Hiroshi Takatsu

Extremely Large Magnetoresistance in the Nonmagnetic Metal PdCoO_{2}

Extremely large magnetoresistance is realized in the nonmagnetic layered metal PdCoO(2). In spite of a highly conducting metallic behavior with a simple quasi-two-dimensional hexagonal Fermi surface, the interlayer resistance reaches up to 35,000% for the field along the [11[over ¯]0] direction. Furthermore, the temperature dependence of the resistance becomes nonmetallic for this field direction, while it remains metallic for fields along the [110] direction. Such severe and anisotropic destruction of the interlayer coherence by a magnetic field on a simple Fermi surface is ascribable to orbital motion of carriers on the Fermi surface driven by the Lorentz force, but seems to have been largely overlooked until now.

Correlation between crystal structure and superconductivity in LaO0.5F0.5BiS2

Abstract Correlation between crystal structure and superconducting properties of the BiS2-based superconductor LaO0.5F0.5BiS2 was investigated. We have prepared LaO0.5F0.5BiS2 polycrystalline samples with various lattice constants. It was found that high-pressure annealing generated uniaxial strain along the c axis. Further, the highly-strained sample showed higher superconducting properties. We concluded that the uniaxial strain along the c axis was positively linked with the enhancement of superconductivity in the LaO1−xFxBiS2 system.

Quantum Oscillations and High Carrier Mobility in the Delafossite PdCoO2

We present de Haas-van Alphen and resistivity data on single crystals of the delafossite PdCoO(2). At 295 K we measure an in-plane resistivity of 2.6  μΩ cm, making PdCoO(2) the most conductive oxide known. The low-temperature in-plane resistivity has an activated rather than the usual T(5) temperature dependence, suggesting a gapping of effective scattering that is consistent with phonon drag. Below 10 K, the transport mean free path is ∼20  μm, approximately 10(5) lattice spacings and an astoundingly high value for flux-grown crystals. We discuss the origin of these properties in light of our data.

Bulk Superconductivity in Bi4O4S3 Revealed by Specific Heat Measurement

Specific heat experiments on a well-characterized polycrystalline sample of the BiS2 based superconductor Bi4O4S3 revealed that it shows a crear specific heat anomaly at about Tc = 4.4 K, consistent with Tc from the resistivity and dc susceptibility. This observation indicates the superconductivity of Bi4O4S3 to be bulk in nature.

Unconventional anomalous hall effect in the metallic triangular-lattice magnet PdCrO₂.

We experimentally reveal an unconventional anomalous Hall effect (UAHE) in a quasi-two-dimensional triangular-lattice antiferromagnet PdCrO₂. Using high quality single crystals of PdCrO₂, we found that the Hall resistivity ρ(xy) deviates from the conventional behavior below T*≃20 K, noticeably lower than T(N)=37.5 K, at which Cr³+ (S=3/2) spins order in a 120° structure. In view of the theoretical expectation that the spin chirality cancels out in the simplest 120° spin structure, we discuss required conditions for the emergence of UAHE within Berry-phase mechanisms.

Critical behavior of the metallic triangular-lattice Heisenberg antiferromagnet PdCrO 2

We report physical properties of the conductive magnet

Roles of High-Frequency Optical Phonons in the Physical Properties of the Conductive Delafossite PdCoO2

{\text{PdCrO}}_{2}

Heavy-Mass Behavior of Ordered Perovskites ACu3Ru4O12 (A = Na, Ca, La)

consisting of a layered structure with a triangular lattice of

Long-range order and spin-liquid states of polycrystalline Tb2+xTi2-xO7+y

{\text{Cr}}^{3+}

Anisotropy of the superconducting state in Sr2RuO4.

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