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

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

Atomically thin dilute magnetism in Co-doped phosphorene

Two-dimensional dilute magnetic semiconductors can provide fundamental insights in the very nature of magnetic orders and their manipulation through electron and hole doping. Despite the fundamental physics, due to the large charge density control capability in these materials, they can be extremely important in spintronics applications such as spin valve and spin-based transistors. In this article, we studied a two-dimensional dilute magnetic semiconductors consisting of phosphorene monolayer doped with cobalt atoms in substitutional and interstitial defects. We show that these defects can be stabilized and are electrically active. Furthermore, by including holes or electrons by a potential gate, the exchange interaction and magnetic order can be engineered, and may even induce a ferromagnetic-to-antiferromagnetic phase transition in p-doped phosphorene.Comment: 7 pages, 4 colorful figure

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