An X‐ray magnetic circular dichroism (XMCD) study performed at the rare‐earth L2,3‐edges in the RxR1?x′Al2 compounds is presented. It is shown that both R and R′ atoms contribute to the XMCD recorded at the L‐edges of the selected rare‐earth, either R or R′. The amplitude of the XMCD signal is not directly correlated to the magnetization or to the value of the individual (R, R′) magnetic moments, but it is related to the molecular field acting on the rare‐earth tuned in the photoabsorption process. This result closes a longstanding study of the origin of the XMCD at the L‐edge of the rare‐earths in multi‐component systems, allowing a full understanding of the exact nature of these signals. 相似文献
A one-dimensional diagonal tight binding electronic system is analyzed with the Hamiltonian map approach to study analytically
the inverse localization length of an infinite sample. Both the uncorrelated and the dichotomic correlated random potential
sequences are considered in the evaluations of the inverse localization length. Analytical expressions for the invariant measure
or the angle density distribution are the main motivation of this work in order to derive analytical results. The well-known
uncorrelated weak disorder result of the inverse localization length is derived with a clear procedure. In addition, an analytical
expression for high disorder is obtained near the band edge. It is found that the inverse localization length goes to 1 in
this limit. Following the procedure used in the uncorrelated situation, an analytical expression for the inverse localization
length is also obtained for the dichotomic correlated sequence in the small disorder situation. 相似文献
For a given graph consider a pair of disjoint matchings the union of which contains as many edges as possible. Furthermore, consider the ratio of the cardinalities of a maximum matching and the largest matching in those pairs. It is known that for any graph is the tight upper bound for this ratio. We characterize the class of graphs for which it is precisely . Our characterization implies that these graphs contain a spanning subgraph, every connected component of which is the minimal graph of this class. 相似文献
By performing density functional theory calculations, we studied the quantum confinement in charged graphene quantum dots (GQDs), which is found to be clearly edge and shape dependent. It is found that the excess charges have a large distribution at the edges of the GQD. The resulting energy spectrum shift is very nonuniform and hence the Coulomb diamonds in the charge stability diagram vary irregularly, in good agreement with the observed nonperiodic Coulomb blockade oscillation. We also illustrate that the level statistics of the GQDs can be described by a Gaussian distribution, as predicted for chaotic Dirac billiards.