Nematic order in square lattice frustrated ferromagnets

We present a new scenario for the breakdown of ferromagnetic order in a two-dimensional quantum magnet with competing ferromagnetic and antiferromagnetic interactions. In this, dynamical effects lead to the formation of two-magnon bound states, which undergo Bose-Einstein condensation, giving rise to bond-centered nematic order. This scenario is explored in some detail for an extended Heisenberg model on a square lattice. In particular, we present numerical evidence confirming the existence of a state with d-wave nematic correlations but no long-range magnetic order, lying between the saturated ferromagnetic and collinear antiferromagnetic phases of the ferromagnetic model J1-J2. We argue by continuity of spectra that this phase is also present in a model with 4-spin cyclic exchange.     

Precision measurement with visual feedback using binary phase diffractive optical elements

A novel method for obtaining precision measurements by using two binary diffractive optical elements is presented. The system provides visual feedback of the measurement without the use of electronics.     

Monte Carlo study of half-magnetization plateau and magnetic phase diagram in pyrochlore antiferromagnetic Heisenberg model

The antiferromagnetic Heisenberg model on a pyrochlore lattice under external magnetic field is studied by classical Monte Carlo simulation. The model includes bilinear and biquadratic interactions; the latter effectively describes the coupling to lattice distortions. The magnetization process shows a half-magnetization plateau at low temperatures, accompanied with strong suppression of the magnetic susceptibility. Temperature dependence of the plateau behavior is clarified. Finite-temperature phase diagram under the magnetic field is determined. The results are compared with recent experimental results in chromium spinel oxides.     

Manifestation of the van der Waals surface interaction in the spontaneous emission of atoms into an optical nanofiber

We study the spontaneous emission of atoms near an optical nanofiber and analyze the coupling efficiency of the spontaneous emission into a nanofiber. We also investigate the influence of the van der Waals interaction of atoms with the surface of the optical nanofiber on the spectrum of coupled light. Using, as an example, ⁸⁵Rb atoms we show that the van der Waals interaction may considerably extend the red wing of the spontaneous emission line and, accordingly, produce a well-defined asymmetry of the spontaneous emission spectrum coupled into an optical nanofiber.     

Octupolar order in the multiple spin exchange model on a triangular lattice

We show how a gapless spin liquid with hidden octupolar order arises in an applied magnetic field, in a model applicable to thin films of 3He with competing ferromagnetic and antiferromagnetic (cyclic) exchange interactions. Evidence is also presented for nematic--i.e., quadrupolar--correlations bordering on ferromagnetism in the absence of a magnetic field.     

A W-Geometry Ortho-TOF MS with High Resolution and Up to 100% Duty Cycle for MS/MS

Orthogonal injection time-of-flight (orthoTOF) mass spectrometry (MS) is the most prevalent form of TOFMS, owing to its greater control over incoming ion energy, the ability to correct for aberrations in incoming ion velocity and position, and its ability to provide an entire mass spectrum within a single scan. However, the duty cycle of orthoTOFMS is low compared with scanning analyzers, which can have 100% duty cycle when measuring a single type of ion. Typical duty cycles for orthoTOFMS range from 1% to 30%, depending on instrument geometry. Generally, as instrument resolution increases, duty cycle decreases. Additionally, the greatest duty cycle is achieved for the highest m/z ion recorded in the spectrum, and decreases for all other ions as a function of m/z. In a prior publication [Loboda, A.V.; Chernushevich, I.V. J. Am. Soc. Mass Spectrom. 20, 1342–1348 (20)], a novel trapping/release method for restoring the duty cycle of a V-geometry orthoTOFMS to near 100% (referred to as “Zeno pulsing”) was presented. Here, we apply that method to a W-TOF geometry analyzer with analog detection. Across a m/z range of 100–2000, sensitivity gains of ~5–20 are observed, for total ion currents approaching ~10⁷ ions·s^?1. Zeno pulsing, or similar strategies for restoring duty cycle, will continue to be important as instrument resolution in orthoTOFMS is increased through the use of ion mirrors.

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Direct imaging of polyethylene films at single-chain resolution with torsional tapping atomic force microscopy

The physical properties of semicrystalline polymers depend on the organisation of chains within the crystal and amorphous regions, on the interface between the two, and on the location and nature of defects. Here, torsional tapping atomic force microscopy has been used to image crystalline lamellae and the crystal-amorphous-region interface at the single-chain level with resolution down to 3.7 ?. Defects within the crystalline phase, such as buried folds and chain ends, are revealed. Imaging at the chain level also allows direct measurement of crystalline stem lengths, providing a potential route to test theories of crystal thickness selection.     

Imaging of multiple linear cracks using impedance data

This paper develops a fast, simple algorithm for locating one or more perfectly insulating, pair-wise disjoint, linear cracks in a homogeneous two-dimensional electrical conductor, using flux-potential boundary measurements. We also explore the issue of what types boundary inputs yield the most stable images.     

The geometric invariants $${\Omega^{n}}$$ of a product of groups

We compute the geometric invariants of a product G × H of groups in terms of and . This gives a sufficient condition in terms of and for a normal subgroup of G × H with abelian quotient to be of type F _n . We give an example involving the direct product of the Baumslag–Solitar group BS_1,2 with itself.