後藤 貴行

翻訳「NMRでインチキワインを嗅ぎ分ける」 http://pub.maruzen.co.jp/book_magazine/magazine/parity-back/parity1999/1999_10/910_cont.html http://pub.maruzen.co.jp/book_magazine/magazine/parity-back/parity1999/1999_10/910_person.html

NMR study on three types of high-T_C cuprates TlBa_2CaCu_2O_<7+δ> (Tl1212), La_<2-x>Ba_xCuO_4 (LBCO) and (La_<1-y>Y_y)_<2-x>Ce_xCuO_4 (LYCCO) is reported. First the Knight shift in the superconducting state was investigated for the Zn-substituted TlBa_2Ca(Cu_<1-z>Zn_z)_2O_<7+δ>, which belongs to the over-doped region. The temperature dependence of the Knight shift was successfully explained in terms of the partially closed d-wave model proposed by Kitaoka et al. The reduction in T_C by Zn-substitution was also consistent with Miyake's theoretical calculation on the potential scattering of the unitarity limit in the d-wave superconductors. Next, the impurity effect on the anomalous suppression of the superconductivity in La_<2-x>Ba_xCuO_4 (LBCO) around x&cong;1/8 was investigated by La-NMR and ultrasonic measurements. The transition temperatures of the magnetic order and of the structural phase transformation in Zn^<2+> and Ce^<4+>-doped LBCO have shown that the main and direct force to the suppression in the superconductivity is the magnetic ordering, and that the role of the structural phase transformation is the enhancement of the suppression. Lastly, the new electron doped cuprate free from 4f-spins has been synthesized and studied by NMR. Observed spectra of ^<63/65>Cu without quadrupolar splitting similar to other conventional electron-doped cuprates indicate that the doped carrier in this system is electron like.

Integer and fractional quantum Hall effects are interesting phenomena in two-dimensional electron systems (2DES) in strong magnetic fields. In this paper, breakdown of the integer quantum Hall effect (IQHE) at odd integer filling factors at 100 mK and temperature dependence of the fractional quantum Hall effect (FQHE) around the filling facor ν=1/2 at temperatures between 100 mK and 1000 mK in magnetic fields up to 25 T are measured for the 2DES in two AlGaAs/GaAs heterostructures. The results in the IQHE measurements are compared with results at the even filling factors and derive the effective g-factor of about 10 in this system. The results in the FQHE measurements at ν=1/2 shows a logarithmic temperature dependence of the conductivity which is expected in a weakly localized Fermion system in zero magnetic fields.

Temperature dependence of the sound velocity of La_<1.85>Sr_<0.15>CuO_4 single crystals has been measured in high magnetic fields up to 23 T. The anisotropy of the activation energy of the flux pinning is evaluated from the analysis of the excess elastic modulus due to the flux line lattice. The large activation energy of U(0 K, 14 T)=972 K and the small field dependence ∝H^<-0.3> are obtained for H//c-plane where the intrinsic pinning mechanism due to the layered structure is effective. The value of U rapidly decreases with increasing the tilt angle θ between H and the c-plane. The angular dependence of U is explained on the basis of the three-dimensional stepwise-flux-line structure. Moreover, elastic anomalies have been observed at T_c and near irreversibility line. The upper critical field is evaluated from the anomaly at T_c and origin of the elastic anomaly near irreversibility line is discussed.