Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session V5: Surfaces and Interfaces of Correlated Oxides |
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Sponsoring Units: DMP Chair: James Eckstein, University of Illinois Room: Baltimore Convention Center 309 |
Thursday, March 16, 2006 11:15AM - 11:51AM |
V5.00001: Magnetic Oxide Superlattices Invited Speaker: Atomically regulated interfaces and superlattices composed of oxides are very interesting research arena for physics and possible applications. By selecting magnetic oxides as one of the components, one can study basic phenomena of spin polarized electrons at the interfaces [1]. Also, one can realized ?multiferroics? at the interface because magnetization and electric dipole due to interface charge imbalance can coexist. We demonstrated that non-linear Kerr effect [2] can be a tool of detecting interface magnetism in ?tricolor superlattices? composed of asymmetric A-B-C-A-B-C- sequence with A, B, and C being component oxides [3]. This technique was successfully applied to detect, design and enhance interface magnetism in a single heterointerface [4]. We now extend the artificially built-in multiferroic superlattices to other sequences, which include DNA superlattices (D: donor, N: neutral, and A: acceptor) and Ratchet superlattices (asymmetric doping profile). We also demonstrate realization of interface ferromagnetism at pn junctions made of two Mott insulators and tuning the magnitude through the channels of orbital and charge degrees of freedom. \newline \newline [1] M. Izumi et. al., J. Phys. Soc. Jpn., 71, 2621 (2002), Phys. Rev. B 64, 064429 (2001). \newline [2] Y. Ogawa, et. al., Phys. Rev. Lett., 90. 217403 (2003). \newline [3] H. Yamada, at. al., Appl. Phys. Lett., 80, 622 (2002). \newline [4] H. Yamada, et. al., Science, 305, 646 (2004). [Preview Abstract] |
Thursday, March 16, 2006 11:51AM - 12:27PM |
V5.00002: Electrostatic Modulation of the Charge Density of Correlated Oxides Invited Speaker: A commonly occurring feature of correlated complex oxides is the sensitivity of their physical properties to changes in the carrier concentration. Modification of the carrier concentration is typically accomplished through chemical doping, which can introduce chemical and structural disorder into the system. Here, we discuss electric field effect experiments on colossal magnetoresistive manganites, showing the possibility of inducing large, reversible changes in the magnetic properties through electrostatic modulation of the carrier concentration. We compare electrostatic doping with chemical doping, showing that differences in transport properties arise because of structural distortions that occur during chemical substitution. [Preview Abstract] |
Thursday, March 16, 2006 12:27PM - 1:03PM |
V5.00003: Ferromagnet / superconductor oxide superlattices Invited Speaker: The growth of heterostructures combining oxide materials is a new strategy to design novel artificial multifunctional materials with interesting behaviors ruled by the interface. With the (re)discovery of colossal magnetoresistance (CMR) materials, there has been renewed interest in heterostructures involving oxide superconductors and CMR ferromagnets where ferromagnetism (F) and superconductivity (S) compete within nanometric distances from the interface. In F/S/F structures involving oxides, interfaces are especially complex and various factors like interface disorder and roughness, epitaxial strain, polarity mismatch etc., are responsible for depressed magnetic and superconducting properties at the interface over nanometer length scales. In this talk I will focus in F/S/F structures made of YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO) and La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ (LCMO). The high degree of spin polarization of the LCMO conduction band, together with the d-wave superconductivity of the YBCO make this F/S system an adequate candidate for the search of novel spin dependent effects in transport. We show that superconductivity at the interface is depressed by various factors like charge transfer, spin injection or ferromagnetic superconducting proximity effect. I will present experiments to examine the characteristic distances of the various mechanisms of superconductivity depression. In particular, I will discuss that the critical temperature of the superconductor depends on the relative orientation of the magnetization of the F layers, giving rise to a new giant magnetoresistance effect which might be of interest for spintronic applications. Work done in collaboration with V. Pe\~{n}a$^{1}$, Z. Sefrioui$^{1}$, J. Garcia-Barriocanal$^{1}$, C. Visani$^{1}$, D. Arias$^{1}$, C. Leon$^{1}$ , N. Nemes$^{2}$, M. Garcia Hernandez$^{2}$, S. G. E. te Velthuis$^{3}$, A. Hoffmann$^{3}$, M. Varela$^{4}$, S. J. Pennycook$^{4}$. Work supported by MCYT MAT 2005-06024, CAM GR- MAT-0771/2004, UCM PR3/04-12399 Work at Argonne supported by the Department of Energy, Basic Energy Sciences, contract No.W-31-109-ENG-38. \newline \newline $^{1}$\textit{GFMC, Departamento de F\'{\i}sica Aplicada III, Universidad Complutense de Madrid, 28040 Madrid, Spain} \newline $^{2}$\textit{Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC). 28049 Cantoblanco. Madrid}. \newline $^{3}$\textit{Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA} \newline $^{4}$\textit{Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6031, USA} [Preview Abstract] |
Thursday, March 16, 2006 1:03PM - 1:39PM |
V5.00004: (Giant) Proximity Effects in high-T$_{c}$ superlattices Invited Speaker: Molecular beam epitaxy enables one to synthesize HTS thin films with rms surface roughness in the range 0.2-0.5 nm, much less than the unit cell height (1-2 nm).$^{1}$ One can also make atomically smooth multilayers and superlattices in which HTS or spacer layers can be just one unit cell thick if so desired. A detailed study of transport properties of such heterostructures has already revealed some unexpected findings.$^{2 }$In junctions where the barrier is made out of underdoped cuprate with a reduced critical temperature $T_{c}$, we observe the Giant Proximity Effect: supercurrent runs through very thick barrier layers even at temperature well above $T_{c}$ (contrary to what is expected from the standard theory).$^{ }$Atomic smoothness of films and multilayers, excellent device uniformity, and reversible modulation of barrier properties by oxygen intake provided solid evidence against experimental artifacts such as pinholes and micro-shorts. Hence, the effect is real and intrinsic, and it defies the conventional explanation. Interpretation and significance of our experimental results will be discussed in the context of theoretical concepts such as the pseudogap, midgap states, electronic inhomogeneity, preformed pairs, and possibly resonant pair tunneling. The work at BNL is done in collaboration with G. Logvenov, V. Butko, A. Gozar and A. Bollinger. \newline $^{1 }$\textit{I. Bozovic et al., Phys. Rev. Lett. }\textbf{\textit{89}}\textit{, 107001 (2002); }\textit{P. Abbamonte et al., Science}\textbf{\textit{ 297}}\textit{, 581 (2002).} \newline $^{2 }$\textit{I. Bozovic et al., Nature }\textbf{\textit{421}}\textit{, 873 (2003); Phys. Rev. Lett. }\textbf{\textit{93}}\textit{, 157002 (2004).} [Preview Abstract] |
Thursday, March 16, 2006 1:39PM - 2:15PM |
V5.00005: Surprising Properties of Interfaces in the Cuprate Superconductors Invited Speaker: Interfaces in the cuprate superconductors, in particular the grain boundaries, play a decisive role for the realization of large scale applications of these materials, such as superconducting power cables. The approach followed worldwide to optimize the boundaries for superconducting cables consists in aligning all grains in the cables to less than 10\r{ }, which presents an enormous effort. From the viewpoint of a solid state physicist, the grain boundaries in the cuprates are interfaces at which two oxides with highly correlated electron systems meet. If described as linear defects in the CuO$_{2}$-planes, can the properties of the boundaries be understood and new approaches for their optimization be identified? To address these questions, we have performed experiments to study the properties of these interfaces below and above the superconducting transition temperature. We find for the superconducting as well as for the normal state startling phenomena which challenge our understanding of the underlying physics. [Preview Abstract] |
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