A Model with Propagating Spinons beyond One Dimension

For the model of frustrated spin-1/2 Heisenberg magnet described in A. A. Nersesyan and A. M. Tsvelik, (Phys. Rev. B{\bf 67}, 024422 (2003)) we calculate correlation functions of staggered magnetization and dimerization. The model is formulated as a collection of antiferromagnetic chains weakly coupled by a frustrated exchange interaction. The calculation done for the case of four chains demonstrates that these functions do not vanish. Since the correlation functions in question factorize into a product of correlation functions of spinon creation and annihilation operators, this constitutes a proof that spinons in this model propagate in the direction perpendicular to the chains.Comment: revised version to appear in Phys. Rev B., 8 pages, a reference adde

Estimating Poverty for Indigenous Groups in Chile by Matching Census and Survey Data

It is widely held that indigenous Chileans experience greater rates of poverty and indigence than non-indigenous Chileans, yet the evidence to date has been based on surveys that are not representative by ethnicity. In this paper, we use poverty mapping methodologies that are typically applied to geography to develop statistically precise estimates of poverty, indigence, poverty gaps, and indigence gaps for each of the eight indigenous groups recognized by Chilean law. We find that indigenous people experience higher rates of poverty and indigence and greater depth of poverty and indigence than non-indigenous people. These results hold within individual regions, suggesting that the differential access to economic opportunities in different parts of the country cannot fully explain the results. We also find that the burden of poverty is not shared equally across indigenous groups. Instead, the Mapuche and Aymar· experience disproportionately high poverty rates. We argue that including ethnicity in criteria for identifying poor households may help policy-makers to improve antipoverty targeting.http://deepblue.lib.umich.edu/bitstream/2027.42/64360/1/wp932.pd

Estimating Poverty for Indigenous Groups in Chile by Matching Census and Survey Data

It is widely held that indigenous Chileans experience greater rates of poverty and indigence than non-indigenous Chileans, yet the evidence to date has been based on surveys that are not representative by ethnicity. In this paper, we use poverty mapping methodologies that are typically applied to geography to develop statistically precise estimates of poverty, indigence, poverty gaps, and indigence gaps for each of the eight indigenous groups recognized by Chilean law. We find that indigenous people experience higher rates of poverty and indigence and greater depth of poverty and indigence than non-indigenous people. These results hold within individual regions, suggesting that the differential access to economic opportunities in different parts of the country cannot fully explain the results. We also find that the burden of poverty is not shared equally across indigenous groups. Instead, the Mapuche and Aymará experience disproportionately high poverty rates. We argue that including ethnicity in criteria for identifying poor households may help policy-makers to improve antipoverty targeting.Poverty; Indigence; Ethnicity; Poverty Mapping; Chile

Signature of Schwinger's pair creation rate via radiation generated in graphene by strong electric current

Electron - hole pairs are copuously created by an applied electric field near the Dirac point in graphene or similar 2D electronic systems. It was shown recently that for sufficiently large electric fields and ballistic times the I-V characteristics become strongly nonlinear due to Schwinger's pair creation. Since there is no energy gap the radiation from the pairs' annihilation is enhanced. The spectrum of radiation is calculated. The angular and polarization dependence of the emitted photons with respect to the graphene sheet is quite distinctive. For very large currents the recombination rate becomes so large that it leads to the second Ohmic regime due to radiation friction.Comment: 9 pages, 7 figure

Colloquium: Physics of optical lattice clocks

Recently invented and demonstrated, optical lattice clocks hold great promise for improving the precision of modern timekeeping. These clocks aim at the 10^-18 fractional accuracy, which translates into a clock that would neither lose or gain a fraction of a second over an estimated age of the Universe. In these clocks, millions of atoms are trapped and interrogated simultaneously, dramatically improving clock stability. Here we discuss the principles of operation of these clocks and, in particular, a novel concept of "magic" trapping of atoms in optical lattices. We also highlight recently proposed microwave lattice clocks and several applications that employ the optical lattice clocks as a platform for precision measurements and quantum information processing.Comment: 18 pages, 15 figure

Elastic systems with correlated disorder: Response to tilt and application to surface growth

We study elastic systems such as interfaces or lattices pinned by correlated quenched disorder considering two different types of correlations: generalized columnar disorder and quenched defects correlated as ~ x^{-a} for large separation x. Using functional renormalization group methods, we obtain the critical exponents to two-loop order and calculate the response to a transverse field h. The correlated disorder violates the statistical tilt symmetry resulting in nonlinear response to a tilt. Elastic systems with columnar disorder exhibit a transverse Meissner effect: disorder generates the critical field h_c below which there is no response to a tilt and above which the tilt angle behaves as \theta ~ (h-h_c)^{\phi} with a universal exponent \phi<1. This describes the destruction of a weak Bose glass in type-II superconductors with columnar disorder caused by tilt of the magnetic field. For isotropic long-range correlated disorder, the linear tilt modulus vanishes at small fields leading to a power-law response \theta ~ h^{\phi} with \phi>1. The obtained results are applied to the Kardar-Parisi-Zhang equation with temporally correlated noise.Comment: 15 pages, 8 figures, revtex

A novel platform for two-dimensional chiral topological superconductivity

We show that the surface of an $s$-wave superconductor decorated with a two-dimensional lattice of magnetic impurities can exhibit chiral topological superconductivity. If impurities order ferromagnetically and the superconducting surface supports a sufficiently strong Rashba-type spin-orbit coupling, Shiba sub-gap states at impurity locations can hybridize into Bogoliubov bands with non-vanishing, sometimes large, Chern number $C$. This topological superconductor supports $C$ chiral Majorana edge modes. We construct phase diagrams for model two-dimensional superconductors, accessing the dilute and dense magnetic impurity limits analytically and the intermediate regime numerically. To address potential experimental systems, we identify stable configurations of ferromagnetic iron atoms on the Pb (111) surface and conclude that ferromagnetic adatoms on Pb surfaces can provide a versatile platform for two-dimensional topological superconductivity

Bi-HKT and bi-Kaehler supersymmetric sigma models

We study CKT (or bi-HKT) N = 4 supersymmetric quantum mechanical sigma models. They are characterized by the usual and the mirror sectors displaying each HKT geometry. When the metric involves isometries, a Hamiltonian reduction is possible. The most natural such reduction with respect to a half of bosonic target space coordinates produces an N = 4 model, related to the twisted Kaehler model due to Gates, Hull and Rocek, but including certain extra F-terms in the superfield action.Comment: 31 pages, minor corrections in the published versio

Statics and dynamics of elastic manifolds in media with long-range correlated disorder

We study the statics and dynamics of an elastic manifold in a disordered medium with quenched defects correlated as r^{-a} for large separation r. We derive the functional renormalization-group equations to one-loop order, which allow us to describe the universal properties of the system in equilibrium and at the depinning transition. Using a double epsilon=4-d and delta=4-a expansion, we compute the fixed points characterizing different universality classes and analyze their regions of stability. The long-range disorder-correlator remains analytic but generates short-range disorder whose correlator exhibits the usual cusp. The critical exponents and universal amplitudes are computed to first order in epsilon and delta at the fixed points. At depinning, a velocity-versus-force exponent beta larger than unity can occur. We discuss possible realizations using extended defects.Comment: 16 pages, 11 figures, revtex