Quantum point contact conductance in normal metal/insulator/ metal/dx2−y2+idxy mixed wave superconductor junctions

The tunneling conductance in a normal metal/insulator/metal/$d_{x^2?y^2}+i{d}_{xy}$ mixed wave superconductor (N/I/N/$d_{x^2?y^2}+i{d}_{xy}$) junction is calculated, where the N/I/N region is a quantum wire. It is found in the single-mode case that the magnitude of the tunneling conductance near zero voltage is enhanced due to the Andreev bound state by quasiparticles with perpendicular and horizontal injection, and the zero-bias conductance varies with $L$ ($L$ is the distance from insulating layer to the interface of N/$d_{x^2?y^2}+i{d}_{xy}$ mixed wave superconductor). Splitting of the zero-bias conductance peak appears in the quantum point contact tunneling spectra for an N/I/N/$d_{x^2?y^2}+i{d}_{xy}$ junction, and several subgap peaks can split at the same time. On increasing both $L$ and the magnitude ratio of the two components for the $d_{x^2?y^2}+i{d}_{xy}$ mixed wave, the subgap resonances exhibit an alternately high and low behavior inside the energy gap. These results are different from those in d-wave and p-wave superconductor junctions.     

Luminescent properties of Yb-doped LaSc3(BO3)4 under VUV excitation

Ytterbium doped borate crystals are promising laser media, e.g. in ${\mathrm{LaSc}}_3({\mathrm{BO}}_3{)}_4$ (LSB) matrices large distance between ytterbium ions results in reduced concentration quenching of the ytterbium f–f luminescence [Petermann, K., Fagundes-Peters, D., Johansen, O., Mond, M., Peters, V., Romero, J.J., Kutovoi, S., Speiser, J., Giesen, A., 2005. Highly Yb-doped oxides for thin-disc lasers. J. Crystal Growth 275, 135-140]. ${\mathrm{Yb}}^{3+}$ ions in complex oxides in addition to the 4f $\to$ 4f transitions often manifest fast charge transfer luminescence (CTL) in the UV-visible range. In some borates it was not observed at all, like in orthoborates of Sc, Y and La [Van Pieterson, L., Heeroma, M., de Heer, E., Meijerink, A., 2000. Charge transfer luminescence of ${\mathrm{Yb}}^{3+}$. J. Lumin. 91, 177–193]; in haloborates ${\mathrm{Sr}}_2{\mathrm{B}}_5{\mathrm{O}}_9\mathrm{X}$, where X = Cl, Br, the UV/visible luminescence was attributed to ytterbium CTL though it looked substantially different from other matrices [Dotsenko, V.P., Berezovskaya, I.V., Pyrogenko, P.V., Efryushina, N.P., Rodniy, P.A., Eijk van, C.W.E., Sidorenko, A.V., 2002. Valence states and luminescence properties of ytterbium ions in strontium haloborates. J. Solid State Chem. 166, 271–276]; while in oxyborate ${\mathrm{Li}}_2{\mathrm{Lu}}_5{\mathrm{O}}_4({\mathrm{BO}}_3{)}_3$ “classical” CTL was observed [Jubera, V., Garcia, A., Chaminade, J.P., Guillen, F., Sablayrolles, Jean, Fouassier, C., 2007. ${\mathrm{Yb}}^{3+}$ and ${\mathrm{Yb}}^{3+}\text{-}{\mathrm{Eu}}^{3+}$ luminescent properties of the ${\mathrm{Li}}_2{\mathrm{Lu}}_5{\mathrm{O}}_4({\mathrm{BO}}_3{)}_3$ phase. J. Lumin. 124(1), 10–14]. In this work the luminescence properties of another borate, namely LSB doped by Yb are presented.     

Monopoles on the Bryant–Salamon G2-manifolds

$G_2$-monopoles are solutions to gauge theoretical equations on noncompact $7$-manifolds of $G_2$ holonomy. We shall study this equation on the $3$ Bryant–Salamon manifolds. We construct examples of $G_2$-monopoles on two of these manifolds, namely the total space of the bundle of anti-self-dual two forms over the ${\mathbb{S}}^4$ and ${\mathbb{C}\mathbb{P}}^2$. These are the first nontrivial examples of $G_2$-monopoles.Associated with each monopole there is a parameter $m\in {\mathbb{R}}^{+}$, known as the mass of the monopole. We prove that under a symmetry assumption, for each given $m\in {\mathbb{R}}^{+}$ there is a unique monopole with mass $m$. We also find explicit irreducible $G_2$-instantons on ${\Lambda }_{-}^2\left({\mathbb{S}}^4\right)$ and on ${\Lambda }_{-}^2\left({\mathbb{C}\mathbb{P}}^2\right)$.The third Bryant–Salamon $G_2$-metric lives on the spinor bundle over the $3$-sphere. In this case we produce a vanishing theorem for monopoles.     

Pressure dependence of negative thermal expansion in Zr2(WO4)(PO4)2

Negative thermal expansion materials can experience significant stresses when they are used in composites. Under ambient conditions Zr₂(WO₄)(PO₄)₂ displays anisotropic negative thermal expansion (NTE) (${\alpha }_v=?14.0\left(10\right)\times 10^{?6}{K}^{?1}$, ${\alpha }_a=?7.9\left(5\right)\times 10^{?6}{K}^{?1}$, ${\alpha }_b=2.5\left(5\right)\times 10^{?6}{K}^{?1}$, ${\alpha }_c=?8.7\left(2\right)\times 10^{?6}{K}^{?1}$ at 0 GPa). The effect of hydrostatic pressure on its thermal expansion characteristics was investigated by neutron diffraction between 300 and 60 K at pressures up to 0.3 GPa. No phase transitions were observed in the pressure and temperature range examined. The material was found to have a bulk modulus, B₀, of 61.3(8) GPa at ambient temperature, and unlike some other NTE materials, pressure had no detectable effect on thermal expansion (${\alpha }_v=?14.2\left(8\right)\times 10^{?6}{K}^{?1}$, ${\alpha }_a=?7.9\left(3\right)\times 10^{?6}{K}^{?1}$, ${\alpha }_b=2.9\left(5\right)\times 10^{?6}{K}^{?1}$, ${\alpha }_c=?9.2\left(2\right)\times 10^{?6}{K}^{?1}$ at 0.3 GPa).     

Pseudo anti-commuting and Ricci soliton real hypersurfaces in complex two-plane Grassmannians

In this paper, first we introduce a new notion of pseudo anti-commuting for real hypersurfaces in complex two-plane Grassmannians $G_2\left({\mathbb{C}}^{m+2}\right)$ and prove a complete classification theorem, which gives a shrinking Ricci soliton with potential Reeb flow on Hopf real hypersurfaces and a tube over a totally real totally geodesic $\mathbb{Q}{P}^n$, $m=2n$ in $G_2\left({\mathbb{C}}^{m+2}\right)$.     

Thermoelectric and topological properties of half-Heusler compounds ZrIrX(As,Sb, Bi)

The strain dependent electronic structures, thermoelectric and topological properties of the half-Heusler compounds ZrIrX(X=As, Sb, Bi) are investigated by the first-principle calculations. At the equilibrium lattice constants, all the three compounds are trivial insulators and good thermoelectric materials with the Seebeck coefficient S and the power factor over relaxation time $S^2\sigma /\tau$ as large as 1180 (μV/K) and 4.1 (${10}^{11}W{m}^{?1}{K}^{?2}{s}^{?1}$), respectively. The compressive strain enhances the band gap, while the tensile strain decreases the band gap. At some specific tensile strains, the compounds become Dirac-semimetals, with the s-type band ${\mathrm{\Gamma }}_6$ below p-type band ${\mathrm{\Gamma }}_8$, in the cubic phase. When we compress the a(b)-axis and elongate the c-axis of the compounds, they become the type-I Weyl semimetals. For ZrIrAs, the eight Weyl-Points (WPS) locate at (± K_x, 0, ± K_z), (0, ± K_y, ± K_z), ${\mathrm{K}}_x={\mathrm{K}}_y=0.008{\mathrm{\AA }}^{?1}$, ${\mathrm{K}}_z=0.043{\mathrm{\AA }}^{?1}$.     

Lattice dynamics and phase transition of NiTi alloy

We have performed detailed first-principles calculations to investigate the structural and lattice dynamical properties of NiTi alloy. The calculated static structures consist well with the experimental data and other theoretical results. With quasi harmonic approximation, the phase boundary between B19′ and BCO phases can be described as a five order polynomial $T=100?89.28P+296.75P^2?717.94P^3+734.62P^4?274.25P^5$. The change of vibrational entropy is $0.07k_B$/atom at the transition temperature 100 K under zero pressure.     

Disorder dependence electron phonon scattering rate of V82Pd18 − xFex alloys at low temperature

We have systematically investigated the disorder dependence electron phonon scattering rate in three dimensional disordered V₈₂Pd_18 ? xFe_x alloys. A minimum in temperature dependence resistivity curve has been observed at low temperature $T=T_{\mathrm{m}}$. In the temperature range $5\text{ K}\le T\le T_{\mathrm{m}}$ the resistivity correction follows ${{\rho }_{\mathrm{o}}}^{5/2}{T}^{1/2}$ law. The dephasing scattering time has been calculated from analysis of magnetoresistivity by weak localization theory. The electron dephasing time is dominated by electron–phonon scattering and follows anomalous temperature (T) and disorder $({\rho }_0)$ dependence behaviour like ${\tau }_{\mathrm{e}\text{-}\mathrm{ph}}^{?1}\propto T^2/{\rho }_0$, where ${\rho }_0$ is the impurity resistivity. The magnitude of the saturated dephasing scattering time $({\tau }_0)$ at zero temperature decreases with increasing disorder of the samples. Such anomalous behaviour of dephasing scattering rate is still unresolved.