Impact of future HERA data on the determination of proton parton distribution functions using the ZEUS QCD fit

The high precision and large kinematic coverage of the data from the HERA-I running period (1994-2000) have already allowed precise extractions of proton parton distribution functions (PDFs). The HERA-II running program is now underway and is expected to provide a substantial increase in the luminosity collected at HERA. In this paper, a study is presented which investigates the potential impact of future data from HERA on the proton PDF uncertainties, within the currently planned running scenario. In addition, the effect of a possible future measurement of the longitudinal structure function, FL, on the gluon distribution is investigated.Comment: 5 pages, 2 figures, in proceedings of the XIII International Workshop on Deep Inelastic Scattering - DIS 2005, Madison, Wisconsin, 200

Electrical transport properties of nanostructured ferromagnetic perovskite oxides La_0.67Ca_0.33MnO_3 and La_0.5Sr_0.5CoO_3 at low temperatures (5 K > T >0.3 K) and high magnetic field

We report a comprehensive study of the electrical and magneto-transport properties of nanocrystals of La_0.67Ca_0.33MnO_3 (LCMO) (with size down to 15 nm) and La_0.5Sr_0.5CoO_3 (LSCO) (with size down to 35 nm) in the temperature range 0.3 K to 5 K and magnetic fields upto 14 T. The transport, magnetotransport and non-linear conduction (I-V curves) were analysed using the concept of Spin Polarized Tunnelling in the presence of Coulomb blockade. The activation energy of transport, \Delta, was used to estimate the tunnelling distances and the inverse decay length of the tunnelling wave function (\chi) and the height of the tunnelling barrier (\Phi_B). The magnetotransport data were used to find out the magnetic field dependences of these tunnelling parameters. The data taken over a large magnetic field range allowed us to separate out the MR contributions at low temperatures arising from tunnelling into two distinct contributions. In LCMO, at low magnetic field, the transport and the MR are dominated by the spin polarization, while at higher magnetic field the MR arises from the lowering of the tunnel barrier by the magnetic field leading to an MR that does not saturate even at 14 T. In contrast, in LSCO, which does not have substantial spin polarization, the first contribution at low field is absent, while the second contribution related to the barrier height persists. The idea of inter-grain tunnelling has been validated by direct measurements of the non-linear I-V data in this temperature range and the I-V data was found to be strongly dependent on magnetic field. We made the important observation that a gap like feature (with magnitude ~ E_C, the Coulomb charging energy) shows up in the conductance g(V) at low bias for the systems with smallest nanocrystal size at lowest temperatures (T < 0.7 K). The gap closes as the magnetic field and the temperature are increased.Comment: 13 figure

Aspects of Duality in Nodal Liquids

Starting from a microscopic t-J like model and a SU(2) spin-charge separation ansatz, a relativistic continuum gauge lagrangian is obtained in the vicinity of a nodal point of the Fermi surface. The excitations in the pseudogap phase are described by topological excitations in the dual model which has a Z_2 global symmetry due to the effect of instantons. Confinement of spinon and holons emerge from this picture. The adjoint and fundamental strings are associated with stripes. As the spin gap decreases a local Z_2 symmetry emerges.Comment: 15 pages revtex, no figure

Spin rings in bi-stable planar semiconductor microcavities

A unique feature of exciton-polaritons, inherited from their mixed light-matter origin, is the strongly spin-dependent polariton-polariton interaction, which has been predicted to result in the formation of spin rings in real space [Shelykh et al., Phys. Rev. Lett. 100, 116401 (2008)]. Here we experimentally demonstrate the spin bi-stability of exciton-polaritons in an InGaAs-based semiconductor microcavity under resonant optical pumping. We observe the formation of spin rings whose size can be finely controlled in a spatial scale down to the micrometer range, much smaller than the spot size. We additionally evaluate the sign and magnitude of the antiparallel polariton spin interaction constant.Comment: 5 pages, 4 figure

Unconventional magnetism in multivalent charge-ordered YbPtGe2_2 probed by 195^{195}Pt- and 171^{171}Yb-NMR

Detailed $^{195}$Pt- and $^{171}$Yb nuclear magnetic resonance (NMR) studies on the heterogeneous mixed valence system YbPtGe$_2$ are reported. The temperature dependence of the $^{195}$Pt-NMR shift $^{195}K(T)$ indicates the opening of an unusual magnetic gap below 200\,K. $^{195}K(T)$ was analyzed by a thermal activation model which yields an isotropic gap $\Delta/k_B \approx 200$\,K. In contrast, the spin-lattice relaxation rate $^{195}$($1/T_1$) does not provide evidence for the gap. Therefore, an intermediate-valence picture is proposed while a Kondo-insulator scenario can be excluded. Moreover, $^{195}$($1/T_1$) follows a simple metallic behavior, similar to the reference compound YPtGe$_2$. A well resolved NMR line with small shift is assigned to divalent $^{171}$Yb. This finding supports the proposed model with two sub-sets of Yb species (di- and trivalent) located on the Yb2 and Yb1 site of the YbPtGe$_2$ lattice.Comment: Submitted in Physical Review B (Rapid Communication