hot" vortex crossings are the origin of dark counts in photon detectors, which operate in the regime of metastable superconductivity at currents between I * and Ic. We estimate the rate of vortex crossings and compare it with recent experimental data for dark counts. For currents below I * , i.e., in the stable superconducting but resistive regime, we estimate the amplitude and duration of voltage pulses induced by a single vortex crossing.

We present a unified description of the resonance peak and low-energy incommensurate response observed in high-Tc cuprate superconductors. We argue that both features have a purely magnetic origin and they represent universal features of an incommensurate spin state both below and above the superconducting transition temperature. In this description the resonance peak is the reflection of commensurate antiferromagnetism. Our theoretical scenario gives an account of the main features observed in various families of superconductors and predicts those not yet observed, like a resonance peak in La2NiO4+x.Neutron scattering experiments in the cuprates reveal two interesting and seemingly unrelated effects: (a) the low-energy incommensurate peaks at momenta k = These experimental observations are widely believed to be important for our understanding of the nature of the magnetic correlations and ultimately for the understanding of the superconductivity in high-T c materials.On the one hand the intensity and the energy E r of the resonance peak seems to scale with the superconducting coherence energy scale [3]This experimental observation was in fact used in Refs.[4] to relate the formation of the superconducting coherence to the opening of a new spin-scattering channel in the superconducting state that is impossible in the normal state above the superconducting critical temperature T c . Several theoretical scenarios attributed the origin of the resonance peak to superconducting coherence effects [5] or considered it as the fingerprint of a collective mode in an SO(5) symmetric field theory [6]. On the other hand the direct proportionality between δ and T c has been observed in recent neutron scattering data for LSCO and YBCO compounds [7] with some characteristic and material dependent velocity v * ∼ 17-35 meVÅ, where δ is measured in units of π a . One could argue that there is no immediate connection between the two phenomena [8]. In this case any relationship to superconductivity is accidental and hence there is no unifying physics to be learned from comparing these two sets of observations. Alternatively one can attempt to prove that these two phenomena are intimately related. This is the point of view we will advocate in this article: We argue for the common origin of both the low energy incommensurate response and resonance peak as a magnetic scattering in the disordered incommensurate spin state. In our interpretation the resonance peak is the spectral weight at energy E r associated to the lowest energy spinon excitation with k = Q in a system with spin incommensuration. A key aspect of our analysis is the realization that the experimental observations are different manifestations of a unique physical phenomenon.It is apparent that charge doping induces a certain spin ordering in these low-dimensional, doped, antiferromagnets [11] as a result of competing interactions. Indeed, in one spatial dimension this can be exactly shown to be the case [9]. Here, we will only consider the spin degrees of freedom and ...

The quantum phase diagram of the Hubbard chain with correlated hopping is accurately determined through jumps in π in the charge and spin Berry phases. The nature of each thermodynamic phase, and the existence of charge and spin gaps, is confirmed by calculating correlation functions and other fundamental quantities using numerical methods, and symmetry arguments. Remarkably we find striking similarities between the stable phases for moderate on-site Coulomb repulsion: spin Peierls, spin-density-wave and triplet superconductor, and those measured in (TMTSF)2X.