Hidden non-Fermi liquid behavior caused by magnetic phase transition in Ni-doped Ba-122 pnictides

We studied two BaFe2−x Ni x As2 (Ni-doped Ba-122) single crystals at two different doping levels (underdoped and optimally doped) using an optical spectroscopic technique. The underdoped sample shows a magnetic phase transition around 80 K. We analyze the data with a Drude-Lorentz model with two Drude components (D1 and D2). It is known that the narrow D1 component originates from electron carriers in the electron-pockets and the broad D2 mode is from hole carriers in the hole-pockets. While the plasma frequencies of both Drude components and the static scattering rate of the broad D2 component show negligible temperature dependencies, the static scattering rate of the D1 mode shows strong temperature dependence for the both samples. We observed a hidden quasi-linear temperature dependence in the scattering rate of the D1 mode above and below the magnetic transition temperature while in the optimally doped sample the scattering rate shows a more quadratic temperature dependence. The hidden non-Fermi liquid behavior in the underdoped sample seems to be related to the magnetic phase of the material.

STM/STS STUDY ON LOCAL ELECTRONIC STATES OF UNDERDOPED Bi2Sr2CaCu2O8+δ

Spatial variation of low temperature tunneling spectrum on atomic scale was examined on the slightly underdoped Bi 2212 sample (Tc~74 K , p~0.12) by using a STM/STS technique. We observed a V-shaped gap with sharp coherence peaks, which is expected for d-wave superconductors, over the distance of ~18 nm and no other kind of gap. The spatial variation of gap size Δ0 is small, ranging from 41 to 53 meV . These results indicate that the superconductivity takes place rather homogeneously in the slightly underdoped sample.

LOW-TEMPERATURE NORMAL-STATE HALL EFFECT IN HIGH-TcBi2Sr2-xLaxCuO6+δ REVEALED BY 60 T MAGNETIC FIELDS

We report low-temperature Hall coefficient in the normal state of the high-Tc superconductor Bi 2 Sr 2-x La x CuO 6+δ. The Hall coefficient was measured down to 0.5 K by suppressing superconductivity with a 60 T pulsed magnetic field. The carrier concentration was varied from overdoped to underdoped regimes by partially substituting Sr with La in a set of five samples. The observed saturation of the Hall coefficient at low temperatures suggests the ability to extract the carrier concentration of each sample. The most underdoped sample exhibits a diverging Hall coefficient at low temperatures, consistent with a depletion of carriers in the insulating ground state. The Hall number exhibits a sharp peak providing additional support for the existence of a phase boundary at the optimal doping.

INTERPLAY BETWEEN TRANSPORT, MAGNETIC-, AND STRUCTURAL PROPERTIES OF MN-PEROVSKITES WITH VARIOUS DOPING LEVEL

We performed a comparative study on the colossal negative magnetoresistivity and the Hall effect in thin films of the manganese perovskite La 1-x Ca x MnO 3 with x =0.3 and x =0.67. The underdoped sample ( x =0.3) undergoes a phase transition from a paramagnetic semiconductor to a ferromagnetic quasimetal at the Curie temperature T C =280 K , while the overdoped compound ( x =0.67) stays a paramagnetic semiconductor at all temperatures. Both materials show colossal negative magneto-resistivity, albeit on considerably different temperature- and field scales, depending on the magnetic interactions between neighbouring Mn ions. According to the Hall data, the charge carriers in the underdoped material are hole-type, partially compensated by an electron-type contribution. The overdoped system shows electronic carriers with a thermally activated concentration. The ordinary Hall effect is in both compounds superimposed by an anomalous Hall contribution with a sign opposite to the intrinsic charge-carrier type.