Scavenging of atmospheric ions and aerosols by drifting snow in Antarctica

Measurements of the small,intermediate, and large ion concentrations and the airearth current density along with simultaneous measurements of the concentration and size-distribution of aerosol particles in the size ranges 4.4 to 163 nm and 0.5 to 20 micrometer diameters are reported for a drifting snow period after the occurrence of a blizzard at a coastal station, Maitri, Antarctica. Ion concentrations of all categories and the airearth current simultaneously decrease by approximately an order of magnitude as the wind speed increases from 5 to 10 meter per sec. The rate of decrease is the highest for large ions, lowest for small ions and in between the two for intermediate ions. Total aerosol number concentration decreases in the 4.4 to 163 nm size range but increases in 0.5 to 20 micrmetr size range with wind speed. Size distribution of the nanometer particles show a dominant maximum at 30 nm diameter throughout the period of observations and the height of the maximum decreases with wind speed. However, larger particles show a maximum at 0.7 micrometer diameter but the height of the maximum increases with increasing wind speed. The results are explained in terms of scavenging of atmospheric ions and aerosols by the drifting snow particles.Comment: 12 pages and 5figur

Super-Poissonian shot noise of squeezed-magnon mediated spin transport

The magnetization of a ferromagnet (F) driven out of equilibrium injects pure spin current into an adjacent conductor (N). Such F$|$N bilayers have become basic building blocks in a wide variety of spin based devices. We evaluate the shot noise of the spin current traversing the F$|$N interface when F is subjected to a coherent microwave drive. We find that the noise spectrum is frequency independent up to the drive frequency, and increases linearly with frequency thereafter. The low frequency noise indicates super-Poissonian spin transfer, which results from quasi-particles with effective spin $\hbar^* = \hbar (1 + \delta)$. For typical ferromagnetic thin films, $\delta \sim 1$ is related to the dipolar interaction-mediated squeezing of F eigenmodes.Comment: 4 pages, 2 figure

Spin pumping and shot noise in ferrimagnets: bridging ferro- and antiferromagnets

A combination of novel technological and fundamental physics prospects has sparked a huge interest in pure spin transport in magnets, starting with ferromagnets and spreading to antiferro- and ferrimagnets. We present a theoretical study of spin transport across a ferrimagnet$|$non-magnetic conductor interface, when a magnetic eigenmode is driven into a coherent state. The obtained spin current expression includes intra- as well as cross-sublattice terms, both of which are essential for a quantitative understanding of spin-pumping. The dc current is found to be sensitive to the asymmetry in interfacial coupling between the two sublattice magnetizations and the mobile electrons, especially for antiferromagnets. We further find that the concomitant shot noise provides a useful tool for probing the quasiparticle spin and interfacial coupling.Comment: 4 pages + supplementary materia

Magnon-mediated spin current noise in ferromagnet∣|non-magnetic conductor hybrids

The quantum excitations of the collective magnetization dynamics in a ferromagnet (F) - magnons - enable spin transport without an associated charge current. This pure spin current can be transferred to electrons in an adjacent non-magnetic conductor (N). We evaluate the finite temperature noise of the magnon-mediated spin current injected into N by an adjacent F driven by a coherent microwave field. We find that the dipolar interaction leads to squeezing of the magnon modes giving them wavevector dependent non-integral spin, which directly manifests itself in the shot noise. For temperatures higher than the magnon gap, the thermal noise is dominated by large wavevector magnons which exhibit negligible squeezing. The noise spectrum is white up to the frequency corresponding to the maximum of the temperature or the magnon gap. At larger frequencies, the noise is dominated by vacuum fluctuations. The shot noise is found to be much larger than its thermal counterpart over a broad temperature range, making the former easier to be measured experimentally

Using superconductivity to control magnetism: a facet of superconducting spintronics

Magnets are used in electronics to store and read information. A magnetic moment is rotated to a desired direction, so that information can later be retrieved by reading this orientation. Controlling the moment via electric currents causes resistive losses and heating, a major bottleneck in advancing computing technologies. Superconducting spintronics can resolve this using the unique features of superconductors.Comment: Feature in Europhysics News (4 pages

Die Discrete Mode Matching Methode für konforme mehrlagige Strukturen mit anisotropen Substraten

The discrete mode matching method has been proven to be an efficient numerical method to analyze multilayered structures with thin dielectric layers for microwave and optical technologies. The main contribution of this thesis is to extend the method to structures which consist of anisotropic or isotropic, homogeneous or inhomogeneous dielectric layers, or metamaterials. The mathematical formulation is well suited for the analysis of conformal structures (e.g., arbitrarily shaped waveguides and antennas).Discrete Mode Matching ist eine bewährte Methode zur Analyse von mehrlagigen Strukturen mit dünnen dielektrischen Lagen, wie sie in der Mikrowellentechnik und Optik eingesetzt werden. Der Hauptbeitrag dieser Dissertation ist die Erweiterung dieser Methode auf Strukturen, die aus anisotropen oder isotropen, homogenen oder inhomogenen dielektrischen Lagen sowie Metamaterialien bestehen. Die mathematische Formulierung ist für die Analyse von Strukturen mit beliebiger Form (z. B. Antennen) geeignet

Self-Making through Self-Writing: Non-Sovereign Agency in Women's Memoirs from the Naxalite Movement

Women were active participants in the Naxalite movement of the 1960s and 1970s in India but were made invisible in the mainstream historiography of the movement. However, memoirs and autobiographies of women Naxalites bring out their experiences of participation in the movement. This paper engages with the memoirs of two of them, K. Ajitha and Krishna Bandyopadhyay, and argues that these women demonstrate a non-sovereign agency in self-making through these autobiographical narratives