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Temperature dependence of the velocity Vs and the attenuation of the ultrasonic waves are measured to investigate the relation between the spin type of magnetic order and lattice instability of the low-temperature tetragonal phase in La2-xSrxCuO4 (x ∼ 1/8). In the field above 8 T along the [0 1 0]o direction of the orthorhombic notation, a significant increase of Vs in the c44 mode is observed below ∼15 K where spin-flop occurs. This gigantic increase of Vs suggests that the structural transformation from the orthorhombic to the low-temperature tetragonal phase is induced by the spin-flop. © 2000 Elsevier Science B.V. All rights reserved.

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

Carrier-doping effects on electronic correlations on the verge of the Mott transition in La1-xSrxTiO3 have been investigated by Ti-47/49 and La-139 NMR. In antiferromagnetic (AF) insulator of LaTiO3 with TN = 140 K, we observed zero-field Ti NMR and determine the hyperfine field of 91.4 kOe for Ti nuclei. The increases of nuclear spin-lattice relaxation rates (T-1)(-1) of La and Ti show that effective carrier mass is enhanced critically as the Mott transition boundary is approached from the metallic side. We have no evidence for a prominent increase of AF spin fluctuations at q similar to Q near the Mott transition boundary. Together with the temperature dependence of T-1 (The Korringa relations of T1T=const are observed for La and Ti) in the metallic state, we conclude that the AF spin fluctuations of Ti-3d spins due to the interatomic electronic correlations is not important, but single-site (intraband) electronic correlations play an important role in driving the metal-insulator transition in La1-xSrxTiO3, as opposed to the case of high-T-c cuprates. [S0163-1829(99)13415-5].

The superconducting transition in the electrical resistivity has been examined for La2-xSrxCuO4 (x ∼ 0.12) single crystals in magnetic fields. The broadening of the transition width in high fields is small compared to the case of the optimum doping (x ∼ 0.15) and the transition curve as a function of the temperature in each magnetic field shifts to lower temperature in almost parallel with applying magnetic field similar to the case of conventional superconductors. These results indicate that the superconducting fluctuation is weakened and that the coherence length in the CuO2plane becomes much longer around x=0.12. The measurement results are discussed in relation to the appearance of long-range magnetic order. © 1999 The American Physical Society.

Breakdown of non-conductive state of Corbino discs at integer filling factors of Landau levels at high source-drain voltages has been measured for samples fabricated from GaAs/Al0.3Ga0.7As heterostructures. Critical breakdown electric fields at the filling factors of 1, 2, 4 and 6 are in agreement with the critical breakdown Hall electric fields in the quantized Hall plateaus with these quantum numbers measured in butterfly-type Hall bars. © 1998 Elsevier Science B.V. All rights reserved.

Magnetic superlattice peaks are observed in single-crystal neutron-diffraction measurements on orthorhombic (Formula presented) at reciprocal points of (1/2±ε,1/2,0) and (1/2,1/2±ε,0) in the tetragonal notation where (Formula presented)0.126(Formula presented)0.003. The La NMR measurement reveals a broadening of the field-swept spectrum below (Formula presented)45 K corresponding to the existence of magnetic order. The remarkable softening of longitudinal sound waves along [110] is observed in the same crystal. The features observed in the neutron diffraction, NMR, and ultrasonic measurements suggest that the dynamical incommensurate spin correlation is pinned by a lattice instability toward the low-temperature tetragonal phase. © 1998 The American Physical Society.

We report (Formula presented) measurements on a single crystal of superconducting (Formula presented) where (Formula presented) is bis(ethylenedithiotetrathiafulvalene), (Formula presented) The temperature dependence of the spectrum has revealed that two phase transitions occur on cooling; first at (Formula presented) where a single resonance peak splits into two subpeaks, and second at (Formula presented) where the subpeaks disappear after the broadening at 25 K. The former associated by temperature hysterisis is a first-order phase transition and the splitting width follows (Formula presented) dependence. This splitting, which is so sensitive to the field orientation due to (Formula presented) is found to be caused by the quadrupole interaction. The spin-lattice relaxation rate (Formula presented) is strongly elongated by three orders of magnitude with decreasing temperature from 200 K, followed by the maximum around 40 K. This dramatic effect is interpreted by the Bloembergen-Purcell-Pound model applied to the quadrupole interaction. Discussions are made from the viewpoint of the dynamics of noncentrosymmetric tetrahedral molecule (Formula presented) at (Formula presented) the uniform rotation might switch to the thermally activated hopping motion between preferable sites bonded to nitrogens of (Formula presented) legands and then the order-disorder transition might eventually occur at (Formula presented) to form an anion ordering. © 1998 The American Physical Society.

The effect of the external field on La-NMR spectra has been studied on La-based high-T-c cuprates La2-xSrxCuO4 (x approximate to 0.115) and La2-xBaxCuO4 (x = 0.125), where the magnetic ordering in Cu-3d spin exists at low temperature. In the magnetically ordered state, the broadening in the resonance line was observed, reflecting the hyperfine field at the La-site contributed by the Cu-3d spins. By applying a high magnetic field of 15 T, this broadening in La2-xSrxCuO4 showed a significant shrink, which is interpreted as the spin-flop in the canted-spin system with the Dzyaloshinski-Moriya interaction. A model is proposed to explain both this spin-flop and the previously-reported anomalous field dependence of the structural instability in this system.

Cu-NMR spectra and the nuclear spin-lattice relaxation rate T-1(-1) have been studied intensively on the bilayer type high-T-C cuprate La1.89Ca1.11Cu2O6+delta (La2126). The resonance line shift showed a monotonic decrease with lowering temperature in the normal state, indicating that this compound belongs to the lightly-doped region. The Curie-Weiss temperature dependence of (T1T)(-1) in the normal state shows that the pseudo spin-gap does nor always exist in the light-doped bilayer systems.

The end member of the T1-based high-T-c cuprate TIBa2YCu2O7 (Tl1212) with the zero nominal hole number has been synthesized and studied by Cu/Tl NMR. The existence of the antiferromagnetic ordering was demonstrated by the Zeeman-splitted zero-field Cu spectra. Static parameters at the Cu site such as the hyperfine field H-Cu=8.62 T and the quadrupolar frequency (63)v(Q)=20.44 MHz were found to be comparable to other high-T-c related antiferromagnets La2CuO4 and YBa2Cu3O6. The relaxation rate T-l(-1) of the Cu site of Tl1212 showed a significant deviation from the magnon theory, and was much smaller than La2CuO4 and YBa2Cu3O6. The scaling between the temperature dependence of Tl T-l(-1) and Cu T-l(-1), the ratio of which was consistently explained with the hyperfine coupling constants determined by the analysis of spectra, showed that the relaxation is dominated by the 3d spin fluctuation. A possible relation between the spin fluctuation in the antiferromagnetic phase and the superconductivity in the high-T-c phase is also stated.

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.

The non-magnetic impurity effect has been investigated by NMR on Zn-doped TlBa2CaCu2O7 + δ belonging to the over-doped region, where the reduction rate in Tc with Zn-doping was found to be approximately - 2.3 K/%, much smaller than La1.85Sr0.15CuO4 and YBa2Cu3O7. The temperature dependence of the Cu-NMR Knight shift was analyzed with the partially closed d-wave model proposed by Ishida et al. to find that the residual density of states at the Fermi level increases with the Zn-concentration. The ratio between the residual density of states and the reduction rate in Tc was found to be in accordance with the theoretical calculation in the unitarity limit by Miyake.

The anisotropy of the activation energy of the flux pinning in a La1.85Sr0.15CuO4 single crystal was investigated by ultrasonic measurements in various directions of wave vector k, polarization vector u and magnetic fields H. The large activation energy of U(0 K, 14 T) = 972 K and small field dependence alpha H--0.3 were obtained for H parallel to c-plane, when the flux motion is parallel to the c-axis where the intrinsic pinning mechanism due to the layered structure is effective. The elastic modulus of the flux-line lattice which moves parallel to the c-axis is proportional to H-2 cos (2) theta, and the value of U rapidly decreases with increasing tilt angle theta between H and the c-plane (U(theta = 10 degrees) similar to 300 K. U(theta = 30 degrees) similar to 75 K). These angular dependences of the elastic modulus and the activation energy can be explained on the basis of the intrinsic pinning mechanism and the three-dimensional stepwise flux-line structure.

The end member of the Tl-based high-(Formula presented) cuprate (Formula presented)(Formula presented)(Formula presented) (Tl1212) with the zero nominal hole number has been synthesized and studied by Cu/Tl NMR. The existence of the antiferromagnetic ordering was demonstrated by the Zeeman-splitted zero-field Cu spectra. Static parameters at the Cu site such as the hyperfine field (Formula presented)=8.62 T and the quadrupolar frequency (Formula presented)=20.44 MHz were found to be comparable to other high-(Formula presented) related antiferromagnets (Formula presented)(Formula presented) and (Formula presented)(Formula presented)(Formula presented). The relaxation rate (Formula presented) of the Cu site of Tl1212 showed a significant deviation from the magnon theory, and was much smaller than (Formula presented)(Formula presented) and (Formula presented)(Formula presented)(Formula presented). The scaling between the temperature dependence of Tl (Formula presented) and Cu (Formula presented), the ratio of which was consistently explained with the hyperfine coupling constants determined by the analysis of spectra, showed that the relaxation is dominated by the 3d spin fluctuation. A possible relation between the spin fluctuation in the antiferromagnetic phase and the superconductivity in the high-(Formula presented) phase is also stated. © 1996 The American Physical Society.

The flux line lattice (FLL) elasticity and its anisotropic pinning have been investigated in a single crystalline La1.85Sr0.15CuO4, by ultrasonic measurements under high magnetic fields. The depinning activation energies are deduced from measurements under various settings of the directions of wave vector k, polarization vector a and magnetic fields H as U-ac(0 K, 14 T) = 972 K for H perpendicular to c, u parallel to c, U-ab(0 K, 14 T) = 201 K for H perpendicular to c, u parallel to(cxH) and U-ca(0 K, 14 T) = 25 K for H parallel to c, u perpendicular to c. The magnetic field dependence of U are also deduced as U(ac)proportional to H--0.3 and U(ca)proportional to H--1.5. The angular dependence of U-ac is discussed on the basis of the intrinsic pinning mechanism.

Properties of the breakdown of the quantum Hall effect due to current have been measured in specially designed samples with the width ranging from 10 to 120 mum made from a Ga-As/AlGaAs heterostructure wafer at temperatures between 0.5 and 1.2 K in magnetic fields up to 23 T. Critical current in the onset of the breakdown is proportional to the sample width. The critical current density does not depend on temperature but depends on the Hall-plateau quantum number i for i = 1, 2 and 4 where R(H)(i)=h/ie2. Experimental results can be explained by production of dissipative carriers by inter-Landau-level transitions from the filled Landau level to the empty Landau level cuased by strong local electric fields in the extended states enhanced due to the localization.

Magnetic field dependence of the device-width-dependent breakdown current in the quantum Hall effect is measured in magnetic fields up to 23 T at 0.5 K for GaAs/AlGaAs Hall bars having a total length of 2900 mum, a source and drain-electrode width of 400 mum and different widths 10, 20 and 35 mum in its central 600 mum long part. Results are explained in terms of localization in Landau levels without edge-state transport.

The temperature dependence of La-139-NMR spectra has been studied on the copper oxide superconductor La2-xBaxCuO4 around x congruent-to 0.125, at which the superconductivity is anomalously suppressed. The significant broadening in resonance lines was observed below 35K, suggesting the antiferromagnetic phase transition of Cu 3d-spins. The analysis of the spectra has revealed that the internal field at La site is approximately 170 Oe, perpendicular to c-axis.

Zero-field spectra of the antiferromagnetic Cu-NMR have been observed on the Tl-based copper oxide TlBa2YCu2O7 (Tl1212). The internal field and the electric field gradient at Cu site have been found to be comparable to other antiferromagnetic phase of high-T(c) oxides. Hyperfine coupling constants of both Cu and Tl sites have been obtained through the analysis of Tl and Cu spectra.

All the electron-doped high-T(c) oxides discovered so far inevitably contain lanthanides, whose 4f-spin fluctuation hides all the NMR information on the superconductivity. The new copper oxide superconductor (La1-yYy)2-xCexCuO4 with T'-type structure, which is free from 4f-spins has been successfully synthesized. Obtained compounds showed a nearly zero electric field gradient(EFG) at Cu site, which demonstrates that the doped carrier is electronic.