4PO5-10 Unconventional Superconducting Characteristics in CuBa₂Ca₃Cu₄O_12+y Probed by Cu-NMR

Yo Tokunaga 1, Hisashi Kotegawa 1, Kenji Ishida 1, Yoshio Kitaoka 1, Kazuyasu Tokiwa 2, Akira Iyo 2, and Hideo Ihara 2. 1 Department of Physical Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan. 2 Electrotechnical laboratory, 1-1-4 Umezono, Tukuba, Ibaraki 305, Japan.

Presenting Author: Y. Tokunaga

We report Cu-NMR studies on multilayer high-T_c cuprate (Cu_0.6C_0.4)Ba₂Ca₃Cu₄O_12+y (Cu1234) with T_c=117 K. The Cu-Knight shift and the nuclear spin-lattice relaxation rate markedly decrease below T_c=117 K for the underdoped inner CuO₂ planes (IP), whereas for the overdoped outer ones (OP) they decrease moderately below T_c, but markedly below T_c2=60 K. The superconducting (SC) gap is shown to develop linearly between T_c=117 K and T_c2 = 60 K in the OP.

We propose that the SC state at the OP is induced below T_c via the interlayer Josephson coupling with the IP and T_c2 corresponds to a seeming SC transition temperature inherent to the overdoping level in the OP.

*4PO5-11 ¹³⁹La and ⁶³Cu NMR investigations of LSCO single crystals

M.-H. Julien 1,2 F. Borsa 1,2, P. Carretta 1, A. Rigamonti 1, M. Horvatic 3, C. Berthier 3, P. Kuhns 4, A.P. Reyes 4, W.G. Moulton 4, C.-T. Lin 5, A. Vietkin 6, and A. Revcolevschi 6. 1 Dpt. Physics and Unita INFM di Pavia, Italy. 2 Dpt. Physics and Astronomy, ISU, Ames Lab., Ames, IA, USA. 3 Grenoble High Magnetic Field Lab., France. 4 NHMFL Tallahassee, USA. 5 MPI Stuttgart, Germany. 6 Lab. Chimie des Solides Orsay, France.

Presenting Author: M.-H. Julien

We present ⁶³Cu, ¹³⁹La NMR and NQR results in underdoped La_2-xSr_xCuO₄ single crsytals. Measurements of the spin-lattice relaxation rate of ¹³⁹La (1/T1) reveal a dramatic slowing down of magnetic fluctuations [1]. At low temperature superconductivity coexists with frozen staggered Cu²⁺ moments. We also describe anomalous NMR and NQR spectra above the freezing temperature. These results are compared to those obtained by other NMR experiments and by other techniques in similar compounds. Some implications are highlighted.

[1] M.-H. Julien et al., Phys. Rev. Lett. 83, 604 (1999), cond-mat/9909351, and unpublished.

4PO5-12 ^63,65Cu NQR study of Zn and Ni doped YBa₂Cu₃O₇

K.S. Han 1, B.J. Mean 1, K.H. Lee 1, D.H. Kim 1, S.W. Seo 1, Moohee Lee 1, W.C. Lee 2, and J.S. Cho 3. 1 Dept. of Physics, Kon-Kuk University, Seoul 143-701, Korea. 2 Dept. of Physics, Sook-Myung Woomen's University, Seoul 140-742, Korea. 3 Dept. of Information Communications, Suwon Science College, Kyong-Ki 445-960, Korea.

Presenting Author: M. Lee

^63,65Cu nuclear quadrupole resonance (NQR) measurements have been performed on Zn and Ni doped YBa₂Cu₃O₇ (YBa₂Cu_3-xM_xO₇, M=Zn or Ni, x=0~0.09). Distinctive differences due to the nonmagnetic Zn and the magnetic Ni dopants substituted for coppers are compared microscopically based on the plane and the chain ^63,65Cu NQR data. Doping effects are observed in resonant frequencies and linewidths of spectra, and relaxation times as well as in superconducting transition temperatures. Both spin-lattice and spin-spin relaxation rates decrease for Zn doped YBCO whereas those increase for Ni doped YBCO. From the isotropic ratio of spin-lattice relaxation rate, a dominant relaxation mechanism is determined as a function concentration and discussed in conjunction with magnetic moments of the dopants.

4PO5-13 Cu-NQR study for the disappearance of superconductivity in R_1-xPr_xBa₂Cu₃O₇ (R=Y and Nd).

M. Matsumura, N. Kitauchi, T. Yokoyama, M. Horiike, and H. Yamagata, Dept. of Material Science, Faculty of Science, Kochi University, Kochi 780-8520, Japan

Presenting Author: M. Matsumura

In order to investigate the microscopic charged state for the disappearance of superconductivity in PrBa2Cu₃O₇, Cu-NQR spectrum has been observed over the whole range of x in the normal conducting and paramagnetic state in R_1-xPr_xBa₂Cu₃O₇ (R=Y and Nd). The NQR frequencies at the Cu(2) and Cu(1) sites do not almost change with increasing x, which is marked contrast to the systematic decrease of the Cu(2)-NQR frequency with the decrease of the doped holes in YBa₂Cu₃O_y and La_2-ySr_yCuO₄. Since the Cu(2)-NQR frequency is proportional to the electric field gradient at the Cu(2) nucleus produced by surrounding electric charges, the present results suggest that the doped holes in the CuO₂ plane in x=0 become localized with increasing x without substantial change of the charge distribution around Cu(2) site. The origin for the disappearance of superconductivity in PrBa₂Cu₃O₇ is ascribed to some mechanism not accompanying with charge transfer.

4PO5-14 ¹³⁹La and ⁶³Cu NQR in Zn-doped Lanthanum Cuprate

B.J. Suh 1, Z.H. Jang 2, F. Borsa 2, Y. Zhuo 3, and S.-I. Lee 3. 1 Department of Physics, The Catholic University of Korea, Korea. 2 Ames Laboratory and Department of Physics, Iowa State University. 3 Pohang Superconductivity Center, POSTECH, Korea.

Presenting Author: B.J. Suh

It is well known that the superconducting transition temperature T_c is dramatically suppressed by very small substitution of Zn for Cu in La_2-xSr_xCuO₄ high temperature superconducting cuprate. ¹³⁹La and ⁶³Cu NQR relaxation measurments have been performed on a series of La_1.87Sr_0.13Cu_1-yZn_yO₄ (y < 0.03) powder in order to investigate the effects of Zn-doping on the spin and/or hole dynamics in CuO₂ plane and hence on the superconductivity. At low temperature, ¹³⁹La NQR spin-lattice relaxation rate T1^-1 of Zn-doped sample exhibits a strong enhancement which is similar to the spin glass behavior observed in lightly hole doped La_2-xSr_xCuO₄. From the temperature dependence of ⁶³Cu T1^-1, we found that the apparent spin gap is suppressed as increasing Zn concentration. These anomalous magnetic properties of La_1.87Sr_0.13Cu_1-yZn_yO₄ are discussed in relation to NMR/NQR studies of other lanthanum based cuprates.

4PO5-15 Evidence for Ba-site occupation of Pr³⁺ in Y_1-xPr_xBa₂Cu₃O_7-d from Cu NQR

Arneil P. Reyes, Margie M. Abdelrazek, Philip L. Kuhns, and William G. Moulton, National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA.

Presenting Author: A.P. Reyes

^63,65Cu nuclear quadrupole resonance (NQR) at ambient temperatures has been performed to probe Ba-site occupation of Pr atoms in Y_1-xPr_xBa₂Cu₃O_7-d (0 £ x £ 1.0). Anomalous spectral peaks were observed. Qualitative comparisons with electric field gradient (EFG) simulations suggest that these extra peaks come from Pr³⁺ ions on the Ba site with a concomitant occupation of the anti-chain O(5)-site. The results also suggest that this peculiar lattice arrangement has an effect on EFG that is different and distinguishible from that produced by a random chain oxygen distribution such as those that occur in underdoped (oxygen-deficient) Y_1-xPr_xBa₂Cu₃O_7-d . We discuss the implications of these results to a theory of Dow that suggests that the depression of superconductivity in this system is due to pair-breaking from local Pr moments on the Ba site. [1]

[1] H.A. Blackstead, et al. Phys. Lett. A 207, 100, 1995.

4PO5-16 Effect of Doping on the Behaviour of Spin Susceptibility in Tl₂Ba₂CaCu₂O_8-d compounds: ⁶³Cu and ¹⁷O NMR studies

Alexander P. Gerashenko 1, Stanislav V. Verkhovskii 1, Yurii V. Piskunov 1, Konstantin N. Mikhalev 1, Andrey Yu. Yakubovskii 2, and Arlette Trokiner 3. 1 Institute of Metal Physics, Russian Academy of Sciences, Ekaterinburg, Russia. 2 Russian Research Center "Kurchatov Institute", Moscow, Russia. 3 Ecole Superieure de Physique et Chimie Industrielles, Paris, France.

Presenting Author: A.P. Gerashenko

NMR line shifts, spin-lattice relaxation rates of ⁶³Cu and ¹⁷O and spin-echo decay rate ⁶³T₂^-1 were measured in normal and superconducting states of Tl₂Ba₂CaCu₂O_8-d with different hole concentration (T_c=102K, 112K and 104K). The magnetic hyperfine fields on the atoms of copper and oxygen in the CuO₂ layer were estimated using the temperature dependence of the Knight shift. The temperature dependences of magnetic correlation length and characteristic energy of antiferromagnetic spin fluctuations were obtained using the ^63.17T₁^-1 and ⁶³T₂^-1 data. Crossover in temperature between different regimes of spin fluctuations is considered and transition from quantum critical regime into the regime of nearly anti-ferromagnetic Fermi liquid was revealed in going to overdoped state of cuprate. Corresponding critical temperatures fixing the change of the regime of magnetic fluctuations was determined. It was found that the spin gap at q» 0 and q» {p /a; p /a} is decreased with increase of hole concentration, but the gap-like behaviour of spin susceptibility is still retained in the overdoped state of cuprate (T_c=104K).

4PO5-17 ⁶³Cu NMR Evidence for Enhanced Antiferromagnetic Correlations around Zn Impurities in YBa₂Cu₃O_6.7

M.-H. Julien 1, T. Feher 1,2, M. Horvatic 1, O.N. Bakharev 1,3, C. Berthier 1,4, P. Segransan 4, G. Collin 5, and J.-F. Marucco 6. 1 Grenoble High Magnetic Field Lab., France. 2 Phys. Institute, Technical University, Budapest, Hungary. 3 Magn. Res. Lab., Kazan State University, Russia. 4 Lab. Spectrometrie Physique. Grenoble, France. 5 LLB Saclay, France. 6 LCNS Orsay, France.

Presenting Author: M.-H. Julien

Doping the high-T_c superconductor YBa₂Cu₃O_6.7 with 1.5 % of non-magnetic Zn impurities in CuO₂ planes is shown to produce a considerable broadening of ⁶³Cu NMR spectra, as well as an increase of low-energy magnetic fluctuations detected in ⁶³Cu spin-lattice relaxation measurements.

Analysis of Cu NMR lineshapes for both field orientations H½ ½ c-axis and H ab-plane, demonstrates that these effects are due to the development of staggered magnetic moments on many Cu sites around each Zn. Furthermore, this analysis provides quantitative information on the response to impurity doping: we find that the typical size of each staggered "island" is given by the magnetic correlation length of the pure system, and that the "Zn-induced moment" in the bulk susceptibility is a composite object mainly built by the sum of all staggered moments.

These conclusions, which are essentially model-independent, are interpreted as an enhancement of antiferromagnetic correlations around Zn impurities. We discuss the implications of these results for our understanding of spin and charge correlations in these materials.

4PO5-18 Counterdoping Effect of Pr in YBCO measured by ¹⁷O NMR

W.A. MacFarlane 1, J. Bobroff 1, P. Mendels 1, L. Cyrot 1, H. Alloul 1, N. Blanchard 1, G. Collin 2, and J.-F. Marucco 3. 1 LPS Bât. 510, Universite Paris Sud, UMR8502 CNRS, Orsay 91405, France. 2 LLB, CEN Saclay, CEA-CNRS, Gif-sur-Yvette 91191, France. 3 LCNS, Université Paris Sud, Orsay 91405, France.

Presenting Author: W.A. MacFarlane

Comparison of the the planar ¹⁷O NMR shift in Pr substituted YBCO with that of pure underdoped YBCO allows us to conclude that Pr reduces the concentration of mobile holes in the plane, and in the dilute regime to quantify the rate of counterdoping. The rate we find is insufficient to explain the observed reduction of T_c. We conclude from the temperature dependent magnetic broadening of the ¹⁷O NMR that the Pr magnetic moment is exchange-coupled to the CuO₂ planes where it induces a long range spin polarization. This result is compared to analogous measurements in Ni and Zn substituted YBCO. The scattering associated with the existence of such a coupling provides another T_c reduction mechanism. We find a qualitatively different behaviour in the oxygen depleted Pr/YBCO_6.6, i.e. the suppression of T_c is nearly the same, but the counterdoping is weaker. This difference is likely a consequence of weaker coupling of Pr to the planes in combination with the stronger response of the underdoped CuO₂ planes to defects.