Magnetotransport Properties of a Nodal Line Semimetal TiSi

We report the magnetoresistance(MR), de Haas-van Alphen(dHvA) effect and Hall effect measurements on a single crystal of TiSi, which is predicted to be a nodal line semimetal. With application of a magnetic field, a metal-to-insulator-like transition in ρ(T) and a nonsaturating MR are observed at low temperatures. The dHvA oscillations reveal a small Fermi-surface pocket with a nontrivial Berry phase. The analysis of the nonlinear Hall resistivity shows that TiSi is a multiband system with low carrier densities and high mobilities. All these results unambiguously prove the existence of Dirac fermions in TiSi.     

Negative Longitudinal Magnetoresistance in the (8-Axis Resistivity of Cd

We report a systematic study on magnetotransport properties of the single crystal of cadmium(Cd). When the applied magnetic field B is perpendicular to the current I, the resistivities for both directions(I ‖ a, I ‖ c) show field induced metal-to-insulator-like transitions. The isothermal magnetoresistance(MR) at low temperatures increases approximately as the square of the magnetic field without any sign of saturation, and reaches up to 1140000% and 58000% at T = 2 K and B = 9 T for I ‖ a and I ‖ c, respectively. As the magnetic field rotates to parallel to the current, no sign of negative MR is observed for I ‖ a, while an obvious negative MR appears up to-70% at 2 K and 9 T for the current flowing along the c-axis, and the negative longitudinal MR shows a strong dependence of the electrode position on the single crystal. These results suggest that the negative longitudinal MR is caused by the dislocations formed in the process of crystal growing along the c-axis. Further studies are needed to clarify this point.     

Magnetic and Transport Properties of the Kondo Lattice Compound YbPtAs

We report the electrical resistivity, magnetic susceptibility, and heat capacity studies on a new intermetallic compound YbPtAs, which crystallizes in a modified AIB2 type structure. The Yb ions in YbPtAs are in a trivalent state and order antiferromagnetically around Neel temperatures T_(N1) = 6.5 K and T_(N2) = 2.2 K,respectively,deduced both from the magnetic susceptibility χ(T) and heat capacity C(T) measurements. The magnetic contribution in resistivity, ρ_m(T), exhibits a broad maximum at around 100 K and a logarithmic temperature dependence in the high-temperature region, indicative of the presence of the Kondo effect in YbPtAs.     

Electric Field Induced Permanent Superconductivity in Layered Metal Nitride Chlorides HfNCl and ZrNCl

Devices of electric double-layer transistors(EDLTs) with ionic liquid have been employed as an effective way to dope carriers over a wide range. However, the induced electronic states can hardly survive in the materials after releasing the gate voltage V_G at temperatures higher than the melting point of the selected ionic liquid. Here we show that a permanent superconductivity with transition temperature T_c of 24 and 15 K is realized in single crystals and polycrystalline samples of HfNCl and ZrNCl upon applying proper V_G's at different temperatures.Reversible change between insulating and superconducting states can be obtained by applying positive and negative V_G at low temperature such as 220 K, whereas V_G's applied at 250 K induce the irreversible superconducting transition. The upper critical field H_(c2) of the superconducting states obtained at different gating temperatures shows similar temperature dependence. We propose a reasonable scenario that partial vacancy of Cl ions could be caused by applying proper V_G's at slightly higher processing temperatures, which consequently results in a permanent electron doping in the system. Such a technique shows great potential to systematically tune the bulk electronic state in the similar two-dimensional systems.