Out-of-plane nesting driven spin spiral in ultrathin Fe/Cu(001) films

Epitaxial ultrathin Fe films on fcc Cu(001) exhibit a spin spiral (SS), in contrast to the ferromagnetism of bulk bcc Fe. We study the in-plane and out-of-plane Fermi surfaces (FSs) of the SS in 8 monolayer Fe/Cu(001) films using energy dependent soft x-ray momentum-resolved photoemission spectroscopy. We show that the SS originates in nested regions confined to out-of-plane FSs, which are drastically modified compared to in-plane FSs. From precise reciprocal space maps in successive zones, we obtain the associated real space compressive strain of 1.5+-0.5% along c-axis. An autocorrelation analysis quantifies the incommensurate ordering vector q=(2pi/a)(0,0,~0.86), favoring a SS and consistent with magneto-optic Kerr effect experiments. The results reveal the importance of in-plane and out-of-plane FS mapping for ultrathin films.Comment: 4 pages, 3 figure

Raman and fluorescence contributions to resonant inelastic soft x-ray scattering on LaAlO3_3/SrTiO3_3 heterostructures

We present a detailed study of the Ti 3$d$ carriers at the interface of LaAlO$_3$/SrTiO$_3$ heterostructures by high-resolution resonant inelastic soft x-ray scattering (RIXS), with special focus on the roles of overlayer thickness and oxygen vacancies. Our measurements show the existence of interfacial Ti 3$d$ electrons already below the critical thickness for conductivity and an increase of the total interface charge up to a LaAlO$_3$ overlayer thickness of 6 unit cells before it levels out. By comparing stoichiometric and oxygen deficient samples we observe strong Ti 3$d$ charge carrier doping by oxygen vacancies. The RIXS data combined with photoelectron spectroscopy and transport measurements indicate the simultaneous presence of localized and itinerant charge carriers. However, it is demonstrated that the relative amount of localized and itinerant Ti $3d$ electrons in the ground state cannot be deduced from the relative intensities of the Raman and fluorescence peaks in excitation energy dependent RIXS measurements, in contrast to previous interpretations. Rather, we attribute the observation of either the Raman or the fluorescence signal to the spatial extension of the intermediate state reached in the RIXS excitation process.Comment: 9 pages, 6 figure

Tracking of Normal and Malignant Progenitor Cell Cycle Transit in a Defined Niche.

While implicated in therapeutic resistance, malignant progenitor cell cycle kinetics have been difficult to quantify in real-time. We developed an efficient lentiviral bicistronic fluorescent, ubiquitination-based cell cycle indicator reporter (Fucci2BL) to image live single progenitors on a defined niche coupled with cell cycle gene expression analysis. We have identified key differences in cell cycle regulatory gene expression and transit times between normal and chronic myeloid leukemia progenitors that may inform cancer stem cell eradication strategies

Three-dimensional bulk band dispersion in polar BiTeI with giant Rashba-type spin splitting

In layered polar semiconductor BiTeI, giant Rashba-type spin-split band dispersions show up due to the crystal structure asymmetry and the strong spin-orbit interaction. Here we investigate the 3-dimensional (3D) bulk band structures of BiTeI using the bulk-sensitive $h\nu$-dependent soft x-ray angle resolved photoemission spectroscopy (SX-ARPES). The obtained band structure is shown to be well reproducible by the first-principles calculations, with huge spin splittings of ${\sim}300$ meV at the conduction-band-minimum and valence-band-maximum located in the $k_z=\pi/c$ plane. It provides the first direct experimental evidence of the 3D Rashba-type spin splitting in a bulk compound.Comment: 9 pages, 4 figure

Size-dependent permittivity and intrinsic optical anisotropy of nanometric gold thin films: A density functional theory study

Physical properties of materials are known to be different from the bulk at the nanometer scale. In this context, the dependence of optical properties of nanometric gold thin films with respect to film thickness is studied using density functional theory (DFT). We find that the in-plane plasma frequency of the gold thin film decreases with decreasing thickness and that the optical permittivity tensor is highly anisotropic as well as thickness dependent. Quantitative knowledge of planar metal film permittivity's thickness dependence can improve the accuracy and reliability of the designs of plasmonic devices and electromagnetic metamaterials. The strong anisotropy observed may become an alternative method of realizing indefinite media. © 2013 Optical Society of America

Moving Beyond Dichotomies: How the Intersection of Race, Class and Place Impacts High School Graduation Rates for African American Students

Over thirty years ago, William Julius Wilson declared that class trumped race as the more significant determinant of social mobility and economic opportunity. Despite the acclaim and scrutiny for Wilson\u27s work, the United States has grown increasingly divided by intersecting factors of race, class and other demographic factors such as place (Massey, 2007). These divisions are especially evident in the public education system. We analyze how race, class and place interact to predict high school graduation rates in a national sample of schools and students. Results confirm that a singular focus on race, class, or locale is insufficient to explain high school graduation rates. However, a more contextualized focus on the interactions between multiple determinants of inequality (e.g. race, class and place) can yield a more nuanced understanding of the indicators driving educational inequalities. Scholars and practitioners need to focus on the manner in which multiple positionalities influence the academic achievement of African American children and young adults

Suzaku Observation of Two Ultraluminous X-Ray Sources in NGC 1313

Two ultraluminous X-ray sources (ULXs) in the nearby Sb galaxy NGC 1313, named X-1 and X-2, were observed with Suzaku on 2005 September 15. During the observation for a net exposure of 28~ks (but over a gross time span of 90~ks), both objects varied in intensity by about 50~%. The 0.4--10 keV X-ray luminosity of X-1 and X-2 was measured as $2.5 \times 10^{40}~{\rm erg~s^{-1}}$ and $5.8 \times 10^{39}~{\rm erg~s^{-1}}$, respectively, with the former the highest ever reported for this ULX. The spectrum of X-1 can be explained by a sum of a strong and variable power-law component with a high energy cutoff, and a stable multicolor blackbody with an innermost disk temperature of $\sim 0.2$ keV. These results suggest that X-1 was in a ``very high'' state, where the disk emission is strongly Comptonized. The absorber within NGC 1313 toward X-1 is suggested to have a subsolar oxygen abundance. The spectrum of X-2 is best represented, in its fainter phase, by a multicolor blackbody model with the innermost disk temperature of 1.2--1.3 keV, and becomes flatter as the source becomes brighter. Hence X-2 is interpreted to be in a slim-disk state. These results suggest that the two ULXs have black hole masses of a few tens to a few hundreds solar masses.Comment: accepted for publication in PAS