Generation of localized magnetic moments in the charge-density-wave state

We propose a mechanism explaining the generation of localized magnetic moments in charge-density-wave compounds. Our model Hamiltonian describes an Anderson impurity placed in a host material exhibiting the charge-density wave. There is a region of the model's parameter space, where even weak Coulomb repulsion on the impurity site is able to localize the magnetic moment on the impurity. The phase diagram of a single impurity at T=0 is mapped. To establish the connection with experiment thermodynamic properties of a random impurity ensemble is studied. Magnetic susceptibility of the ensemble diverges at low temperature; heat capacity as a function of the magnetic field demonstrates pronounced low field peak. Both features are consistent with experiments on orthorhombic TaS3 and blue bronze.Comment: 8 pages, 7 figure

О построении циркулянтных матриц, связанных с MDS-матрицами

The objective of this paper is to suggest a method of the construction of circulant ma-trices, which are appropriate for being MDS (Maximum Distance Separable) matrices utilising in cryptography. Thus, we focus on designing so-called bi-regular circulant matrices, and furthermore, impose additional restraints on matrices in order that they have the maximal number of some element occurrences and the minimal number of distinct elements. The reason to construct bi-regular matrices is that any MDS matrix is necessarily the bi-regular one, and two additional restraints on matrix elements grant that matrix-vector multiplication for the samples constructed may be performed effciently. The results obtained include an upper bound on the number of some ele-ment occurrences for which the circulant matrix is bi-regular. Furthermore, necessary and sucient conditions for the circulant matrix bi-regularity are derived. On the ba-sis of these conditions, we developed an effcient bi-regularity verication procedure. Additionally, several bi-regular circulant matrix layouts of order up to 31 with the maximal number of some element occurrences are listed. In particular, it appeared that there are no layouts of order 32 with more than 5 occurrences of any element which yield a bi-regular matrix (and hence an MDS matrix)

Influence of the particle shape on the equilibrium morphologies of supracolloidal magnetic filaments

We investigate the equilibrium morphologies of linear and ring-shaped magnetic filaments made from crosslinked ferromagnetic spherical or ellipsoidal colloidal particles. Using Langevin dynamics simulations, we calculate the radius of gyration and total magnetic moment of a single filament at zero field and different temperatures, analyzing the influence of the particles shape, the strength of their magnetic moment and the filament length. Our results show that, among such parameters, the shape of the particles has the strongest qualitative impact on the equilibrium behavior of the filaments

Electronic properties of the armchair graphene nanoribbon

We investigate the electronic band structure of an undoped graphene armchair nanoribbon. We demonstrate that such nanoribbon always has a gap in its electronic spectrum. Indeed, even in the situations where simple single-electron calculations predict a metallic dispersion, the system is unstable with respect to the deformation of the carbon-carbon bonds dangling at the edges of the armchair nanoribbon. The edge bonds' deformation couples electron and hole states with equal momentum. This coupling opens a gap at the Fermi level. In a realistic sample, however, it is unlikely that this instability could be observed in its pure form. Namely, since chemical properties of the dangling carbon atoms are different from chemical properties of the atoms inside the sample (for example, the atoms at the edge have only two neighbours, besides additional non-carbon atoms might be attached to passivate unpaired covalent carbon bonds), it is very probable that the bonds at the edge are deformed due to chemical interactions. This chemically-induced modification of the nanoribbon's edges can be viewed as an effective field biasing our predicted instability in a particular direction. Yet by disordering this field (e.g., through random substitution of the radicals attached to the edges) we may tune the system back to the critical regime and vary the electronic properties of the system. For example, we show that electrical transport through a nanoribbon is strongly affected by such disorder.Comment: 12 pages, 4 figur