4PO8-10 Muon Spectroscopy of Eu_2-zCe_zSr₂Cu₂RuO₁₀

Dale R. Harshman 1,2, H.A. Blackstead 1, J.D. Dow 3, I. Felner 4, D.B. Pulling 1, W.J. Kossler 5, A.J. Greer 6, C.E. Stronach 7, E. Koster 8, and B. Hitti 9. 1 Physics Department, University of Notre Dame, Notre Dame, IN 46556 USA. 2 Physikon Research, Inc., P.O. Box 2421 Blaine, WA 98231 USA. 3 Physics Department, Arizona State University, Tempe, AZ 85287-1504 USA. 4 Raccah Institute of Physics, The Hebrew University, Jerusalem, Israel 91904. 5 Physics Department, College of William and Mary, Williamsburg, VA 23185 USA. 6 Physics Department, Gonzaga University, Spokane, WA 99258 USA. 7 Physics Department, Virginia State University, Petersburg, VA 23806 USA. 8 Physics Department, University of British Columbia, Vancouver, B.C. Canada V6T 1Z1. 9 TRIUMF, Vancouver, B.C. Canada V6T 2A3.

Presenting Author: D.R. Harshman

Muon spin rotation (m SR) measurements of superconducting Eu_2-zCe_zSr₂Cu₂RuO₁₀ (T_c~43 K) identify two distinct stopping sites, one that we associate with the RuO₂ layers and another with the SrO layers. The RuO₂ and CuO₂ layers order at ~190 K and ~100 K, respectively. At low temperatures (T < ~20 K) the local field sensed at a Ru-site is ~900 G, with a corresponding exponential relaxation rate of about ~30 (m s)-1. Below ~120 K, the SrO signal shows a dramatic negative shift in the local field --- concomitant with a relaxation rate that increases with decreasing temperature. Direct modeling of the dipole fields produced by antiferromagnetically ordered Cu spins indicate that they are the origin of this local field. Since the Ru and the Cu spins are both ordered at and above T_c, it is extremely unlikely that the primary hole condensate resides in either the RuO₂ or the CuO₂ layers. Instead, the SrO layers must be the loci of the primary superconductivity.

4PO8-11 Impurity Scattering in p-wave superconductivity: Sr₂RuO₄

Evgenii Puchkaryov and Kazumi Maki, Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089-0484, USA

Presenting Author: K. Maki

Growing evidence indicates the newly discovered superconductivity in Sr₂RuO₄ is of triplet p-wave. For example, the Knight shift of ¹⁷O in NMR shows clearly the spin triplet pair is involved [1]. Here we review our result on the effect of impurity scattering in p-wave superconductors where the scattering is assumed in the unitarity limit. The superconducting order parameter is taken as D ^k d^k1 ± ik²), where d^is the spin vector (d½ ½ c), and k is the quasi-particle momentum within the a-b plane. The most remarkable property is that the impurity scattering produces an island of the density of states near E=0 (i.e. on the Fermi surface), which can be detected by both the thermodynamic and transport measurements. Comparison with the recent specific heat data [2] indicates that the present model is applicable to less pure samples with T_c £ 1.2 K, but the strong deviation from this model is observed in the pure samples. A promising extension of the present model is the three-band model with three different order parameters.

[1] K. Ishida et al., Nature 396 p658 (1998).

[2] S. Nishizaki et al., Proceedings MOS’99.

4PO8-12 Structure Investigations into LaGaO₃ – NdGaO₃ system

A. Matkovski 1,2, L. Vasylechko 2,3, M. Berkowski 4, D. Savytskii 2,3, and M.Vakiv 3. 1 IF HPS, 16A Rejtana St., Rzeszow 35310, Poland. 2 Semicond. Electronics Dept. of State University "Lviv Politechnic", Lviv 79646, Ukraine. 3 R&D Institute for Materials of SRC "CARAT", 202 Stryjska St., Lviv 79031, Ukraine. 4 Institute of Physics Polish Academy of Science, Al. Lotnikow 32/46, 02-668 Warsaw, Poland.

Presenting Author: A. Matkovski

The LaGaO₃-NdGaO₃ system was investigated by means of X-ray and EPM analysis. The samples - La_1-xNd_xGaO₃ single crystals (x=0, 0.07, 0.12, 0.17, 0.20, 0.27, 0.32, 0.37, 0.44, 0.53, 0.62 and 0.79) were grown by Czochralski method. All crystals possess a GdFeO₃-type perovskite-like structure (sp. gr. Pbnm, Z=4). The lattice constants a decreases from 5.52266(6) to 5.46754(7)Å and c from 7.7713(1) to 7.74241(9)Å, whereas b increases from 5.49047(7) to 5.49118(6)Å with increasing Nd content. At Nd concentration x = 0.32, when the crystal adopts the pseudotetragonal symmetry, the perovskite-like cell parameter is equal to ap = 3.882 Å that implies zero mismatch with YBCO b lattice constant. The phase transition may not induce roughening of the substrate surface at all because it occurs at the temperature (810° C in La_0.68Nd_0.32GaO₃) above the deposition temperature of YBCO films. The first order phase transition does not occur in La_1-xNd_xGaO₃ solid solution crystals at Nd concentration x > 0.7. It enables one to grow single crystals without twins. The most suitable for epitaxial film deposition are La_1-xNd_xGaO₃ solid solutions with x in the range from 0.32 to 1, because in this region the formation of surface roughness can be avoided. Their lattice parameter a_p may be changed in the range from 3.882 to 3.863 Å, thus allowing to control the internal stress by choosing the appropriate substrate/film combination.

4PO8-13 Observation of a linear temperature dependence of the critical current density for a Ba_0.63K_0.37BiO₃ single crystal

Hyun-Tak Kim 1, Kwang-Yong Kang 1, Bong-Jun Kim 2, Y.C. Kim 2, W. Schmidbauer 3, and J.W. Hodby 3. 1 Telecom. Basic Research Lab., ETRI, Taejon 305-350, Korea. 2 Department of Physics, Pusan National University, Pusan 609-735, Korea. 3 Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, Great Britain.

Presenting Author: H.-T. Kim

For a Ba_0.63K_0.37BiO₃ single crystal with T_c=30.5 K, D T_c=2 K (defined from T_c to 80% of ZFC susceptibility), H_c1» 750 Oe at 5 K, and dimensions 3x3x1 mm³, the temperature and field dependences of residual magnetization have been measured within 5-22.5 K in magnetic fields up to 6 Tesla. It is shown that the critical current density reaches J_c(0)» 1.0 x 10⁵ A/cm² for a zero field at 5 K. A linear temperature dependence of J_c(T) and a peak similar to "peak effect" in magnetization hysteresis curves were observed; these are new findings for the Ba_1-xK_xBiO₃(BKBO)superconductor. The linear temperature dependence of J_c(T) is different from the exponential temperature dependence or the power-law relation for High-T_c superconductors including the BKBO superconductor. The cause of the peak is not yet clearly revealed although it is similar to the peak effect.

4PO8-14 Ultrasonic investigation of structural instability in superconducting Ba(1-x)K(x)BiO3 single crystals

S. Zherlitsyn 1, B. Luthi 2, V. Gusakov 3, B. Wolf 2, D. Wichert 2, G. Bruls 2, S. Barilo 3, S. Shiryaev 3, C. Escribe-Filippini 4, and J. Tholence 4. 1 Institute for Low Temperature Physics & Engineering, 310164 Kharkov, Ukraine. 2 Physikalishes Institut, Universitadt Frankfurt, D-60054 Frankfurt, Germany. 3 Institute of Solid State & Semiconductor Physics, 220072 Minsk, Belarus. 4 Laboratoire d’Etudes des Proprietes Electroniques des Solides, CNRS, 38042 Grenoble, France.

Presenting Author: V.E. Gusakov

We report results of the ultrasonic investigation of Ba_1-xK_xBiO₃ single crystals for two potassium concentration x=0.37 and x=0.47 in a wide temperature range including the normal and superconducting states. An instability of the crystal lattice that develops above the superconducting phase transition leads to a softening of both the transverse c44 and the longitudinal c11 modes at temperatures between 200 K and 50 K. In the case of Ba_0.63K_0.37BiO₃ a pronounced hysteresis was discovered We have offered theoretical model for the description of abnormal behavior of ultrasound in the Ba_1-xK_xBiO₃ single crystals. It is shown that the dynamics of the BiO₆ octahedra in double well potential is responsible for the abnormal behavior of ultrasonic wave velocity. The interplay of abnormal lattice properties and superconductivity for Ba_1-xK_xBiO₃ superconductor is discussed.

4PO8-15 Temperature dependence of the low frequency phonon spectra in Ba_1-xK_xBiO₃

Yu.G. Pashkevich 1, V.P. Gnezdilov 2, V.V. Eremenko 2, P. Lemmens 3, M. Grove 3, G. Güntherodt 3, S.V. Shiryaev 4, S.N. Barilo 4, and A.G. Soldatov 4. 1 A.A. Galkin Donetsk Phystech NASU, 340114 Donetsk, Ukraine. 2 B.I. Verkin Inst. for Low Temp. Physics NASU, 310164 Kharkov, Ukraine. 3 II. Physikalisches Institut, RWTH Aachen, 52056 Aachen, Germany. 4 Inst. of Sol. St. and Semiconductor Physics, NAS 220072 Minsk, Belarus.

Presenting Author: Yu.G. Pashkevich

High quality single crystals of Ba_1-xK_xBiO₃ (x=0; 0.15, 0.2, 0.4, 0.5) have been investigated by Raman light scattering in the 10-300 K temperature range. The SQUID measurements have shown the onset of superconductivity at 30 K and 25 K for the samples with x=0.4 and x=0.5, respectively. The spectra of BaBiO₃ do not demonstrate any visible change upon cooling which is inconsistent with the well-known phase diagram [1]. There is a difference in the spectra for frequencies below 400 cm-1 comparing nonsuperconducting and superconducting samples. A common feature for all samples is the existence of a phonon line at 50cm_-1. The intensity of this line changes upon potassium content. According to neutron scattering data [2] one can assign it to the lowest breathing distortion phonon mode from the (0.5,0,5,0.5) point of the perovskite Brillouin zone. In the x=0.4 sample the intensity of this line depends nonmonotonically on temperature with a conspicuous hysteresis for the up and down temperature run in between 10 K -200 K. In the same temperature region a lattice instability with a strong softening of elastic moduli was observed for a sample with x=0.37 by ultrasonic measurements [3].

[1] S. Pey et al, Phys Rev. B 41, 4156 (1990).

[2] M. Braden et al, Journ. of Superconduct. 8, 595 (1995).

[3] S. Zherlitsyn et al, (private communications).

4PO8-16 EPR study of Ba_1-xK_xBiO₃ and BaPb_yBi_1-yO₃ system

A. Yu. Yakubovsky 1, S.V. Gudenko 1, A.I. Golovashkin 2, and A.P. Rusakov 3. 1 Russian Center Kurchatov Institute, Moscow, Russia. 2 P.N.Lebedev Physical Institute RAS, Moscow, Russia. 3 Moscow Steel and Alloys Institute, Moscow, Russia.

Presenting Author: A.Yu. Yakubovsky

EPR spectra of Ba_1-xK_xBiO₃ (BKBO) and BaPb_yBi_1-yO₃ (BPBO) samples were studied in wide ranges of doping levels and temperatures. Besides the signals with g»2.1 and g»4.2 existing in all the compositions [1] the wide EPR lines with intermediate g-factor were also found. The temperature evolution of these signals as well as the influence of technological conditions of sample preparation were investigated. The comparison with the similar EPR lines reported in La_2-xSr_xCuO₄ [2] and YBa₂Cu₃O_6+x [3] was carried out. From our studies of Cu-free samples the decisive role of oxygen ions in the formation of the observed EPR signals is evident. The results indicate the possibility for existence of oxygen ions with different effective charges, i.e. the presence of charge density wave in oxygen sublattice in addition to charge ordering in the metal one.

[1] A. Yu. Yakubovsky et al. JETP 88 (1999) 732.

[2] B.I. Kochelaev et al. Phys.Rev.Lett. 79 (1997) 4274.

[3] R. Eremina et al. Physica B (to be published).

4PO8-17 EPR study of BKBO and BPBO systems

Andrey Yu. Yakubovsky 1, Stanislav V. Gudenko 1, Aleksander I. Golovashkin 2, and Alexander P. Rusakov 3. 1 Russian Research Center "Kurchatov Institute", Moscow, 123182, Russia. 2 P.N.Lebedev Physical Institute, Moscow, 117924, Russia. 3 Moscow Steel and Alloys Institute, Moscow, 117049, Russia.

Presenting Author: A.Yu. Yakubovsky

EPR spectra of BaKBiO (BKBO) and BaPbBiO (BPBO) samples were studied in wide ranges of doping levels and temperatues. Besides the signals with g=2.1 and g=4.2 existing in all compositions [1] the wide EPR lines with intermediate g-factor were also found. The temperature evolution of these signals as well as the influence of technological conditions of sample preparation were investigated. The comparision with the similar EPR lines reported in LaSrCuO [2] and YBaCuO [3] was carried out. From our studies of Cu-free samples the decisive role of oxygen ions in the formation of the observed EPR signals is evident. The results indicate the possibility for existance of oxygen ions with different effective charges, i.e. the presence of charge density wave in oxygen sublattice in addition to charge ordering in the metal one.

[1] A.Yu. Yakubovsky et al. JETP 88 (1999) 732.

[2] B.I. Kochelaev et al. Phys. Rev. Lett. 79 (1997) 4274.

[3] R.Eremina et al. Physica B (to be published).

4PO8-18 Ordered perovskite non-superconducting oxides KBa_m-1Bi_m+nO_y

L.A. Klinkova 1, V.I. Nikolaichik 2, N.V. Barkovskii 1, and V.K. Fedotov 1. 1 Institute of Solid State Physics of the Russian Academy of Sciences, Chernogolovka, Moscow District, 142432 Russia. 2 Institute of Microelectronics Technology of the Russian Academy of Sciences, Chernogolovka, Moscow District, 142432 Russia.

Presenting Author: L.A. Klinkova

Recently we have put forward the hypothesis for two-phase fine-domain nature of current KBaBiO superconductors that results to the crystallographic structure of the superconductors being described as a solid solution one with shared positions of potassium and barium ions. Investigations of phase equilibrium in the K-Ba-Bi-O system to solve the inhomogeneity problem have resulted in finding six perovskite non-superconductiong oxides KBa_m-1Bi_m+nO_y. The presence of supercell spots in peculiar electron diffraction patterns suggests ordered arrangement of potassium and barium ions of two-dimensional type in certain of KBa_m-1Bi_m+nO_y oxides and three-dimensional one in the others.