Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session X3: Interface Phenomena in Oxides |
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Sponsoring Units: DCMP Chair: James Eckstein, University of Illinois Urbana Champaign Room: Morial Convention Center RO2 - RO3 |
Friday, March 14, 2008 8:00AM - 8:36AM |
X3.00001: 2D Superconductivity at the LaAlO$_{3}$/SrTiO$_{3}$ interface Invited Speaker: In 2004 Ohtomo and Hwang [1] discovered that the interface between two insulating oxides, LaAlO$_{3}$ and SrTiO$_{3}$ (both band insulators), is metallic with a high mobility. This publication triggered a lot of work around the world (see for instance [2, 3]). We have studied the ground state of this system and discovered superconductivity [4]. The studied LaAlO$_{3}$ samples are grown epitaxialy by pulsed laser deposition on TiO$_{2}$-terminated SrTiO$_{3}$ substrates and are annealed in situ in oxygen. The superconducting properties in the LaAlO$_{3}$/SrTiO$_{3}$ heterostructures display signatures of 2D superconductivity and agree with the Beresinskii-Kosterlitz-Thouless (BKT) predictions. However, for low currents, IV curves show some deviation from the expected behavior of a perfect infinite 2D system. These deviations are attributed to the finite lateral size of the measured path. Experiments to probe this size effect have been done to check this interpretation. \newline \newline [1] A. Ohtomo, H. Y. Hwang, Nature \textbf{427}, 423 (2004) \newline [2] S. Thiel, G. Hammerl, A. Schmehl, C. W. Schneider, J. Mannhart, Science \textbf{313}, 1942 (2006) \newline [3] A. Brinkman \textit{et al}, Nature Materials \textbf{6}, 493 (2007) \newline [4] N. Reyren \textit{et al}, Science \textbf{317}, 1196 (2007) [Preview Abstract] |
Friday, March 14, 2008 8:36AM - 9:12AM |
X3.00002: Magnetic effects at the interface between nonmagnetic oxides Invited Speaker: The electronic reconstruction at the interface between two insulating oxides can give rise to a highly conductive interface. In analogy to this remarkable interface-induced conductivity we show how, additionally, magnetic effects can be induced at the interface between the otherwise nonmagnetic insulating perovskites SrTiO$_{3}$ and LaAlO$_{3}$ [1]. A large negative magnetoresistance, up to 50\% at 50 mK, of the interface is found together with a logarithmic temperature dependence of the sheet resistance. These magnetic effects only appear in samples that have been grown under conditions that minimize the incorporation of oxygen vacancies. It is suggested that the interface electronic reconstruction induces localized magnetic moments in the SrTiO$_{3}$ that interact with the conduction electrons. At low temperatures, the sheet resistance reveals magnetic hysteresis with a long relaxation time scale. The conducting oxide interface now provides a versatile system to induce and manipulate magnetic moments in otherwise nonmagnetic materials. \\ \\{} [1] A. Brinkman \textit{et al}., Nature Materials \textbf {6}, 493 (2007). [Preview Abstract] |
Friday, March 14, 2008 9:12AM - 9:48AM |
X3.00003: Transport properties observed at hetero-interfaces of LaAlO$_{3}$ on SrTiO$_{3}$; intrinsic or extrinsic interface effect? Invited Speaker: We have made very thin films of LaAlO$_{3}$ on TiO$_{2}$ terminated SrTiO$_{3}$ and have measured the properties of the resulting interface in various ways. Transport measurements show a sheet carrier density of 10$^{16}$ cm$^{-2}$ and a mobility around 10$^{4}$ cm$^{2}$ V$^{-1}$ s$^{-1}$. \textit{In situ} UPS results indicate that oxygen vacancies play an important role in the creation of the charge carriers and that these vacancies are introduced by the pulsed laser deposition process used to make the hetero-interfaces [1]. Our results explain for the first time the origin of the large sheet carrier densities and high mobility observed previously [2]. XAS and spectroscopic ellipsometry [3] measurements confirm the existence of (oxygen) defects in the SrTiO$_{3}$. Simple model calculations confirm the plausibility of having defects at the origin of charge carriers while still maintaining a high mobility. By means of annealing experiments in atomic oxygen we try to answer the question whether an intrinsically doped interface does indeed exist at lower carrier concentrations [2]. Due to its reactive nature (i.e., binding energy in an oxygen molecule is about 5 eV), atomic oxygen will have much more power to eliminate any oxygen vacancies compared to conventional annealing methods. \newline [1] W. Siemons et al, Phys. Rev. B 76, 155111 (2007) \newline [2] W. Siemons et al., Phys. Rev. Lett. \textbf{98}, 196802 (2007) \newline [3] G. Lucovsky, H. Seo and J. Luning, unpublished [Preview Abstract] |
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