Quantum Melting of Charge Order due to Frustration in Two-Dimensional Quarter-Filled Systems

The effect of geometrical frustration in a two-dimensional 1/4-filled strongly correlated electron system is studied theoretically, motivated by layered organic molecular crystals. An extended Hubbard model on the square lattice is considered, with competing nearest neighbor Coulomb interaction, V, and that of next-nearest neighbor along one of the diagonals, V', which favor different charge ordered states. Based on exact diagonalization calculations, we find a metallic phase stabilized over a broad window at V' ~ V even for large Coulomb repulsion strengths as a result of frustrating the charge ordered states. Slightly modifying the lattice geometry relevant to the actual organic compounds does not alter the results, suggesting that this `quantum melting' of charge order is a robust feature of frustrated strongly correlated 1/4-filled systems.Comment: 5 pages, 4 figures, to be published in Phys. Rev.

Quarter-filled spin density wave states with long-range Coulomb interaction

Spin density wave (SDW) states at quarter-filling, which coexist with charge density wave (CDW) states, have been examined where the critical temperature is calculated for an extended Hubbard model with long range repulsive interactions. Within the mean-field theory, it is shown that the first order transition occurs with decreasing temperature for interactions located around the boundary between SDW state and CDW state.Comment: 4 pages, 5 figures, Proceedings of CREST International Workshop (Nagoya, Japan, 24-26 January, 2000), submitted to J. Phys. Chem. Solid

Collisional Dynamics of Half-Quantum Vortices in a Spinor Bose-Einstein Condensate

We present an experimental study on the interaction and dynamics of half-quantum vortices (HQVs) in an antiferromagnetic spinor Bose-Einstein condensate. By exploiting the orbit motion of a vortex dipole in a trapped condensate, we perform a collision experiment of two HQV pairs, and observe that the scattering motions of the HQVs is consistent with the short-range vortex interaction that arises from nonsingular magnetized vortex cores. We also investigate the relaxation dynamics of turbulent condensates containing many HQVs, and demonstrate that spin wave excitations are generated by the collisional motions of the HQVs. The short-range vortex interaction and the HQV-magnon coupling represent two characteristics of the HQV dynamics in the spinor superfluid.Comment: 7 pages, 6 figure

Detection of X-ray periodicity from a new eclipsing polar candidate XGPS-I J183251-100106

We report the results from a detailed analysis of an archival XMM-Newton observation of the X-ray source XGPS-I J183251-100106, which has been suggested as a promising magnetic cataclysmic variable candidate based on its optical properties. A single periodic signal of 1.5 hrs is detected from all EPIC cameras on board XMM-Newton. The phase-averaged X-ray spectrum can be well-modeled with a thermal bremsstrahlung of a temperature kT~50 keV. Both X-ray spectral and temporal behavior of this system suggest it as a eclipsing cataclysmic variable of AM Herculis (or polar) type.Comment: 15 pages, 6 figures, accepted for publication in Ap

Searching through Videos: Scholarly Information Search of Native and Non-Native English Speakers on YouTube

Living in a visually rich environment, university students seek and con-sume information through videos to complete their academic tasks. This exploratory pilot study examines if and how students’ interaction with the YouTube search engine will generate particular search experiences and out-comes on their search tasks, and how native and non-native English-speaking students may interact with the search system and the videos. It aims to explore possible patterns in the search behaviors and experiences of the two groups. One general exploratory information task and the partici-pants’ self-selected academic-oriented tasks were used for this study, both of which have been observed and analyzed along with follow-up interviews. Initial patterns have been observed in their behaviors within the search en-gine on their academic-oriented tasks. Limitations and suggestions for fur-ther development of the design of the research are discussed

Thermal activation energy of 3D vortex matter in NaFe1-xCoxAs (x=0.01, 0.03 and 0.07) single crystals

We report on the thermally activated flux flow dependency on the doping dependent mixed state in NaFe1-xCoxAs (x=0.01, 0.03, and 0.07) crystals using the magnetoresistivity in the case of B//c-axis and B//ab-plane. It was found clearly that irrespective of the doping ratio, magnetoresistivity showed a distinct tail just above the Tc, offset associated with the thermally activated flux flow (TAFF) in our crystals. Furthermore, in TAFF region the temperature dependence of the activation energy follows the relation U(T, B)=U_0 (B) (1-T/T_c )^q with q=1.5 in all studied crystals. The magnetic field dependence of the activation energy follows a power law of U_0 (B)~B^(-{\alpha}) where the exponent {\alpha} is changed from a low value to a high value at a crossover field of B=~2T, indicating the transition from collective to plastic pinning in the crystals. Finally, it is suggested that the 3D vortex phase is the dominant phase in the low-temperature region as compared to the TAFF region in our series samples

The Dropping of In-Medium Hadron Mass in Holographic QCD

We study the baryon density dependence of the vector meson spectrum using the D4/D6 system together with the compact D4 baryon vertex. We find that the vector meson mass decreases almost linearly in density at low density for small quark mass, but saturates to a finite non-zero value for large density. We also compute the density dependence of the $\eta\prime$ mass and the $\eta\prime$ velocity. We find that in medium, our model is consistent with the GMOR relation up to a few times the normal nuclear density. We compare our hQCD predictions with predictions made based on hidden local gauge theory that is constructed to model QCD.Comment: 20 pages, 7 figure