Unstable elementary excitations in a quantum magnet at high fields
A quantum magnetic system makes up a world of its own having both
elementary particles and forces acting between them. In this paper, we
have shown that the elementary particles of magnetic systems can
sometimes become unstable, thereby ceasing to exist. We used computer
simulations to investigate one of the simplest models of a quantum
magnetic system, the two dimensional spin-1/2 Heisenberg antiferromagnet
in an external magnetic field, and found that when the external field
becomes strong enough some of the elementary particles decay. Our
results strengthen previous findings made by others (Zhitomirsky &
Chernyshev) using analytical approximative methods. The model studied
here describes well the mother compound of the high-Tc superconducting
materials, as well as other magnetic materials.
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LR11507
Development of efficient photon-surface plasmon quantum coupling
Nanoscale quantum mechanical devices that are based on the interaction of
photons (light) with surface plasmons (collective electron oscillations)
promise to radically transform traditional information technologies. A major
roadblock has been the very low photon-to-surface plasmon transfer
efficiencies observed at the quantum level in experiments performed so far.
To address this issue, we have introduced the first quantum mechanical
description of efficient photon-surface plasmon coupling using a versatile
excitation setup. We discovered that remarkably high quantum efficiencies
can easily be reached for photon-to-surface plasmon transfer. We have also
established that the excited surface plasmons completely preserve important
quantum mechanical features of the original photons as they travel along
metal surfaces under realistic experimental conditions. Our results open up
a route toward the efficient manipulation of surface plasmons at the quantum
level in nanoplasmonic-based quantum information processing experiments.
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LS11087
Negative magnetization: an understanding at the atomic level using neutrons
Magnetization of a substance is a measure of the net magnetic moment per unit volume. It is well known that when an external magnetic field is applied on a ferromagnetic (or ferrimagnetic) substance, a net positive magnetization develops in it along the direction of the applied field. However, a negative magnetization may also appear. We have observed a negative magnetization in a Prussian blue-type molecular magnetic compound based on copper, manganese and iron. In this paper, the arrangement and orientation of copper, manganese and iron magnetic moments have been determined by analyzing the neutron scattering data using the Reverse Monte Carlo technique and the Rietveld refinement method. When the compound is cooled from its paramagnetic state, the iron and copper moments order at 22.5 K and their moments align parallel to each other in the direction of applied magnetic field giving a net positive magnetization. However, the manganese moments order
antiparallel to those of copper as well as iron at 13.5 K. Therefore, the net magnetization starts decreasing below 13.5 K and it becomes negative below 8.8 K when the manganese moment exceeds the sum of the copper and iron moments. Here, the magnetic anisotropy prevents the rotation of net magnetization below 8.8 K in the direction of magnetic field and causes a negative magnetization. The present understanding (at the atomic level) of the magnetization-polarity reversal would be very useful in designing magnetic memories since such a phenomenon offers two (positive and negative) magnetization states that are essential for a bi-stable magnetic memory. The bi-stable magnetization states may also be suitable for applications in thermo-magnetic switches and magneto-caloric devices.
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BQ10487
Nature possesses rare materials with negative refractive index!
In this paper, we show that negative index of refraction can be obtained in principally homogeneous magnetic semiconductor materials, e.g. Cr doped In2O3. These novel “natural” materials are very different from the existing metamaterials with negative refraction index, which are traditional inhomogeneous artificial structures made of metallic and dielectric elements. These traditional structures suffer from losses due to the inhomogeneities in the material, and the losses prevent usage of them in important exiting applications like “perfect lens” which, in principle, allows to reach optical resolution beyond the wavelength of light. This perfect lens could be used as part of a microscope to see tiny objects like a DNA molecule. The material which we present here, does not have these additional losses. Moreover, since our material is a magnetic semiconductor, it is much easier to fabricate compared to the composite materials, especially at high
frequencies. This unusual material presents the first of its kind in the THz regime. The applications of this novel THz material can be in personnel security screening, medical imaging, remote sensing, and biomedicine.
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BVR1101
Post Renaissance Mathematics Helps Computer Memory Device
A physicist at M. I. T. used a 500 year-old mathematical technique for
nding a solution for the motion of magnetic
`domain walls' in a material. These walls may be used in the computer
memory of the future and understanding their
motion is crucial to the operation of a device which shuttles these bits
around wires for reading and writing. The motion
of domain walls is often usually solved by running calculations over a
long time, but under some approximations, the
motion can be calculated by hand with the help of the of techniques
developed by Italian mathematician Scipione
Dal Ferro in 1517. This approach gave good agreement with experimental
data for the propagation of domain walls
in magnetic materials for which the approximations were relevant.
