7,099 research outputs found

    Spiral phases and two-particle bound states from a systematic low-energy effective theory for magnons, electrons, and holes in an antiferromagnet

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    We have constructed a systematic low-energy effective theory for hole- and electron-doped antiferromagnets, where holes reside in momentum space pockets centered at (±π2a,±π2a)(\pm\frac{\pi}{2a},\pm\frac{\pi}{2a}) and where electrons live in pockets centered at (πa,0)(\frac{\pi}{a},0) or (0,πa)(0,\frac{\pi}{a}). The effective theory is used to investigate the magnon-mediated binding between two holes or two electrons in an otherwise undoped system. We derive the one-magnon exchange potential from the effective theory and then solve the corresponding two-quasiparticle Schr\"odinger equation. As a result, we find bound state wave functions that resemble dx2−y2d_{x^2-y^2}-like or dxyd_{xy}-like symmetry. We also study possible ground states of lightly doped antiferromagnets.Comment: 2 Pages; Proc. of SCES'07, Housto

    Ionization signals from electrons and alpha-particles in mixtures of liquid Argon and Nitrogen - perspectives on protons for Gamma Resonant Nuclear Absorption applications

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    In this paper we report on a detailed study of ionization signals produced by Compton electrons and alpha-particles in a Time Projection Chamber (TPC) flled with different mixtures of liquid Argon and Nitrogen. The measurements were carried out with Nitrogen concentrations up to 15% and a drift electric feld in the range 0-50 kV/cm. A prediction for proton ionization signals is made by means of interpolation. This study has been conducted in view of the possible use of liquid Ar-N2 TPCs for the detection of gamma-rays in the resonant band of the Nitrogen absorption spectrum, a promising technology for security and medical applications

    30 kV coaxial vacuum-tight feedthrough for operation at cryogenic temperatures

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    In this paper we describe the technology of building a vacuum-tight high voltage feedthrough which is able to operate at voltages up to 30 kV. The feedthrough has a coaxial structure with a grounded sheath which makes it capable to lead high voltage potentials into cryogenic liquids, without risk of surface discharges in the gas phase above the liquid level. The feedthrough is designed to be used in ionization detectors, based on liquefied noble gases, such as Argon or Xenon
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