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

Origin of the gap in the surface states of the antiferromagnetic topological insulator

We study the influence of the antiferromagnetic order on the surface states of topological insulators. We derive an effective Hamiltonian for these states, taking into account the space structure of the antiferromagnetic ordering. We obtain a typical (gapless) Dirac Hamiltonian for the surface states if the surface of the sample is not perturbed. However, a shift in the chemical potential of the surface layer opens a gap in the spectrum away from Fermi energy. Such a gap arises only in systems with a finite antiferromagnetic order. We observe that the gap is robust against the surface disorder. The obtained results are consistent with the recent experiments and density functional theory calculations.Comment: 6 pages, 3 figure