A general scheme is developed to deal with 1D lattice systems that could be topologically complicated. It is aimed to give a complete study of two coupled normal metal rings. Our method starts with an investigation of the local expressions of the eig
enfunctions. By connecting different parts of the system, all the eigenvalues and eigenfunctions can be obtained. It is found that there is a possibility for the existence of localized states, which is beyond previous expectations.
We report the growth of single-crystalline Bi2Se3 nanoribbons with lengths up to several millimeters via a catalyst-free physical vapor deposition method. Scanning transmission electron microscopy analysis reveals that the nanoribbons grow along the
(1120) direction. We obtain a detailed characterization of the electronic structure of the Bi2Se3 nanoribbons from measurements of Shubnikov-de Haas (SdH) quantum oscillations. Angular dependent magneto-transport measurements reveal a dominant two-dimensional contribution originating from surface states and weak contribution from the bulk states. The catalyst-free synthesis yields high-purity nanocrystals enabling the observation of a large number of SdH oscillation periods and allowing for an accurate determination of the pi-Berry phase, one of the key features of Dirac fermions in topological insulators. The long-length nanoribbons can empower the potential for fabricating multiple nanoelectronic devices on a single nanoribbon.
We present specific heat measurements on a series of BaFe2(As1-xPx)2 single crystals with phosphorous doping ranging from x = 0.3 to 0.55. Our results reveal that BaFe2(As1-xPx)2 follows the scaling Delta_C/Tc ~ Tc^2 remarkably well. The clean-limit
nature of this material imposes new restraints on theories aimed at explaining the scaling. Furthermore, we find that the Ginzburg-Landau parameter decreases significantly with doping whereas the superconducting anisotropy is gamma~2.6, independent of doping.
Transition metal boride Ru$_7$B$_3$ was found to be a noncentrosymmetric superconductor with $T_{C}$ equal to 3.3 K. Superconducting and normal state properties of Ru$_7$B$_3$ were determined by a self-consistent analysis through resistivity($rho_{xx
}$ and $rho_{xy}$), specific heat, lower critical field measurement and electronic band structure calculation. It is found that Ru$_7$B$_3$ belongs to an s-wave dominated single band superconductor with energy gap 0.5 meV and could be categorized into type II superconductor with weak electron-phonon coupling. Unusual kink feature is clearly observed in field-broadening resistivity curves, suggesting the possible mixture of spin triplet induced by the lattice without inversion symmetry.
We report the synthesizing and characterization of the hole doped Ni-based superconductor ($La_{1-x}Sr_{x})NiAsO$. By substituting La with Sr, the superconducting transition temperature $T_c$ is increased from 2.4 K of the parent phase $LaNiAsO$ to 3
.7 K at the doping levels x= 0.1 - 0.2. The curve $T_c$ versus hole concentration shows a symmetric behavior as the electron doped samples $LaNiAs(O_{1-x}F_{x})$. The normal state resistivity in Ni-based samples shows a good metallic behavior and reveals the absence of spin density wave induced anomaly which appears in the Fe-based system at about 150 K. Hall effect measurements indicate that the electron conduction in the parent phase $LaNiAsO$ is dominated by electron-like charge carriers, while with more Sr doping, a hole-like band will emerge and finally prevail over the conduction, such a phenomenon reflects that the Fermi surface of $LaNiAsO$ comprises of electron pockets and hole pockets, thus the sign of charge carriers could be changed once the contribution of hole pockets overwhelms that of electron pockets. Magnetoresistance measurements and the violation of Kohler rule provide further proof that multiband effect dominate the normal state transport of ($La_{1-x}Sr_{x})NiAsO$.
