K. Uchinokura

Magnetic-field-induced condensation of triplons in Han Purple pigment BaCuSi2O6.

Besides being an ancient pigment, BaCuSi2O6 is a quasi-2D magnetic insulator with a gapped spin dimer ground state. The application of strong magnetic fields closes this gap, creating a gas of bosonic spin triplet excitations. The topology of the spin lattice makes BaCuSi2O6 an ideal candidate for studying the Bose-Einstein condensation of triplet excitations as a function of the external magnetic field, which acts as a chemical potential. In agreement with quantum Monte Carlo numerical simulations, we observe a distinct lambda anomaly in the specific heat together with a maximum in the magnetic susceptibility upon cooling down to liquid helium temperatures.

Spin-Vacancy-Induced Long-Range Order in a New Haldane-Gap Antiferromagnet

Magnetic susceptibility, high-field magnetization, and inelastic neutron scattering experiments are used to study the magnetic properties of a new S=1 quasi-one-dimensional antiferromagnet PbNi{sub 2}V {sub 2}O{sub 8} . Interchain interactions are shown to be almost, but not quite, strong enough to destroy the nonmagnetic singlet ground state and the energy gap in the magnetic excitation spectrum. Substituting nonmagnetic Mg{sup 2+} (S=0 ) ions for Ni{sup 2+} (S=1 ) induces a magnetically ordered state at low temperatures. To our knowledge this is the first observation of doping-induced long-range order in a Haldane-gap system. {copyright} {ital 1999} {ital The American Physical Society }

Raman Scattering and Infrared Reflectance in 2H-MoSe2

Raman scattering and infrared reflectance have been measured in 2H-MoSe 2 . We observed all Raman-active modes, A 1g , E 1g , E 2g 1 and E 2g 2 , and two infrared-active modes, E 1u 2 and A 2u 2 . Intralayer force constants are estimated from the central force model. The bond between metal (Mo) and chalcogen (Se) predominates over the high-lying phonon frequencies with long wavelength. On the other hand, interlayer shear force constant is estimated from the frequency of E 2g 2 mode, that is a rigid-layer mode, and is much smaller than the intralayer force constants. This fact, which is similar to that in other group VIB transition-metal dichalcogenides, reflects that the interlayer interaction is due to van der Waals force. The second-order Raman spectrum has been also observed and discussed.

High transition temperature superconductor LaBa2Cu3O7−y with zero resistance at 92 K

Samples of LaBa2 Cu3 O7−y have been synthesized, which show a superconducting transition above 90 K. One of the samples shows a superconducting transition with an onset at 93 K and a zero resistivity at 92 K. These temperatures are the highest among those reported so far on this system and even higher than those in YBa2 Cu3 O7−y. The magnetic susceptibility measurement also shows that it has a superconducting transition with onset at around 93 K. To synthesize such good LaBa2 Cu3 O7−y requires two important procedures. First is sintering above 950 °C in N2 gas atmosphere and the second is annealing at 300 °C in dried O2 gas atmosphere.

Dispersive Raman Mode of Layered Compound 2H-MoS2 under the Resonant Condition

A frequency shift of a Raman peak is observed in 2H-MoS 2 , when the exciting laser frequency ω i is tuned across the A and B excitonic levels. The frequency shift decreases as ω i increases. It ca...

Structural Phase Transition and Metallic Behavior in Misfit Layered (Bi,Pb)-Sr-Co-O System.

The crystal structure of Bi2-xPbxSr2Co2Oy has been investigated by X-ray diffraction and electron diffraction analyses. In contrast to what has previously been considered a Bi2Sr2CaCu2O8-type structure, we found that this material has a misfit layer structure: two subcells with different periodicities are alternately stacked. We have studied the x dependence of the crystal structure and found a discontinuous phase transition at x 0.2, where only Bi-Sr-O layers show a drastic change in lattice constants. Pb doping induces metallic behavior, but the effect of the structural phase transition is less clearly observed, which indicates that the electronic properties are mainly dominated by CoO2 layers.

SPIN-PEIERLS AND ANTIFERROMAGNETIC PHASES IN CU1-XZNXGEO3 : A NEUTRON-SCATTERING STUDY

Comprehensive neutron-scattering studies were carried out on a series of high-quality single crystals of Cu

Neutron-Scattering Study of Magnetism in Single-Crystal Cu1-xZnxGeO3

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Antiferromagnetic long-range order caused by nonmagnetic impurities; magnetization of single-crystal Cu1−xZnxGeO3

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Superconductivity of Bi2Sr2Can−1CunOy (n=2, 3, 4, and 5) thin films prepared in situ by molecular‐beam epitaxy technique

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