A. Maeda

The optical study of the doping effect in single-crystal Bi2Sr2(Ca, A)Cu2O8+x (A=YorNd)

Abstract The reflectivity of single-crystal Bi 2 Sr 2 (Ca, A)Cu 2 O 8+ x (A=Y or Nd) was measured and transformed to the optical conduc tivity through the Kramers-Kronig relation. A broad peak is observed in the mid-infrared region in the conductivity of the semiconducting samples, and the position of the peak shifts to O eV with increasing doped-carrier concentration. For the superconducting sample, the peak is located near O eV where a Drude model is approximately valid in the mid-infrared region, while a Lorentz model is appropriate for the mid-infrared spectra of the other samples. The conductivity was fitted by two Lorentz oscillators and one Drude term, and the electronic states of the high- T c cuprates were discussed in terms of the obtained fitting parameters.

Evidence for insulating behavior in the electric conduction of (NH3)K3C60 systems

Microwave study using the cavity perturbation technique revealed that the conductivity of the antiferromagnet (NH(3))K(3-x)Rb(x)C(60) at 200 K is already 3-4 orders of magnitude smaller than those of superconductors, K(3)C(60) and (NH(3))(x)NaRb(2)C(60), and that the antiferromagnetic compounds are insulators below 250 K without metal-insulator transitions. The striking difference in the magnitude of the conductivity between these materials strongly suggests that the Mott-Hubbard transition in the ammoniated alkali fullerides is driven by a reduction of lattice symmetry from face-centered-cubic to face-centered-orthorhombic, rather than by the magnetic ordering.

Microwave and millimeter wave spectroscopy in the slightly hole-doped ladders of Sr14Cu24O41

We have measured the temperature and frequency dependence of the microwave and millimeter wave conductivity σ1(T,ω) along both the ladder (c-axis) and the leg (a-axis) directions in Sr14Cu24O41. Below a temperature T* ( ~ 170 K), we observed a stronger frequency dependence in σ1c(T,ω) than that in σ1a(T,ω), forming a small resonance peak developed between 30 GHz and 100 GHz. We also observed nonlinear dc conduction along the c-axis at rather low electric fields below T*. These results suggest some collective excitation contributes to the c-axis charge dynamics of the slightly hole-doped ladders of Sr14Cu24O41 below T*.

Comparative study of macroscopic quantum tunneling in Bi2Sr2CaCu2Oy intrinsic Josephson junctions with different device structures

We investigated macroscopic quantum tunneling (MQT) of Bi

Electronic state of NbSe2 investigated by STM/STS

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Irradiation effects on MgB2 bulk samples and formation of columnar defects in high-Tc superconductor

Sr

Terahertz conductivity measurement of FeSe0.5Te0.5 and Co-doped BaFe2As2 thin films

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Gigantic optical Stark effect and ultrafast relaxation of excitons in single-walled carbon nanotubes

CaCu

Ultrafast Optical Responses in a One-Dimensional Mott Insulator of a Br-Bridged Ni Compound

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Sliding conduction by the quasi-one-dimensional charge-ordered state in Sr 14 − x Ca x Cu 24 O 41

O