In-gap impurity states as the hallmark of the Quantum Spin Hall phase

We study the different response to an impurity of the two topologically different phases shown by a two dimensional insulator with time reversal symmetry, namely, the Quantum Spin Hall and the normal phase. We consider the case of graphene as a toy model that features the two phases driven, respectively, by intrinsic spin-orbit coupling and inversion symmetry breaking. We find that strictly normalizable in-gap impurity states only occur in the Quantum Spin Hall phase and carry dissipationless current whose quirality is determined by the spin and pseudospin of the residing electron. Our results imply that topological order can be unveiled by local probes of defect states.Comment: 5 pages, 3 figure

Marginal Fermi liquid behavior from 2d Coulomb interaction

A full, nonperturbative renormalization group analysis of interacting electrons in a graphite layer is performed, in order to investigate the deviations from Fermi liquid theory that have been observed in the experimental measures of a linear quasiparticle decay rate in graphite. The electrons are coupled through Coulomb interactions, which remain unscreened due to the semimetallic character of the layer. We show that the model flows towards the noninteracting fixed-point for the whole range of couplings, with logarithmic corrections which signal the marginal character of the interaction separating Fermi liquid and non-Fermi liquid regimes.Comment: 7 pages, 2 Postscript figure

Parity violation in quasielastic electron-nucleus scattering within the relativistic impulse approximation

We study parity violation in quasielastic (QE) electron-nucleus scattering using the relativistic impulse approximation. Different fully relativistic approaches have been considered to estimate the effects associated with the final-state interactions. We have computed the parity-violating quasielastic (PVQE) asymmetry and have analyzed its sensitivity to the different ingredients that enter in the description of the reaction mechanism: final-state interactions, nucleon off-shellness effects, current gauge ambiguities. Particular attention has been paid to the description of the weak neutral current form factors. The PVQE asymmetry is proven to be an excellent observable when the goal is to get precise information on the axial-vector sector of the weak neutral current. Specifically, from measurements of the asymmetry at backward scattering angles good knowledge of the radiative corrections entering in the isovector axial-vector sector can be gained. Finally, scaling properties shown by the interference $\gamma-Z$ nuclear responses are also analyzed.Comment: 15 pages, 11 figure

Electron Confinement Induced by Diluted Hydrogen-like Ad-atoms in Graphene Ribbons

We report the electronic properties of two-dimensional systems made of graphene nanoribbons which are patterned with ad-atoms in two separated regions. Due to the extra electronic confinement induced by the presence of the impurities, we find resonant levels, quasi-bound and impurity-induced localized states, which determine the transport properties of the system. Regardless of the ad-atom distribution in the system, we apply band-folding procedures to simple models and predict the energies and the spatial distribution of those impurity-induced states. We take into account two different scenarios: gapped graphene and the presence of randomly distributed ad-atoms in a low dilution regime. In both cases the defect-induced resonances are still detected. Our findings would encourage experimentalist to synthesize these systems and characterize their quasi-localized states employing, for instance, scanning tunneling spectroscopy (STS). Additionally, the resonant transport features could be used in electronic applications and molecular sensor devices.Comment: 12 pages, 11 figures, submitted (minor changes

Parity violation and dynamical relativistic effects in (e⃗,e′N)(\vec{e},e'N) reactions

It is well known that coincidence quasielastic $(\vec{e},e'N)$ reactions are not appropriate to analyze effects linked to parity violation due the presence of the fifth electromagnetic (EM) response $R^{TL'}$. Nevertheless, in this work we develop a fully relativistic approach to be applied to parity-violating (PV) quasielastic $(\vec{e},e'N)$ processes. This is of importance as a preliminary step in the subsequent study of inclusive quasielastic PV $(\vec{e},e')$ reactions. Moreover, our present analysis allows us to disentangle effects associated with the off-shell character of nucleons in nuclei, gauge ambiguities and the role played by the lower components in the nucleon wave functions, i.e., dynamical relativistic effects. This study can help in getting clear information on PV effects. Particular attention is paid to the relativistic plane-wave impulse approximation where the explicit expressions for the PV single-nucleon responses are shown for the first time.Comment: 39 pages, 9 figure

Global analysis of parity-violating asymmetry data for elastic electron scattering

We perform a statistical analysis of the full set of parity-violating asymmetry data for elastic electron scattering including the most recent high precision measurement from $Q$-weak. Given the basis of the present analysis, our estimates appear to favor non-zero vector strangeness, specifically, positive (negative) values for the electric (magnetic) strange form factors. We also provide an accurate estimate of the axial-vector nucleon form factor at zero momentum transfer, $G_A^{ep}(0)$. Our study shows $G_A^{ep}(0)$ to be importantly reduced with respect to the currently accepted value. We also find our analysis of data to be compatible with the Standard Model values for the weak charges of the proton and neutron.Comment: 6 pages, 4 figures, 2 tables. Accepted for publication in PR

Confinement of electrons in layered metals

We analyze the out of plane hopping in models of layered systems where the in--plane properties deviate from Landau's theory of a Fermi liquid. We show that the hopping term acquires a non trivial energy dependence, due to the coupling to in plane excitations, and can be either relevant or irrelevant at low energies or temperatures. The latter is always the case if the Fermi level lies close to a saddle point in the dispersion relation.Comment: 4 pages, 1 eps figur