Volovik effect in the ±\pms-wave state for the iron-based superconductors

We studied the field dependencies of specific heat coefficient $\gamma(H) = \lim_{T \rightarrow 0} C(T,H)/T$ and thermal conductivity coefficient $\lim_{T \rightarrow 0} \kappa(T ,H)/T$ of the $\pm$s-wave state in the mixed state. We found that it is a generic feature of the two band s-wave state with the unequal sizes of gaps, small $\Delta_S$ and large $\Delta_L$, that Doppler shift of the quasiparticle excitations (Volovik effect) creates a finite density of states, on the extended states outside of vortex cores, proportional to $H$ in contrast to the $\sqrt{H}$ dependence of the d-wave state. Impurity scattering effect on the $\pm$s-wave state, however, makes this generic $H$-linear dependence sublinear approaching to the $\sqrt{H}$ behavior. Our calculations of $\lim_{T \rightarrow 0} \kappa(T ,H)/T$ successfully fit the experimental data of Ba(Fe$_{1-x}$Co$_x )_2$ As$_2$ with different Co-doping $x$ by systematically varying the gap size ratio $R= |\Delta_S | / |\Delta_L |$. We also resolve the dilemma of a substantial value of $\gamma(H \rightarrow 0)$ but almost zero value of $\lim_{T \rightarrow 0} \kappa(T ,H \rightarrow 0)/T$, observed in experiments.Comment: 5 pages, 2 figures accepted to Phys. Rev. Lett

Volovik effect on NMR measurements of unconventional superconuctors

We studied the Volovik effect on the NMR measurements of the two unconventional superconducting (SC) states, the d-wave and $\pm$s-wave states. We showed the generic field dependencies of the spin-lattice relaxation rate $1/T_1$ and Knight shift $K$ at low temperature limit in the pure cases as: $1/T_1 \propto H \log H$, $K \propto \sqrt{H}$ for the d-wave, and $1/T_1 \propto H$, $K \propto H$ for the $\pm$s-wave state, respectively. Performing numerical calculations we showed that these generic power laws survive for the good part of low field region with the realistic amount of impurities. We also found that the Volovik effect acts as an equivalent pair breaker as the unitary impurity scattering, hence induces the same temperature evolutions on $1/T_1$ and $K$, respectively, as the unitary impurities in both SC states. This finding implies that the Volovik effect should always be taken into account for the analysis of the NMR measurements in the mixed state.Comment: 5 pages, 4 figures; The fitting function of the inset of Fig.2(a) is slightly change

Russian Art Education: A Study on Post-Soviet Perspectives

This cross-cultural case study was conducted through questionnaire format by way of email correspondence with eight Russian art educators in May to June 2006. It was conducted to give an initial overview into Russian Art Education from the perspectives of eight Russian art educators. The data was analyzed to discover any commonalities in values, beliefs, and attitudes that may have significance to Americans wishing to learn about the structure, content, and pedagogy of Russian art education. The findings of this study reveal that Russian art educators embrace a very traditional and classical approach to the teaching of art. Today Russian art educators are also working toward a more democratic society through art education. The participant interview responses generally reflected a desire to positively communicate and express their educational ideas and beliefs. Recommendations include further research through additional case studies in different areas of the country and more English translations of Russian art education are suggested

Optimization of the neutron yield in fusion plasmas produced by Coulomb explosions of deuterium clusters irradiated by a petawatt laser

The kinetic energy of hot (multi-keV) ions from the laser-driven Coulomb explosion of deuterium clusters and the resulting fusion yield in plasmas formed from these exploding clusters has been investigated under a variety of conditions using the Texas Petawatt laser. An optimum laser intensity was found for producing neutrons in these cluster fusion plasmas with corresponding average ion energies of 14 keV. The substantial volume (1-10 mm(3)) of the laser-cluster interaction produced by the petawatt peak power laser pulse led to a fusion yield of 1.6x10(7) neutrons in a single shot with a 120 J, 170 fs laser pulse. Possible effects of prepulses are discussed. DOI: 10.1103/PhysRevE.87.023106Glenn Focht Memorial FellowshipNNSA DE-FC52-08NA28512DOE Office of Basic Energy SciencesPhysic

Are there nodes in LaFePO, BaFe2_2(AsP)2_2, and KFe2_2As2_2 ?

We reexamined the experimental evidences for the possible existence of the superconducting (SC) gap nodes in the three most suspected Fe-pnictide SC compounds: LaFePO, BaFe$_2$(As$_{0.67}$P$_{0.33}$)$_2$, and KFe$_2$As$_2$. We showed that while the $T$-linear temperature dependence of the penetration depth $\lambda(T)$ of these three compounds indicate extremely clean nodal gap superconductors, the thermal conductivity data $\lim_{T,H \rightarrow 0} \kappa_S (H,T)/T$ unambiguously showed that LaFePO and BaFe$_2$(As$_{0.67}$P$_{0.33}$)$_2$ are extremely dirty, while KFe$_2$As$_2$ can be clean. This apparently conflicting experimental data casts a serious doubt on the nodal gap possibility on LaFePO and BaFe$_2$(As$_{0.67}$P$_{0.33}$)$_2$.Comment: 11 pages, 5 figures A new section "4. Remark on the quantum oscillation (QO) experiments" is adde

Collapse arrest and soliton stabilization in nonlocal nonlinear media

We investigate the properties of localized waves in systems governed by nonlocal nonlinear Schrodinger type equations. We prove rigorously by bounding the Hamiltonian that nonlocality of the nonlinearity prevents collapse in, e.g., Bose-Einstein condensates and optical Kerr media in all physical dimensions. The nonlocal nonlinear response must be symmetric, but can be of completely arbitrary shape. We use variational techniques to find the soliton solutions and illustrate the stabilizing effect of nonlocality.Comment: 4 pages with 3 figure

Refractive index sensing in an all-solid twin-core photonic bandgap fiber

We describe a highly sensitive refractive index sensor based on a twin-core coupler in an all-solid photonic bandgap guiding optical fiber. A single hole acts as a microfluidic channel for the analyte, which modifies the coupling between the cores, and avoids the need for selective filling. By operating in the bandgap guiding regime the proposed sensor is capable of measuring refractive indices around that of water, and because the analyte varies the coupling coefficient (i.e., instead of phase matching condition) the device is capable of both high sensitivity and a relatively large dynamic range.8 page(s