Minhyea Lee

Large enhancement of the thermopower in NaxCoO2 at high Na doping

Research on the oxide perovskites has uncovered electronic properties that are strikingly enhanced compared with those in conventional metals. Examples are the high critical temperatures of the cuprate superconductors and the colossal magnetoresistance in the manganites. The conducting layered cobaltate NaxCoO2 exhibits several interesting electronic phases as the Na content x is varied1,2,3,4, including water-induced superconductivity4 and an insulating state3 that is destroyed by field5. Initial measurements1 showed that, in the as-grown composition, NaxCoO2 has moderately large thermopower S and conductivity σ. However, the prospects for thermoelectric cooling applications faded when the figure of merit Z was found to be small at this composition (0.60.75, S undergoes an even steeper enhancement. At the critical doping xp∼0.85, Z (at 80 K) reaches values ∼40 times larger than in the as-grown crystals. We discuss prospects for low-temperature thermoelectric applications.

Structures and thermoelectric properties of the infinitely adaptive series "Bi2…m"Bi2Te3…n

The structures and thermoelectric properties of the Bi2mBi2Te3n homologous series, derived from stacking hexagonal Bi2 and Bi2Te3 blocks, are reported. The end members of this series are metallic Bi and semiconducting Bi2Te3; nine members of the series have been studied. The structures form an infinitely adaptive series and a unified structural description based on a modulated structure approach is presented. The as-synthesized samples have thermopowers S that vary from n type for Bi2Te3 to p type for phases rich in Bi2 blocks but with some Bi2Te3 blocks present, to n type again for Bi metal. The thermoelectric power factor S 2 / is highest for Bi metal 43 W/K 2 cm at 130 K, followed by Bi2Te3 20 W/K 2 cm at 270 K, while Bi2Te m:n=5:2 and Bi7Te3 m:n=15:6 have 9 W/K 2 cm at 240 K and 11 W/K 2 cm at 270 K, respectively. The results of doping studies with Sb and Se into Bi2Te are reported.

Hidden constant in the anomalous Hall effect of high-purity magnet MnSi

Measurements of the Hall conductivity in MnSi can provide incisive tests of theories of the anomalous Hall (AH) effect, because both the mean-free-path and magnetoresistance (MR) are unusually large for a ferromagnet. The large MR provides an accurate way to separate the AH conductivity

High resolution study of magnetic ordering at absolute zero

\sigma_{xy}^A

Anomalous Thermal Conductivity and Magnetic Torque Response in the Honeycomb Magnet α−RuCl3

from the ordinary Hall conductivity

Quantum superposition of a single microwave photon in two different ’colour’ states

\sigma_{xy}^N

Anomalous Hall effect and magnetoresistance in the layered ferromagnet Fe1/4TaS2 : The inelastic regime

. Below the Curie temperature

Structural and transport properties of epitaxial NaxCoO2 thin films

T_C

Giant magnetothermopower associated with large magnetoresistance in Ag2−δTe

,

Noise performance of lumped element direct current superconducting quantum interference device amplifiers in the 4–8 GHz range

\sigma_{xy}^A