We systematically investigate the photoexcited (PE) quasiparticle (QP) relaxation and low-energy electronic structure in electron doped Ba(Fe1−x Cox )2As2 single crystals as a function of Co doping. The evolution of the photoinduced reflectivity transients with x proceeds with no abrupt changes. In the orthorhombic spin-density-wave (SDW) state, a bottleneck associated with a partial charge-gap opening is detected, similar to previous results in different SDW iron pnictides. The relative charge gap magnitude 2Δ(0)/kBTs decreases with increasing x. In the superconducting (SC) state, an additional relaxational component appears due to a partial (or complete) destruction of the SC state proceeding on a sub-0.5-picosecond timescale. The optical SC-state destruction energy, Up/kB = 0.3K/Fe, is determined near the optimal doping. The subsequent relatively slow recovery of the SC state indicates clean SC gaps. The T dependence of the transient reflectivity amplitude in the normal state is consistent with the presence of a pseudogap in the QP density of states. The polarization anisotropy of the transients suggests that the pseudogap-like behavior might be associated with a broken fourfold rotational symmetry resulting from nematic electronic fluctuations persisting up to T ~ 200 K at any x. The second moment of the Eliashberg function, obtained from the relaxation rate in the metallic state at higher temperatures, indicates a moderate electron phonon coupling, λ ~0.3.
COBISS.SI-ID: 25970215
We extend the theory of hopping magnetoresistance to states with nonzero orbital momenta. This results in a negative weak-field magnetoresistance, which is linear in magnetic field when the orbital degeneracy is lifted.
COBISS.SI-ID: 25766439
We describe a straightforward technique to synthesize pure Mo nanowires (NWs) from Mo6SyIz (8,2 ( y + z ≤ 10) NWs as precursor templates. The structural transformations occur when Mo6SyIz NWs are annealed in Ar/H2 mixture leading to the formation of pure Mo NWs with similar structures as initial morphologies. Detailed microscopic characterizations show that large diameters ()15 nm) Mo NWs are highly porous, while small diameters ((7 nm) are made of solid nanocrystalline grains. We find NW of diameter 4 nm can carry up to 30 μA current without suffering structural degradation. Moreover, NWs can be elastically deformed over several cycles without signs of plastic deformation.
COBISS.SI-ID: 26364455
The application of a positive or negative local bias to the surface of La[sub]{1.975}Sr[sub]{0.025}CuO[sub]{4+[delta]} (LSCO) crystal by a conducting atomic force microscope tip results in accumulation of a (positive or negative respectively) metastable charge on the surface. The surface charge initially shows diffusive dynamics with a timescale of hours, but thereafter it is shown to be stable for months. The charged regions are found by Auger electron spectroscopy to have a different stoichiometry from the surrounding material. A part from fundamental implications for the heterostructure device construction, such surface charge manipulation could lead to AFM nanopatterning of superconducting nanoscale device and applications memories.
COBISS.SI-ID: 899242
The subject of the invention is a method for a synthesis of one-dimensional structures, such as nanowires, microwires and nanobelts of 4d and 5d transition metals (Nb, Mo Ta, W). The invention belongs to the field of inorganic chemistry and chemistry of transition metals. The invention refers to a synthesis of quasi one-dimensional structures of transition metals by using a method of conversion of quasi one-dimensional compounds with a submicron cross-section of nanowires described with formula M6CyHz, 8,2(y+z 10, wherein M is a transition metal (Nb, Mo Ta, W), C is a chalcogen (sulphur (S), selenium (Se), tellurium (Te)); H is a halogen (iodine (I)) by heating in the presence of hydrogen. This method provides for a synthesis of quasi one-dimensional structures, such as nanowires, microwires and nanobelts of 4d and 5d transition metals (Nb, Mo Ta, W).
COBISS.SI-ID: 25491751