ORAL SESSION 2C2: Cuprate-Based Materials

Tuesday, Feb. 22, 10:15 a.m. – 12:30 p.m., Room 302A (GRB)

Chairs: M. Alario-Franco (U Complutense de Madrid), M.B. Maple (U California-San Diego)

2C2.1 High pressure Synthesis on the Pr-Cuprate Superconductors

Z.X. Zhao, G.C. Che, and K.Q. Li, National Laboratory for Superconductivity, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China

Presenting Author: Z.X. Zhao

In this report, the synthesis and properties of Pr-system will be discussed.

The main contents are:

1. Pr-123, and its metallic state and superconductivity;

2. Ca-doped Pr-123 with T_c up to 115K, and related properties;

3. A Cu-based 1212 system with Pr and oxyanion group, and its superconductivity. A relation of T_c to a kind of ordering induced by a treatment and ionic radii of rare earth will be discussed.

2C2.2 High Pressure Synthesis of Copper-rich Perovskites from Single Phase Precursors

Douglas A. Vander Griend 1, Antione Maignan 1, and Kenneth R. Poeppelmeier 1, Hiroki Toganoh 2, Masaki Azuma 2, and Mikio Takano 2. 1 Department of Chemistry and the Science and Technology Center for Superconductivity, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113. 2 Institute for Chemical Research, Kyoto University, Uji, Kyoto-Fu 611, Japan.

Presenting Author: K.R. Poeppelmeier

Over seventy new copper-rich ABO₃ type compounds such as La₄Cu₃MoO₁₂ and La₃Cu₂VO₉ crystallize in the rare-earth hexagonal structure at ambient pressure. The Cu^II cations partially occupy a hexagonal lattice which leads to trigonal clusters of anti-ferromagnetic spin interactions similar to a kagome’ lattice. At 60,000 bar and 1200 ° C those with larger lanthanides transform to layered perovskites, and two dimensional antiferromagnetic ordering of the cuprate layers occurs above 200 K for the molybdates. Aliovalent substitutions elucidate the effect of cation size on the relative stability of the phases. The electronic and magnetic properties of the various materials can now be modified by doping charge carriers into the lattice.

2C2.3 New tailored cuprates grown by pulsed laser deposition.

Bernard Mercey 1, Trong-Duc Doan 1, Philippe Lecoeur 1, Wilfrid Prellier 1, Jean Francois Hamet 1, Paul A. Salvador 2, Bernard Raveau 1. 1 Laboratoire CRISMAT-ISMRA, UMR CNRS 6508, 14050 Caen France. 2 Department of Materials Sciences and Engineering, Carnegie Mellon University, Pittsburgh, USA.

Presenting Author: B. Mercey

Pulsed laser deposition has been shown to be a powerful method for the growth of oxide thin films, including metastable phases and superlattices.

Results dealing with the growth of artificially designed cuprates will be presented. The guideline of this work is the doping of the infinite layer structure like CaCuO₂ or SrCuO₂ to induce a superconducting behavior by introducing an appropriate "charges réservoir". Since a definition of the best "charge reservoir" does not exist, various insulator or conductor perovskite-like blocks were examined. These blocks are different from those currently used in the standard superconducting bulk materials such as mercury, thallium or bismuth phases.

The structural and physical properties of the superlattices grown using these various blocks will be presented. From these results, the difference in behavior between CaCuO₂ and SrCuO₂ is clearly evidenced. The latter is easily grown on perovskite-like materials but the possibility of extra-oxygen incorporation makes this material less suitable for understanding the doping mechanism. On the contrary, CaCuO₂ is difficult to incorporate into different superlattices, since the difficulty of incorporating extra-oxygen makes the growth of this material less flexible.

2C2.4 Experimental Investigations of Dynamics of Flux Creep in Cuprates

C. C. Almasan,¹ T. Stein,¹ G. A. Levin,¹ D. A. Gajewski,² and M. B. Maple^{2 1}Department of Physics, Kent State University, Kent, OH, 44240, USA. ²Department of Physics and Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, CA 92093, USA.

Presenting Author: C. C. Almasan

Transport as well as magnetic relaxation properties of the mixed state were studied on strongly underdoped Y_1-xPr_xBa₂Cu_3­­ O_7-d single crystals. We observed two correlated phenomena - a current independent coupling transition T* and a transition to quantum creep T_q. The dissipation is Ohmic above T* and non-Ohmic below T*. The distribution of transport current below the coupling transition is highly nonuniform, which facilitates quantum creep. A picture that arises from these observations is that the sample, at T < T*, is divided into two macroscopic regions: a layer near the primary face (where the current contacts are located) which carries most of the transport current, and the rest of the sample which remains mostly undisturbed by the current. Inside these layers the vortices are coupled, with the correlation length comparable to the thickness of the respective layer. On the other hand, these two macroscopic regions are decoupled from each other.

2C2.5 Joint Features of Pressure Effect and Specific Heat of RBa₂Cu₃O_x at distinct n_h Values

W.H. Fietz 1, U. Tutsch 1, K.P. Weiss 1, S.I. Schlachter 1, K. Grube 1, R. Hauff 1, Th. Wolf 1, B. Obst 1, P. Schweiss 2, and H. Wühl 1,3. 1 Forschungszentrum Karlsruhe, ITP, 76021 Karlsruhe, Germany. 2 Forschungszentrum Karlsruhe, IFP, 76021 Karlsruhe, Germany. 3 Universität Karlsruhe, IEKP, 76128 Karlsruhe, Germany.

Presenting Author: W.H. Fietz

In YBa₂Cu₃O_x, distinct features are found in the pressure dependence of the transition temperature, dT_c/dP, and in the jump of the specific heat, D C/T_c, at specific oxygen contents x_S and x_Q: dT_c/dP peaks at x_S and is zero at x_Q, whereas D C/T_c shows a maximum at x_Q and small values below x_S. Substituting Nd for Y and doping with Ca lead to a shift of both x_S and x_Q to larger and smaller oxygen contents, respectively. Since content and order of oxygen in these compounds are quite different this behavior seems to reflect an intrinsic property of the CuO₂ planes. Hence, using the hole concentration n_h in the CuO₂ planes at x_S and x_Q, the features coalesce in n_h(x_S) » 0.11 and n_h(x_Q) » 0.18, irrespective of the substitution and doping. A charge carrier content of n_h » 0.18 is usually attributed to the appearance of the pseudogap and n_h » 0.11 close to 1/8 may express a localization of charge carriers as predicted for stripe correlations. Our results of dT_c/dP may be explained by a reduction of the lattice parameters under pressure which changes the commensurability and thus the localization of charge carriers.

2C2.6 Superconducting gap D _s versus the number of CuO₂ layers n in Bi₂Sr₂Ca_n-1Cu_nO_2n+4+d , Tl₂Ba₂Ca_n-1Cu_nO_2n+4+d and HgBa₂Ca_n-1Cu_nO_2n+2+d

H. Schmidt 1, M.A. Lorenz 1, G. Müller 1, H. Piel 1, Kim Ki Uk 2, Ya.G. Ponomarev 2, N.Z. Timergaleev 2, K. Winzer 3, Ch. Janowitz 4, A. Krapf 4, R. Manzke 4, T.E. Os’kina 5, and Yu.D. Tretyakov 5. 1 Bergische Universität Wuppertal, Fachbereich Physik, Gaußstr. 20, D-42097 Wuppertal, Germany. 2 M.V. Lomonosov Moscow State University, Faculty of Physics, 119899 Moscow, Russia. 3 1. Physikalisches Institut der Universität Göttingen, Bunsenstr. 9, 37073 Göttingen, Germany. 4 Humboldt-Universität zu Berlin, Institut für Physik, Invalidenstr. 110, D-10115 Berlin, Germany. 5 M.V. Lomonosov Moscow State University, Faculty of Chemistry, 119899 Moscow, Russia.

Presenting Author: H. Schmidt

We have measured the superconducting gap D _s in optimally doped Bi₂Sr₂Ca_n-1Cu_nO_2n+4+d , Tl₂Ba₂Ca_n-1Cu_nO_2n+4+d and HgBa₂Ca_n-1Cu_nO_2n+2+d by Andreev and tunneling spectroscopy and by angle-resolved photoemisson spectroscopy. The low-temperature value of D _s was found to increase linearly with the number n of CuO₂ layers per unit cell (1 £ n £ 3). The variation of the critical temperature T_cmax with n does not obey this simple relation. For a given n the values of D _s at T = 4.2 K for the Tl- and Hg-families practically coincide but systematically exceed that in the Bi-family.

For Bi₂Sr_2-xLa_xCuO_6+d single crystals the superconducting gap D _s has been measured in the whole range of doping levels at temperatures 4.2 K £ T £ T_c. The value of D _s(4.2 K) was found to scale with the critical temperature T_c with the ratio 2D /kT_c = 12.5 ± 2, which significantly exceeds the reduced-gap ratios for the 2212- and 2223- phases. The closing of the gap D _s at T = T_c has been registered in the whole doping range. From the observation of a specific subharmonic gap structure due to an intrinsic multiple Andreev reflections effect (IMARE) in c-direction we conclude that the Bi₂Sr_2-xLa_xCuO_6+d crystals could be treated as superlattices of an S-N-S-N-… type. The possible influence of the proximity effect on the ratio 2D /kT_c is discussed on the basis of a theoretical model developed by Buzdin et al.

2C2.7 Magnets, Metals, and Mischief in Cobalt Analogs of the Superconducting Cuprates

R.J. Cava 1, K. Yamaura 1, S. Loureiro 1, N. McGlothlin 1, P. Khalifah 1, D. Young 1, Y. Liu 2, C. Felser 3, and Q. Huang 4. 1 Department of Chemistry and Materials Institute, Princeton University, Princeton NJ 08544. 2 Department of Physics, Pennsylvania State University, University Park PA 16802. 3 Institute for Inorganic and Analytical Chemistry, University of Mainz, Mainz, Germany. 4 Center for Neutron Research, NIST, Gaithersburg MD 20899.

Presenting Author: R.J. Cava

Cobalt based oxides display a wide range of magnetic and electronic properties. Their detailed study provides the opportunity for direct comparison to the cuprates to gain insight into what the unique characteristics of the cuprates really are. Here we report the synthesis and structural and physical characterization of metallic Co analogs of the Bi 2212 superconductor, and the insulating Co analogs of superconducting copper oxychlorides and La₂CaCu₂O₆. Their electronic and magnetic properties have been studied on small single crystals and polycrystalline samples. No superconductivity is observed. Electronic structure calculations have been performed to provide a first step for the analysis of the observed behavior.