Density dependent spin susceptibility and effective mass in interacting quasi-two dimensional electron systems

Motivated by recent experimental reports, we carry out a Fermi liquid many-body calculation of the interaction induced renormalization of the spin susceptibility and effective mass in realistic two dimensional (2D) electron systems as a function of carrier density using the leading-order `ladder-bubble' expansion in the dynamically screened Coulomb interaction. Using realistic material parameters for various semiconductor-based 2D systems, we find reasonable quantitative agreement with recent experimental susceptibility and effective mass measurements. We point out a number of open questions regarding quantitative aspects of the comparison between theory and experiment in low-density 2D electron systems

The quasiparticle spectral function in doped graphene

We calculate the real and imaginary electron self-energy as well as the quasiparticle spectral function in doped graphene taking into account electron-electron interaction in the leading order dynamically screened Coulomb coupling. Our theory provides the basis for calculating {\it all} one-electron properties of extrinsic graphene. Comparison with existing ARPES measurements shows broad qualitative agreement between theory and experiment. We also calculate the renormalized graphene momentum distribution function, finding a typical Fermi liquid discontinuity at k_F. We also provide a critical discussion of the relevant many body approximations (e.g. RPA) for graphene.Comment: 5 pages, 3 figure

Ab-initio study of disorder effects on the electronic and magnetic structures of Sr2_2FeMoO6_6

We have investigated the electronic structure of ordered and disordered Sr$_2$FeMoO$_6$ using {\it ab-initio} band structure methods. The effect of disorder was simulated within super-cell calculations to realize several configurations with mis-site disorders. It is found that such disorder effects destroy the half-metallic ferro-magnetic state of the ordered compound. It also leads to a substantial reduction of the magnetic moments at the Fe sites in the disordered configurations. Most interestingly, it is found for the disordered configurations, that the magnetic coupling within the Fe sub-lattice as well as that within the Mo sub-lattice always remain ferro-magnetic, while the two sub-lattices couple anti-ferromagnetically, in close analogy to the magnetic structure of the ordered compound, but in contrast to recent suggestions.Comment: 7 pages, 3 figure

Compressibility of graphene

We develop a theory for the compressibility and quantum capacitance of disordered monolayer and bilayer graphene including the full hyperbolic band structure and band gap in the latter case. We include the effects of disorder in our theory, which are of particular importance at the carrier densities near the Dirac point. We account for this disorder statistically using two different averaging procedures: first via averaging over the density of carriers directly, and then via averaging in the density of states to produce an effective density of carriers. We also compare the results of these two models with experimental data, and to do this we introduce a model for inter-layer screening which predicts the size of the band gap between the low-energy conduction and valence bands for arbitary gate potentials applied to both layers of bilayer graphene. We find that both models for disorder give qualitatively correct results for gapless systems, but when there is a band gap at charge neutrality, the density of states averaging is incorrect and disagrees with the experimental data.Comment: 10 pages, 7 figures, RevTe