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Comment: 4 pages, 3 figures, LaTex Wiley-VCH style (class files included), accepted for publication in proceedings of PASPS-IV
We have developed a fast, yet highly reproducible method to fabricate metallic electrodes with nanometer separation using electromigration (EM). We employ four-terminal instead of two-terminal devices in combination with an analog feedback to maintain the voltage $U$ over the junction constant. After the initialization phase ($U < 0.2V), during which the temperature $T$ increases by 80-150 degs C, EM sets in shrinking the wire locally. This quickly leads to a transition from the diffusive to a quasi-ballistic regime ($0.2V < U < 0.6V). At the end of this second regime, a gap forms (U > 0.6V). Remarkably, controlled electromigration is still possible in the quasi-ballistic regime.
Comment: 33 pages, 17 figures (Review article, 2008 conference of ultrafast electron microscopy conference and ultrafast sciences)
Analytical multi-domain solutions to the dynamical (Landau-Lifshitz-Gilbert) equation of a one-dimensional ferromagnet including an external magnetic field and spin-polarized electric current are found using the Hirota bilinearization method. A standard approach to solve the Landau-Lifshitz equation (without the Gilbert term) is modified in order to treat the dissipative dynamics. I establish the relations between the spin interaction parameters (the constants of exchange, anisotropy, dissipation, external-field intensity, and electric-current intensity) and the domain-wall parameters (width and velocity) and compare them to the results of the Walker approximation and micromagnetic simulations. The domain-wall motion driven by a longitudinal external field is analyzed with especial relevance to the field-induced collision of two doma...
We report the observation of a reentrant quantum Hall state at the Landau level filling factor nu = 1 in a two-dimensional hole system confined to a 35-nm-wide (001) GaAs quantum well. The reentrant behavior is characterized by a weakening and eventual collapse of the nu = 1 quantum Hall state in the presence of a parallel magnetic field component B||, followed by a strengthening and reemergence as B|| is further increased. The robustness of the nu = 1 quantum Hall state during the transition depends strongly on the charge distribution symmetry of the quantum well, while the magnitude of B|| needed to invoke the transition increases with the total density of the system.
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