Luttinger Stripes in Antiferromagnets

We propose a model for the physics of stripes in antiferromagnets in which the stripes are described by Luttinger liquids hybridized with antiferromagnetic domains. Using bosonization techniques we study the model in the limit where the magnetic correlation length is larger than the inter-stripe distance and propose an explanation for the commensurate-incommensurate phase transition seen in neutron scattering in the underdoped regime of La_{2-x} Sr_x Cu O_4. The explanation is based on a phase to anti-phase domain transition in the spin configuration which is associated with the transverse motion of the stripes. Using a non-linear sigma model to describe the antiferromagnetic regions we conjecture the crystalization of the stripes in the magnetically ordered phase.Comment: 9 pages, Revtex, Epsf, 4 figures. To appear in the Proceedings of the Euroconference on "Correlations in unconventional quantum liquids" in Zeitschrift f\"ur Physik B - Condensed Matter (dedicated to the memory of Sir Rudolph Peierls

Conductivity of suspended and non-suspended graphene at finite gate voltage

We compute the DC and the optical conductivity of graphene for finite values of the chemical potential by taking into account the effect of disorder, due to mid-gap states (unitary scatterers) and charged impurities, and the effect of both optical and acoustic phonons. The disorder due to mid-gap states is treated in the coherent potential approximation (CPA, a self-consistent approach based on the Dyson equation), whereas that due to charged impurities is also treated via the Dyson equation, with the self-energy computed using second order perturbation theory. The effect of the phonons is also included via the Dyson equation, with the self energy computed using first order perturbation theory. The self-energy due to phonons is computed both using the bare electronic Green's function and the full electronic Green's function, although we show that the effect of disorder on the phonon-propagator is negligible. Our results are in qualitative agreement with recent experiments. Quantitative agreement could be obtained if one assumes water molelcules under the graphene substrate. We also comment on the electron-hole asymmetry observed in the DC conductivity of suspended graphene.Comment: 13 pages, 11 figure

Comment on "BCS superconductivity of Dirac fermions in graphene layers"

Comment on "BCS superconductivity of Dirac fermions in graphene layers" by N. B. Kopnin and E. B. Sonin [arXiv:0803.3772; Phys. Rev. Lett. 100, 246808 (2008)].Comment: 1.1 page

Doped planar quantum antiferromagnets with striped phases

We study the properties of the striped phases that have been proposed for the doped cuprate planar quantum antiferromagnets. We invoke an effective, spatially anisotropic, non-linear sigma model in two space dimensions. Our theoretical predictions are in {\it quantitative} agreement with recent experiments. We focus on (i) the staggered magnetization at $T=0$ and (ii) the N\'eel temperature, as functions of doping; these have been measured recently in La${}_{2-x}$ Sr${}_x$ Cu O${}_4$ with $0 \leq x \leq 0.018$. Good agreement with experiment is obtained using parameters determined previously and independently for this system. These results support the proposal that the low doping (antiferromagnetic) phase of the cuprates has a striped configuration.Comment: 4 pages, RevteX, 2 figures, new references added, minor changes in wording and corrections of some formula