Organic Superconductors: when correlations and magnetism walk in

This survey provides a brief account for the start of organic superconductivity motivated by the quest for high Tc superconductors and its development since the eighties'. Besides superconductivity found in 1D organics in 1980, progresses in this field of research have contributed to better understand the physics of low dimensional conductors highlighted by the wealth of new remarkable properties. Correlations conspire to govern the low temperature properties of the metallic phase. The contribution of antiferromagnetic fluctuations to the interchain Cooper pairing proposed by the theory is borne out by experimental investigations and supports supercondutivity emerging from a non Fermi liquid background. Quasi one dimensional organic superconductors can therefore be considered as simple prototype systems for the more complex high Tc materials.Comment: 41 pages, 21 figures to be published in Journal of Superconductivity and Novel Magnetis

Transition metal alloys

A particular interest in the properties of transition metal alloys at the present time is the problem of the occurrence of localised electron spins. There is also, particularly in the first period, the problem of ordered magnetic states. Recent work has established that suppression of localised spin may occur in materials with a high density of states at the Fermi level, through the agency of combining those conduction states (with their balanced spin occupation) with the local state favoured by the impurity atom. The density of states, however, is not a sufficient discriminating parameter, and additional properties, such as the high susceptibility of e.g. Pd, play an important role in stabilising magnetic atomic states. Ferromagnetism on the band model is favoured by a high density of states, originating from the d-band. A high density of conduction states, however, suppresses spin moment on impurity atom, by broadening the d-states considerably and favouring equal spin occupation. Very particular interest, therefore, attaches to the properties of alloys at concentrations where ferromagnetic behaviour begins, such as vanadium-iron between 15 % and 25 % Fe.Une propriété intéressante des alliages de métaux de transition est actuellement l'existence de spins électroniques localisés. Il y a aussi, particulièrement dans la première période, le problème des états magnétiques ordonnées. Des travaux récents ont établi que les spins localisés peuvent disparaître dans les matériaux ayant une forte densité d'états au niveau de Fermi, par combinaison de ces états de conduction (qui sont également acceptés pour les deux directions de spin) avec l'état localisé favorisé par l'atome d'impureté. Cependant la densité d'états n'est pas un paramètre assez déterminant, et des propriétés additionnelles, telles que la forte susceptibilité, dans le cas du palladium par exemple, jouent un rôle important dans la stabilisation des états atomiques magnétiques. Dans le modèle des bandes, le ferromagnétisme est favorisé par une grande densité d'états, venant de la bande d. Cependant une forte densité d'états de conduction supprime le moment de spin sur les atomes d'impuretés, en élargissant considérablement les états d et en favorisant des populations égales de spin. Il est done particulièrement intéressant d'étudier les propriétés des alliages aux concentrations où commence à apparaitre le comportement ferromagnétiques, par exemple V-Fe entre 15 % et 25 % de fer

The fermi surface of palladium

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Evolution of Relationships Between Dislocation Microstructures and Internal Stresses of AISI 316L During Cyclic Loading at 293 K and 573 K (20 °C and 300 °C)

The evolution of dislocation densities and of dislocation microstructures during cyclic loading of AISI 316L is systematically evaluated. In addition, internal stresses are also measured for every cycle and comprehensively analyzed. These observations are made in order to establish relationships between the evolution of dislocation condition and internal stresses, and ultimately to obtain a thorough insight into the complex cyclic response of AISI 316L. Moreover, the dependencies of established relationships on the variation of temperature and strain amplitude are investigated. The back stresses (long-range stresses associated with the presence of collective dislocations over different length scales) are mainly responsible for the cyclic deformation response at high strain amplitudes where dislocations tend to move more quickly in a wavy manner. In contrast, the effective stress, coupling with short-range dislocation interactions, plays an insignificant role on the material cyclic response for wavy slip conditions, but increasingly becomes more important for planar slip conditions. The additionally strong short-range interactions between dislocations and point defects (initially with solute atoms and later in life with corduroy structure) at 573 K (300 °C) cause dislocations to move in more planar ways, resulting in a significant increase in effective stress, leading to their influential role on the material cyclic response.ISSN:1073-5623ISSN:1543-194