Relative replication capacity of phenotypic SIV variants during primary infections differs with route of inoculation

BACKGROUND: Previous studies of human and simian immunodeficiency virus (HIV and SIV) have demonstrated that adaptive mutations selected during the course of infection alter viral replicative fitness, persistence, and pathogenicity. What is unclear from those studies is the impact of transmission on the replication and pathogenicity of the founding virus population. Using the SIV-macaque model, we examined whether the route of infection would affect the establishment and replication of two SIVmne variants of distinct in vitro and in vivo biological characteristics. For these studies, we performed dual-virus inoculations of pig-tailed macaques via intrarectal or intravenous routes with SIVmneCl8, a miminally pathogenic virus, and SIVmne027, a highly pathogenic variant that replicates more robustly in CD4(+ )T cells. RESULTS: The data demonstrate that SIVmne027 is the dominant virus regardless of the route of infection, indicating that the capacity to replicate efficiently in CD4(+ )T cells is important for fitness. Interestingly, in comparison to intravenous co-infection, intrarectal inoculation enabled greater relative replication of the less pathogenic virus, SIVmneCl8. Moreover, a higher level of SIVmneCl8 replication during primary infection of the intrarectally inoculated macaques was associated with lower overall plasma viral load and slower decline in CD4(+ )T cells, even though SIVmne027 eventually became the dominant virus. CONCLUSIONS: These results suggest that the capacity to replicate in CD4(+ )T cells is a significant determinant of SIV fitness and pathogenicity. Furthermore, the data also suggest that mucosal transmission may support early replication of phenotypically diverse variants, while slowing the rate of CD4(+ )T cell decline during the initial stages of infection

Phase Diagram of Pressure-Induced Superconductivity in EuFe2As2 Probed by High-Pressure Resistivity up to 3.2 GPa

We have constructed a pressure$-$temperature ($P-T$) phase diagram of $P$-induced superconductivity in EuFe$_2$As$_2$ single crystals, via resistivity ($\rho$) measurements up to 3.2 GPa. As hydrostatic pressure is applied, an antiferromagnetic (AF) transition attributed to the FeAs layers at $T_\mathrm{0}$ shifts to lower temperatures, and the corresponding resistive anomaly becomes undetectable for $P$ $\ge$ 2.5 GPa. This suggests that the critical pressure $P_\mathrm{c}$ where $T_\mathrm{0}$ becomes zero is about 2.5 GPa. We have found that the AF order of the Eu$^{2+}$ moments survives up to 3.2 GPa without significant changes in the AF ordering temperature $T_\mathrm{N}$. The superconducting (SC) ground state with a sharp transition to zero resistivity at $T_\mathrm{c}$ $\sim$ 30 K, indicative of bulk superconductivity, emerges in a pressure range from $P_\mathrm{c}$ $\sim$ 2.5 GPa to $\sim$ 3.0 GPa. At pressures close to but outside the SC phase, the $\rho(T)$ curve shows a partial SC transition (i.e., zero resistivity is not attained) followed by a reentrant-like hump at approximately $T_\mathrm{N}$ with decreasing temperature. When nonhydrostatic pressure with a uniaxial-like strain component is applied using a solid pressure medium, the partial superconductivity is continuously observed in a wide pressure range from 1.1 GPa to 3.2 GPa.Comment: 7 pages, 6 figures, accepted for publication in Physical Review B, selected as "Editors' Suggestion

Detection of the interfacial exchange field at a ferromagnetic insulator-nonmagnetic metal interface with pure spin currents

At the interface between a nonmagnetic metal (NM) and a ferromagnetic insulator (FI) spin current can interact with the magnetization, leading to a modulation of the spin current. The interfacial exchange field at these FI-NM interfaces can be probed by placing the interface in contact with the spin transport channel of a lateral spin valve (LSV) device and observing additional spin relaxation processes. We study interfacial exchange field in lateral spin valve devices where Cu spin transport channel is in proximity with ferromagnetic insulator EuS (EuS-LSV) and yttrium iron garnet Y$_3$Fe$_5$O$_{12}$ (YIG-LSV). The spin signals were compared with reference lateral spin valve devices fabricated on nonmagnetic Si/SiO$_2$ substrate with MgO or AlO$_x$ capping. The nonlocal spin valve signal is about 4 and 6 times lower in the EuS-LSV and YIG-LSV, respectively. The suppression in the spin signal has been attributed to enhanced surface spin-flip probability at the Cu-EuS (or Cu-YIG) interface due to interfacial spin-orbit field. Besides spin signal suppression we also found widely observed low temperature peak in the spin signal at $T \sim$30 K is shifted to higher temperature in the case of devices in contact with EuS or YIG. Temperature dependence of spin signal for different injector-detector distances reveal fluctuating exchange field at these interfaces cause additional spin decoherence which limit spin relaxation time in addition to conventional sources of spin relaxation. Our results show that temperature dependent measurement with pure spin current can be used to probe interfacial exchange field at the ferromagnetic insulator-nonmagnetic metal interface.Comment: 10 pages, 3 figures, accepted in Physical Review

Quasi-Two-Dimensional Fermi Surfaces and Coherent Interlayer Transport in KFe2_2As2_2

We report the results of the angular-dependent magnetoresistance oscillations (AMROs), which can determine the shape of bulk Fermi surfaces in quasi-two-dimensional (Q2D) systems, in a highly hole-doped Fe-based superconductor KFe$_2$As$_2$ with $T_c \approx$ 3.7 K. From the AMROs, we determined the two Q2D FSs with rounded-square cross sections, corresponding to 12% and 17% of the first Brillouin zone. The rounded-squared shape of the FS cross section is also confirmed by the analyses of the interlayer transport under in-plane fields. From the obtained FS shape, we infer the character of the 3d orbitals that contribute to the FSs.Comment: 4 pages, 4 figures, accepted in Phys. Rev. Let

High-Pressure Electrical Resistivity Measurements of EuFe2As2 Single Crystals

High-pressure electrical resistivity measurements up to 3.0GPa have been performed on EuFe2As2 single crystals with residual resistivity ratios RRR=7 and 15. At ambient pressure, a magnetic / structural transition related to FeAs-layers is observed at T0 =190K and 194K for samples with RRR=7 and 15, respectively. Application of hydrostatic pressure suppresses T0, and then induces similar superconducting behavior in the samples with different RRR values. However, the critical pressure 2.7GPa, where T0=0, for the samples with RRR=15 is slightly but distinctly larger than 2.5GPa for the samples with RRR=7.Comment: To be published in J. Phys.: Conf. Se

Quantum oscillations in a centrosymmetric skyrmion-hosting magnet GdRu2Si2

We have performed magnetic torque and resistivity measurements on a centrosymmetric skyrmion-host GdRu2Si2, in which the dominant magnetic interaction leading to skyrmion formation is under debate. We observe both the de Haas-van Alphen and Shubnikov-de Haas oscillations in the forced ferromagnetic phase. The angular dependence of the quantum oscillation frequencies can be reproduced by the ab-initio calculation. The de Haas-van Alphen oscillation is also observed in the double-Q phase with a different frequency to that in the forced ferromagnetic phase, indicating a Fermi surface reconstruction due to the coupling between localized spins and conduction electrons. Based on these experimental findings, the magnetic interactions in this system are discussed.Comment: 11 pages, 8 figure

The Competition between Staggered Field and Antiferromagnetic Interactions in Cugeo3:Fe

The EPR spectra along different crystallographic axes for single crystals of CuGeO3 containing 1% of Fe impurity have been studied in the frequency range 60-360 GHz at temperatures 0.5-30 K. The analysis based on the Oshikawa-Affleck (OA) theory suggests that the temperature dependences of the line width and g-factor are formed as a result of the competition between interchain antiferromagnetic interactions and staggered Zeeman energy. It is found that staggered magnetic moments in CuGeO3:Fe are located predominantly along b axis.Comment: 9 pages, 4 figures; submitted to QSS04 symposiu