Large magnetoresistance in the antiferromagnetic semi-metal NdSb

There has been considerable interest in topological semi-metals that exhibit extreme magnetoresistance (XMR). These have included materials lacking inversion symmetry such as TaAs, as well Dirac semi-metals such as Cd3As2. However, it was reported recently that LaSb and LaBi also exhibit XMR, even though the rock-salt structure of these materials has inversion symmetry, and the band-structure calculations do not show a Dirac dispersion in the bulk. Here, we present magnetoresistance and specific heat measurements on NdSb, which is isostructural with LaSb. NdSb has an antiferromagnetic groundstate, and in analogy with the lanthanum monopnictides, is expected to be a topologically non-trivial semi-metal. We show that NdSb has an XMR of 10^4 %, even within the AFM state, illustrating that XMR can occur independently of the absence of time reversal symmetry breaking in zero magnetic field. The persistence of XMR in a magnetic system offers promise of new functionality when combining topological matter with electronic correlations. We also find that in an applied magnetic field below the Neel temperature there is a first order transition, consistent with evidence from previous neutron scattering work.Comment: 5 pages, 6 figure

Stress engineering at the nanometer scale: Two-component adlayer stripes

Spontaneously formed equilibrium nanopatterns with long-range order are widely observed in a variety of systems, but their pronounced temperature dependence remains an impediment to maintain such patterns away from the temperature of formation. Here, we report on a highly ordered stress-induced stripe pattern in a two-component, Pd-O, adsorbate monolayer on W(110), produced at high temperature and identically preserved at lower temperatures. The pattern shows a tunable period (down to 16 nm) and orientation, as predicted by a continuum model theory along with the surface stress and its anisotropy found in our DFT calculations. The control over thermal fluctuations in the stripe formation process is based on the breaking/restoring of ergodicity in a high-density lattice gas with long-range interactions upon turning off/on particle exchange with a heat bath.Comment: 6 pages, 4 figure

Singular vectors by Fusions in affine su(2)

Explicit expressions for the singular vectors in the highest weight representations of $A_1^{(1)}$ are obtained using the fusion formalism of conformal field theory.Comment: 7 page

Quantum-Well Wavefunction Localization and the Electron-Phonon Interaction in Thin Ag Nanofilms

The electron-phonon interaction in thin Ag-nanofilms epitaxially grown on Cu(111) is investigated by temperature-dependent and angle-resolved photoemission from silver quantum-well states. Clear oscillations in the electron-phonon coupling parameter as a function of the silver film thickness are observed. Different from other thin film systems where quantum oscillations are related to the Fermi-level crossing of quantum-well states, we can identify a new mechanism behind these oscillations, based on the wavefunction localization of the quantum-well states in the film

Towards pair production near threshold with unstable particle effective theory

We illustrate the use of effective theory techniques to describe processes involving unstable particles close to resonance. First, we present the main ideas in the context of a scalar resonance in an Abelian gauge-Yukawa model. We then outline the necessary modifications to describe W-pair production close to threshold in electron-positron collisions.Comment: Invited talk given at the 11th International Conference on QCD, Montpellier, France (5--10th July 2004

Dynamic charge inhomogenity in cuprate superconductors

The inelastic x-ray scattering spectrum for phonons of $\Delta_{1}$-symmetry including the CuO bond-stretching phonon dispersion is analyzed by a Lorentz fit in HgBa$_{2}$CuO$_{4}$ and Bi$_{2}$Sr$_{2}$CuO$_{6}$, respectively, using recently calculated phonon frequencies as input parameters. The resulting mode frequencies of the fit are almost all in good agreement with the calculated data. An exception is the second highest $\Delta_{1}$-branch compromising the bond-stretching modes which disagrees in both compounds with the calculations. This branch unlike the calculations shows an anomalous softening with a minimum around the wavevector \vc{q}=\frac{2\pi}{a}(0.25, 0, 0). Such a disparity with the calculated results, that are based on the assumption of an undisturbed translation- and point group invariant electronic structure of the CuO plane, indicates some {\it static} charge inhomogenities in the measured probes. Most likely these will be charge stripes along the CuO bonds which have the strongest coupling to certain longitudinal bond-stretching modes that in turn selfconsistently induce corresponding {\it dynamic} charge inhomogenities. The symmetry breaking by the mix of dynamic and static charge inhomogenities can lead to a reconstruction of the Fermi surface into small pockets.Comment: 7 pages, 4 figure

Phase Transition with the Berezinskii--Kosterlitz--Thouless Singularity in the Ising Model on a Growing Network

We consider the ferromagnetic Ising model on a highly inhomogeneous network created by a growth process. We find that the phase transition in this system is characterised by the Berezinskii--Kosterlitz--Thouless singularity, although critical fluctuations are absent, and the mean-field description is exact. Below this infinite order transition, the magnetization behaves as $exp(-const/\sqrt{T_c-T})$. We show that the critical point separates the phase with the power-law distribution of the linear response to a local field and the phase where this distribution rapidly decreases. We suggest that this phase transition occurs in a wide range of cooperative models with a strong infinite-range inhomogeneity. {\em Note added}.--After this paper had been published, we have learnt that the infinite order phase transition in the effective model we arrived at was discovered by O. Costin, R.D. Costin and C.P. Grunfeld in 1990. This phase transition was considered in the papers: [1] O. Costin, R.D. Costin and C.P. Grunfeld, J. Stat. Phys. 59, 1531 (1990); [2] O. Costin and R.D. Costin, J. Stat. Phys. 64, 193 (1991); [3] M. Bundaru and C.P. Grunfeld, J. Phys. A 32, 875 (1999); [4] S. Romano, Mod. Phys. Lett. B 9, 1447 (1995). We would like to note that Costin, Costin and Grunfeld treated this model as a one-dimensional inhomogeneous system. We have arrived at the same model as a one-replica ansatz for a random growing network where expected to find a phase transition of this sort based on earlier results for random networks (see the text). We have also obtained the distribution of the linear response to a local field, which characterises correlations in this system. We thank O. Costin and S. Romano for indicating these publications of 90s.Comment: 5 pages, 2 figures. We have added a note indicating that the infinite order phase transition in the effective model we arrived at was discovered in the work: O. Costin, R.D. Costin and C.P. Grunfeld, J. Stat. Phys. 59, 1531 (1990). Appropriate references to the papers of 90s have been adde

Information Extraction in Illicit Domains

Extracting useful entities and attribute values from illicit domains such as human trafficking is a challenging problem with the potential for widespread social impact. Such domains employ atypical language models, have `long tails' and suffer from the problem of concept drift. In this paper, we propose a lightweight, feature-agnostic Information Extraction (IE) paradigm specifically designed for such domains. Our approach uses raw, unlabeled text from an initial corpus, and a few (12-120) seed annotations per domain-specific attribute, to learn robust IE models for unobserved pages and websites. Empirically, we demonstrate that our approach can outperform feature-centric Conditional Random Field baselines by over 18\% F-Measure on five annotated sets of real-world human trafficking datasets in both low-supervision and high-supervision settings. We also show that our approach is demonstrably robust to concept drift, and can be efficiently bootstrapped even in a serial computing environment.Comment: 10 pages, ACM WWW 201