High spin polarization and the origin of unique ferromagnetic ground state in CuFeSb

CuFeSb is isostructural to the ferro-pnictide and chalcogenide superconductors and it is one of the few materials in the family that are known to stabilize in a ferromagnetic ground state. Majority of the members of this family are either superconductors or antiferromagnets. Therefore, CuFeSb may be used as an ideal source of spin polarized current in spin-transport devices involving pnictide and the chalcogenide superconductors. However, for that the Fermi surface of CuFeSb needs to be sufficiently spin polarized. In this paper we report direct measurement of transport spin polarization in CuFeSb by spin-resolved Andreev reflection spectroscopy. From a number of measurements using multiple superconducting tips we found that the intrinsic transport spin polarization in CuFeSb is high ($\sim$ 47\%). In order to understand the unique ground state of CuFeSb and the origin of large spin polarization at the Fermi level, we have evaluated the spin-polarized band structure of CuFeSb through first principles calculations. Apart from supporting the observed 47\% transport spin polarization, such calculations also indicate that the Sb-Fe-Sb angles and the height of Sb from the Fe plane is strikingly different for CuFeSb than the equivalent parameters in other members of the same family thereby explaining the origin of the unique ground state of CuFeSb.Comment: 6 pages, 4 figure

Optical properties of atmospheric aerosols over the Arabian Sea and Indian Ocean: North-South contrast across the ITCZ

Extensive estimates of aerosol spectral optical depths are made over the Arabian Sea and south-western Indian Ocean, using a 10-channel multi-wavelength solar radiometer (MWR) and a 4- channel hand held EKO sun-photometer (ESP) on-board the cruise # 133 of ORV Sagar Kanya during the First Field Phase (FFP- 98) of the Indian Ocean experiment (INDOEX) in February and March 1998. High values of optical depths, particularly in the visible wavelengths, are encountered in the coastal areas, with a gradual increase from Goa to Male, The optical depths decrease sharply as the ship moves out to the south western Indian Ocean across the equator; the effect is more significant at shorter wavelengths. Over the pris-tine environment south of the ITCZ, extremely low optical depths appear at the visible wavelengths, while at the NIR wavelengths, the optical depths remain nearly the same as on the northern side. On the return Ieg, again higher optical depths are encountered north of the ITCZ with those at the visible wavelengths sharply increased. Over the north-western Arabian Sea, higher optical depthvalues occur farther away from the coast, suggesting additional input of aerosols over mid ocean, possibly transported by various wind trajectories from the west Asian deserts. Comparing air trajectories both at the surface and 850 h Pa reveals that in addition to those advected from continental India, winds transporting aerosols from various north/west Asian regions contribute significantly to the aerosol optical depths over the Arabian Sea

Quasi-deterministic Localization of Er Emitters in Thin Film TiO2_2 through Submicron-scale Crystalline Phase Control

With their shielded 4f orbitals, rare-earth ions (REIs) offer optical and electron spin transitions with good coherence properties even when embedded in a host crystal matrix, highlighting their utility as promising quantum emitters and memories for quantum information processing. Among REIs, trivalent erbium (Er$^{3+}$) uniquely has an optical transition in the telecom C-band, ideal for transmission over optical fibers, and making it well-suited for applications in quantum communication. The deployment of Er$^{3+}$ emitters into a thin film TiO$_2$ platform has been a promising step towards scalable integration; however, like many solid-state systems, the deterministic spatial placement of quantum emitters remains an open challenge. We investigate laser annealing as a means to locally tune the optical resonance of Er$^{3+}$ emitters in TiO$_2$ thin films on Si. Using both nanoscale X-ray diffraction measurements and cryogenic photoluminescence spectroscopy, we show that tightly focused below-gap laser annealing can induce anatase to rutile phase transitions in a nearly diffraction-limited area of the films and improve local crystallinity through grain growth. As a percentage of the Er:TiO$_2$ is converted to rutile, the Er$^{3+}$ optical transition blueshifts by 13 nm. We explore the effects of changing laser annealing time and show that the amount of optically active Er:rutile increases linearly with laser power. We additionally demonstrate local phase conversion on microfabricated Si structures, which holds significance for quantum photonics.Comment: 7 pages, 4 figure

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

On estimating the atomic hydrogen column density from the HI 21 cm emission spectra

The 21 cm hyperfine transition of the atomic hydrogen (HI) in ground state is a powerful probe of the neutral gas content of the Universe. This radio frequency transition has been used routinely for decades to observe, both in emission and absorption, HI in the Galactic interstellar medium as well as in extragalactic sources. In general, however, it is not trivial to derive the physically relevant parameters like temperature, density, or column density from these observations. Here, we have considered the issue of column density estimation from the HI 21 cm emission spectrum for sightlines with a non-negligible optical depth and a mix of gas at different temperatures. The complicated radiative transfer and a lack of knowledge about the relative position of gas clouds along the sightline often make it impossible to uniquely separate the components, and hinders reliable estimation of column densities in such cases. Based on the observed correlation between the 21 cmbrightness temperature and optical depth, we propose a method to get an unbiased estimate of the HI column density using only the 21 cm emission spectrum. This formalism is further used for a large sample to study the spin temperature of the neutral interstellar medium

A study of Kepler supernova remnant: angular power spectrum estimation from radio frequency data

Supernova remnants (SNRs) have a variety of overall morphology as well as rich structures over a wide range of scales. Quantitative study of these structures can potentially reveal fluctuations of density and magnetic field originating from the interaction with ambient medium and turbulence in the expanding ejecta. We have used 1.5 GHz (L band) and 5 GHz (C band) VLA data to estimate the angular power spectrum C-l of the synchrotron emission fluctuations of the Kepler SNR. This is done using the novel, visibility-based, Tapered Gridded Estimator of C-l. We have found that, for l = (1.9-6.9) x 10(4), the power spectrum is a broken power law with a break at l = 3.3 x 10(4), and power-law index of -2.84 +/- 0.07 and -4.39 +/- 0.04 before and after the break, respectively. The slope -2.84 is consistent with 2D Kolmogorov turbulence and earlier measurements for the Tycho SNR. We interpret the break to be related to the shell thickness of the SNR (0.35 pc) which approximately matches l = 3.3 x 10(4) (i.e. 0.48 pc). However, for l > 6.9 x 10(4), the estimated C-l of L band is likely to have dominant contribution from the foregrounds while for C band the power-law slope -3.07 +/- 0.02 is roughly consistent with 3D Kolmogorov turbulence like that observed at large l for Cas A and Crab SNRs

Aerosol size characteristics over the Arabian Sea and Indian Ocean: extensive sub-micron aerosol loading in the Northern Hemisphere

Aerosol optical depth (AOD) measurements in the spectral range 0.3–1.6 mm have been carried out using a multi-channel solar radiometer onboard ORV Sagar Kanya to understand the interaction between continental and marine aerosols. Experiments have been carried out under clear sky conditions for 22 days during 20 January–12 March 1999 covering the latitude belt between 17°N and 20°S, and longitude belt between 71°E and 59°E, over Indian Ocean and Arabian Sea as part of INDOEX IFP-99. Results show larger particle abundance, close to the Indian coast during forward leg compared to that of return leg of the cruise. AODs, in general, exhibit larger values north of ITCZ compared to that of south of ITCZ. The spatial distribution of AOD at 0.502 mm shows greater values north of ITCZ with significant latitudinal gradient compared to that of south of ITCZ. Aerosol size spectrum, derived from spectral AODs, shows monomodal distribution for both pristine oceanic environment (south of ITCZ) and for polluted environment (north of ITCZ)