We present magnetotransport studies on a series of BaFe2_xNixAs2 （0.03 〈 x 〈 0.10） single crystals. In the un- derdoped （x = 0.03） non-superconducting sample, the temperature-dependent resistivity exhibits a peak at 22 K, which is associated with the onset of filamentary superconductivity （FLSC）. FLSC is suppressed by an external magnetic field in a manner similar to the suppression of bulk superconductivity in an optimally-doped （x = 0.10） compound, suggesting the same possible origin as the bulk superconductivity. Our magnetoresistivity measurements reveal that FLSC persists up to the optimal doping and disappears in the overdoped regime where the long-range antiferromagnetic order is completely suppressed, pointing to a close relation between FLSC and the magnetic order.
Dear Editors, Tungsten ditelluride （WTe2） is a layered transition-metal dichalcogenide （TMD）. The tungsten layers are clipped by adjacent chalcogenide layers. The sandwich structure stacks along the c-axis with Van Der Waals bonding between layers. Particularly, tungsten chains are formed along the a-axis within the dichalcogenide layers.
We performed detailed temperature-dependent optical measurements on optimally doped Ba0.6K0.4Fe2As2 single crystal, We examine the changes of the in-plane optical conductivity spectral weight in the normal state and the evolution of the superconducting condensate in the superconducting state. In the normal state, the low-frequency spectral weight shows a metallic response with an arctan （T） dependence, indicating a T-linear scattering rate behavior for the carriers. A high energy spectral weight transfer associated with the Hund＇s coupling occurs from the low frequencies below 4000 cm^-1 5000 cm^-1 to higher frequencies up to at least 104 cm^-1. Its temperature dependence analysis suggests that the Hund＇s coupling strength is continuously enhanced as the temperature is reduced. In the superconducting state, the FGT sum rule is conserved according to the spectral weight estimation within the conduction bands, only about 40% of the conduction bands participates in the superconducting condensate indicating that Ba0.6K0.4Fe2As2 is in dirty limit.
We present an infrared spectroscopy study of charge dynamics in CaCo_2As_2 single crystal. In this material, the optical conductivity can be described by two Drude components with different scattering rates（1/τ）： a broad incoherent background and a narrow Drude component. By monitoring the temperature dependence, we find that only the narrow Drude component is temperature-dependent and determines the transport properties. Especially a Fermi liquid behavior of carriers is revealed by the T^2 behavior in the dc resistivity ρ_n and scattering rate 1/τ_n, indicating a coherent nature of quasiparticles in the narrow Drude subsystem.
Magnetoresistance in superconducting Nb films perforated with rectangular arrays of antidots （holes） is investigated at various temperatures and currents. Normally, the magnetoresistance increases with the increasing magnetic field. In this paper, we report a reverse behavior in a certain range of high fields after vortex reconfiguration transition, where the resistances at non-matching fields are smaller than those in the low field regime. This phenomenon is due to a strong caging effect, in which the interstitial vortices are trapped among the pinned multiquanta vortices. This effect is temperature and current dependent.
We measured the infrared reflectivity of BaFe1.904Ni0.096As2 single crystal from room temperature down to 20 K. Two Drude terms and a Lorentz term well describe the real part of the optical conductivity σ1 （ω）. We fit the reciprocal of static optical conductivity 1/σ1（0） by the power law ρ （T）=ρo＋ATn with n= 1.6. The ＂broad＂ Drude component exhibits an incoherent background with a T-independent scattering rate 1/τb, while the other ＂narrow＂ one reveals a T-quadratic scattering rate 1/τn, indicating a hidden Fermi-liquid behavior in BaFe1.904Nio.096As2 compound.
Carbon-based spintronics refers mainly to the spin injection and transport in carbon materials including carbon nanotubes,graphene,fullerene,and organic materials.In the last decade,extraordinary development has been achieved for carbon-based spintronics,and the spin transport has been studied in both local and nonlocal spin valve devices.A series of theoretical and experimental studies have been done to reveal the spin relaxation mechanisms and spin transport properties in carbon materials,mostly for graphene and carbon nanotubes.In this article,we provide a brief review on spin injection and transport in graphene,carbon nanotubes,fullerene and organic thin films.
