Molecular-beam epitaxy of (Zn,Mn)Se on Si(100)

We have investigated the growth by molecular-beam epitaxy of the II-VI diluted magnetic semiconductor (Zn,Mn)Se on As-passivated Si(100) substrates. The growth start has been optimized by using low-temperature epitaxy. Surface properties were assessed by Nomarski and scanning electron microscopy. Optical properties of (Zn,Mn)Se have been studied by photoluminescence and a giant Zeeman splitting of up to 30 meV has been observed. Our observations indicate a high crystalline quality of the epitaxial films.Comment: To be published in Applied Physics Letter

Tunneling magnetoresistance in devices based on epitaxial NiMnSb with uniaxial anisotropy

We demonstrate tunnel magnetoresistance (TMR) junctions based on a tri layer system consisting of an epitaxial NiMnSb, aluminum oxide and CoFe tri layer. The junctions show a tunnelling magnetoresistance of Delta R/R of 8.7% at room temperature which increases to 14.7% at 4.2K. The layers show clear separate switching and a small ferromagnetic coupling. A uniaxial in plane anisotropy in the NiMnSb layer leads to different switching characteristics depending on the direction in which the magnetic field is applied, an effect which can be used for sensor applications.Comment: 8 pages, 3 figures, submitted to Appl. Phys. Let

Exploiting Locally Imposed Anisotropies in (Ga,Mn)As: a Non-volatile Memory Device

Progress in (Ga,Mn)As lithography has recently allowed us to realize structures where unique magnetic anisotropy properties can be imposed locally in various regions of a given device. We make use of this technology to fabricate a device in which we study transport through a constriction separating two regions whose magnetization direction differs by 90 degrees. We find that the resistance of the constriction depends on the flow of the magnetic field lines in the constriction region and demonstrate that such a structure constitutes a non-volatile memory device

Very large magnetoresistance in lateral ferromagnetic (Ga,Mn)As wires with nanoconstrictions

We have fabricated (Ga,Mn)As nanostructures in which domain walls can be pinned by sub-10 nm constrictions. Controlled by shape anisotropy, we can switch the regions on either side of the constriction to either parallel or antiparallel magnetization. All samples exhibit a positive magnetoresistance, consistent with domain-wall trapping. For metallic samples we find a magnetoresistance up to 8%, which can be understood from spin accumulation. In samples where, due to depletion at the constriction, a tunnel barrier is formed, we observe a magnetoresistance of up to 2000 %.Comment: 4 pages, 3 figures, submited to Phys. Rev. Let

Gapless phases of color-superconducting matter

We discuss gapless color superconductivity for neutral quark matter in beta equilibrium at zero as well as at nonzero temperature. Basic properties of gapless superconductors are reviewed. The current progress and the remaining problems in the understanding of the phase diagram of strange quark matter are discussed.Comment: 8 pages, 2 figures. Plenary talk at Strangeness in Quark Matter 2004 (SQM2004), Cape Town, South Africa, 15-20 September 2004. Minor correction

Two lectures on color superconductivity

The first lecture provides an introduction to the physics of color superconductivity in cold dense quark matter. The main color superconducting phases are briefly described and their properties are listed. The second lecture covers recent developments in studies of color superconducting phases in neutral and beta-equilibrated matter. The properties of gapless color superconducting phases are discussed.Comment: 56 pages, 9 figures. Minor corrections and references added. Lectures delivered at the IARD 2004 conference, Saas Fee, Switzerland, June 12 - 19, 2004, and at the Helmholtz International Summer School and Workshop on Hot points in Astrophysics and Cosmology, JINR, Dubna, Russia, August 2 - 13, 200

A quantitative polymerase chain reaction-enzyme immunoassay for accurate measurements of human papillomavirus type 16 DNA levels in cervical scrapings

A quantitative polymerase chain reaction-enzyme immunoassay (Q-PCR-EIA) was developed to measure the amount of human papillomavirus (HPV) 16 DNA per genome equivalent in cervical scrapings. The quantitative approach was based on a combined competitive PCR for both HPV 16, using the general primer GP5+/6+ PCR, and β-globin DNA. The two competitive PCRs involve co-amplification of target sequences and exogenously added DNA constructs carrying a rearranged 30 bp sequence in the probe-binding region. The accuracy of quantification by combining the two competitive PCR assays was validated on mixtures of HPV 16 containing cervical cancer cells of CaSki and SiHa cell lines. Comparison of this fully quantitative PCR assay with two semi-quantitative HPV PCR assays on a series of crude cell suspensions from HPV 16 containing cervical scrapings revealed remarkable differences in the calculated relative HPV load between samples. We found evidence that correction for both intertube variations in PCR efficiency and number of input cells/integrity of DNA significantly influence the outcome of studies on viral DNA load in crude cell suspensions of cervical scrapings. Therefore, accurate measurements on viral DNA load in cervical scrapings require corrections for these phenomena, which can be achieved by application of this fully quantitative approach. © 1999 Cancer Research Campaig