Modulated Rashba interaction in a quantum wire: Spin and charge dynamics

It was recently shown that a spatially modulated Rashba spin-orbit coupling in a quantum wire drives a transition from a metallic to an insulating state when the wave number of the modulation becomes commensurate with the Fermi wave length of the electrons in the wire. It was suggested that the effect may be put to practical use in a future spin transistor design. In the present article we revisit the problem and present a detailed analysis of the underlying physics. First, we explore how the build-up of charge density wave correlations in the quantum wire due to the periodic gate configuration that produces the Rashba modulation influences the transition to the insulating state. The interplay between the modulations of the charge density and that of the spin-orbit coupling turns out to be quite subtle: Depending on the relative phase between the two modulations, the joint action of the Rashba interaction and charge density wave correlations may either enhance or reduce the Rashba current blockade effect. Secondly, we inquire about the role of the Dresselhaus spin-orbit coupling that is generically present in a quantum wire embedded in semiconductor heterostructure. While the Dresselhaus coupling is found to work against the current blockade of the insulating state, the effect is small in most materials. Using an effective field theory approach, we also carry out an analysis of effects from electron- electron interactions, and show how the single-particle gap in the insulating state can be extracted from the more easily accessible collective charge and spin excitation thresholds. The smallness of the single-particle gap together with the anti-phase relation between the Rashba and chemical potential modulations pose serious difficulties for realizing a Rashba-controlled current switch in an InAs-based device. Some alternative designs are discussed.Comment: 20 pages, 6 figure

Coarsening and dendritic instability of spheroidal graphite in high silicon cast iron under thermal cycling in the ferritic domain

High silicon ferritic spheroidal graphite cast irons have been developed for high temperature service, in particular under thermal cycling conditions. The theoretical maximum service temperature is defined as the upper limit of the two-phase ferrite+graphite domain, which increases with the alloy silicon content. While isothermal heat treatment close to this temperature showed little evolution of the graphite distribution, thermal cycling led to a significant coarsening of the graphite particles associated with dendritic overgrowth of the large graphite particles. This unexpected behaviour is here observed and described for the first time

Spheroidal graphite coalescence during thermal cycling in the ferritic domain of a high-silicon cast iron studied by optical microscopy and X-ray computed tomography

High-silicon cast irons remain ferritic at higher temperature than usual cast irons and present both better oxidation resistance and higher mechanical strength. Such a high-silicon spheroidal graphite cast iron was heat treated up to 50 h in total at 800 °C in two clifferent manners: under isothermal and cyclic conditions. Under the isothermal condition, the distribution of graphite inclusions did not vary significantly. On the contrary, temperature cycling led to spectactùar coalescence whose evolution was observed after 1000, 2000 and 3000 cycles.Quite unexpectedly, the largest graphite particles - that were growing because of coalescence - showed an irregular outer surface after 1000 cycles, which evolved in impressive dendritic instabilities and then large protuberances after 2000 and 3000 cycles. Optical microscopy andX -ray computed tomography (XCT) were used to quantitatively study these microstructural changes

Sine-Gordon Model - Renormalization Group Solutions and Applications

The sine-Gordon model is discussed and analyzed within the framework of the renormalization group theory. A perturbative renormalization group procedure is carried out through a decomposition of the sine-Gordon field in slow and fast modes. An effective slow modes's theory is derived and re-scaled to obtain the model's flow equations. The resulting Kosterlitz-Thouless phase diagram is obtained and discussed in detail. The theory's gap is estimated in terms of the sine-Gordon model paramaters. The mapping between the sine-Gordon model and models for interacting electrons in one dimension, such as the g-ology model and Hubbard model, is discussed and the previous renormalization group results, obtained for the sine-Gordon model, are thus borrowed to describe different aspects of Luttinger liquid systems, such as the nature of its excitations and phase transitions. The calculations are carried out in a thorough and pedagogical manner, aiming the reader with no previous experience with the sine-Gordon model or the renormalization group approach.Comment: 44 pages, 7 figure

Spheroidal graphite coalescence during thermal cycling in the ferritic domain of a high-silicon cast iron studied by optical microscopy and X-ray computed tomography

International audienceHigh-silicon cast irons remain ferritic at higher temperature than usual cast irons and present both better oxidation resistance and higher mechanical strength. Such a high-silicon spheroidal graphite cast iron was heat treated up to 50 h in total at 800 °C in two clifferent manners: under isothermal and cyclic conditions. Under the isothermal condition, the distribution of graphite inclusions did not vary significantly. On the contrary, temperature cycling led to spectactùar coalescence whose evolution was observed after 1000, 2000 and 3000 cycles.Quite unexpectedly, the largest graphite particles - that were growing because of coalescence - showed an irregular outer surface after 1000 cycles, which evolved in impressive dendritic instabilities and then large protuberances after 2000 and 3000 cycles. Optical microscopy andX -ray computed tomography (XCT) were used to quantitatively study these microstructural changes