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A wideband dual-polarized Vivaldi antenna covering 1.85-18.3 GHz band with enhanced gain is presented in this letter. The proposed antenna consists of two Vivaldi antenna elements (VAEs), which are designed based on the conventional Vivaldi antenna. Dual-slot structure is employed to improve the gain of the conventional Vivaldi antenna. As a result, spherical-like waves across the slot aperture of the conventional Vivaldi antenna can be transformed to be plane-like waves and thus gain enhancement can be achieved. In order to extend lower frequency limit of the VAE, elliptical slots are adopted. The proposed dual-polarized Vivaldi antenna is obtained by combining two VAEs in a cross-shaped form. The prototype is simulated, fabricated, and measured. A good agreement between EM simulated and measured results evidently validates the proposed antenna. [ABSTRACT FROM AUTHOR]

We report measurements of the specific heat and electrical resistivity of Ca3(Ir0.91Co0.09)4Sn13 in comparison to Ca3Ir4Sn13. The Co substitution was chosen to suppress the structural anomaly T*=38K reported in Ca3Ir4Sn13. While the superconducting transition temperature of Ca3(Ir0.91Co0.09)4Sn13 is slightly higher than in the stoichiometric parent compound Ca3Ir4Sn13, and it displays a stronger superconducting coupling strength, the absence of a structural phase transition allows us to determine the spectral distribution of phonon states and its relation to superconductivity. The phonon density of states F(w) and the spectral electron-phonon scattering function atr²F(w) are determined by deconvolution of the specific heat and electrical resistivity, respectively. A dominant mode appears in both histograms at hw=12meV, which indicates that this phonon mode is responsible for the superconductivity in Ca3(Ir0.91Co0.09)4Sn13. The data suggest that superconductivity in this material class can be conclusively explained within a conventional strong -coupling phonon-mediated scenario. [ABSTRACT FROM AUTHOR]

The hole doped Fe-based superconductors Ba1-xAxFe2As2 (where A=Na or K) show a particularly rich phase diagram. It was observed that an intermediate reentrant tetragonal phase, in which the C4 fourfold rotational symmetry is restored, forms within the orthorhombic antiferromagnetically ordered stripe-type spin density wave state above the superconducting transition [S. Avci et al., Nat. Commun. 5, 3845 (2014); A. E. Böhmer et al., Nat. Commun. 6, 7911 (2015)]. A similar intermediate phase was reported to appear if pressure is applied to underdoped Ba1-xKxFe2As2 [E. Hassinger et al., Phys. Rev. B 86, 140502(R) (2012)]. Here we report data of the electric resistivity, Hall effect, specific heat, and the thermoelectric Nernst and Seebeck coefficients measured on a Ba0.85K0.15Fe2As2 single crystal under pressure up to 5.5 GPa. The data reveal a coexistence of the intermediate phase with filamentary superconductivity. The Nernst coefficient shows a large signature of nematic order that coincides with the stripe-type spin density wave state up to optimal pressure. In the pressure-induced intermediate phase the nematic order is removed, thus confirming that its nature is a reentrant tetragonal phase. [ABSTRACT FROM AUTHOR]

We fabricate high-mobility p-type few-layer WSe2 field-effect transistors and surprisingly observe a series of quantum Hall (QH) states following an unconventional sequence predominated by odd-integer states under a moderate strength magnetic field. By tilting the magnetic field, we discover Landau level crossing effects at ultralow coincident angles, revealing that the Zeeman energy is about 3 times as large as the cyclotron energy near the valence band top at the Γ valley. This result implies the significant roles played by the exchange interactions in p-type few-layer WSe2, in which itinerant or QH ferromagnetism likely occurs. Evidently, the Γ valley of few-layer WSe2 offers a unique platform with unusually heavy hole carriers and a substantially enhanced g factor for exploring strongly correlated phenomena. [ABSTRACT FROM AUTHOR]