Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session P34: Focus Session: Interfaces in Complex Oxides - Transport and Optics |
Hide Abstracts |
Sponsoring Units: DMP Chair: Jean-Marc Triscone, University of Geneva Room: C141 |
Wednesday, March 23, 2011 8:00AM - 8:12AM |
P34.00001: Electrodynamics and electronic structure of LVO/SVO superlattices investigated by optical spectroscopy Da Woon Jeong, Woo Seok Choi, Tae Dong Kang, David Adrian, Yun Sang Lee, Wilfrid Prellier, Tae Won Noh Perovskite vanadium oxide has intriguing coupling between orbital, spin and lattice degrees of freedom that bears novel physical properties. For example, filling controlled insulator to metal transition could be observed in (La$_{1-x}$Sr$_{x})$VO$_{3}$, and orbital ordering was predicted theoretically for the interface valence state (V$^{3.5+})$ between LaVO$_{3}$ and SrVO$_{3}$ [1]. Here, we investigated the charge dynamics and electronic structures of (LaVO$_{3})_{6m}$(SrVO$_{3})_{m}$ (m=1,2, and 4) superlattices using optical spectroscopy. We found a reduction of Drude spectral weight as the superlattice periodicity is decreased, consistent with the transport result [2]. Moreover, interband transition of (LaVO$_{3})_{6}$(SrVO$_{3})_{1}$ was quite different from other larger period superlattices. New peak structure at 3.5eV was developed possibly due to the correlation between the electronic structure and orbital confinement. Electrodynamics and electronic structure reconstruction will be discussed.\\[4pt] [1] G. Jackeli \textit{et al}., PRL, \textbf{101}, 216804 (2008)\\[0pt] [2] W. C. Sheets \textit{et al}., APL \textbf{91}, 192102 (2007) [Preview Abstract] |
Wednesday, March 23, 2011 8:12AM - 8:24AM |
P34.00002: Geometrically confined doping in LaVO$_{3}$/SrVO$_{3}$ superlattices U. Lueders, A. David, Ph. Boullay, R. Fr\'esard, W. Prellier, P.-E. Janolin A number of theoretical predictions show that in complex oxides the confinement of t$_{2g}$ electrons to two dimensions can alter strongly the physical properties of these systems compared to their 3D counterpart. To approach experimentally the 2D limit we propose geometrically confined doped superlattices as LaVO$_{3}$/SrVO$_{3}$. Here, a one unit cell thick layer of SrVO$_{3}$ is introduced between insulating LaVO$_{3}$ layers to create conducting zones with a 2D character. We synthesized this kind of superlattices by PLD on SrTiO$_{3}$ (001) substrates. The 2D character of the doped charge carriers influences strongly the physical properties of the superlattices. While the bulk solid solution is an insulating antiferromagnet, in the superlattices, room-temperature magnetism is observed due to the reduction of the bandwidth and a transition from a high temperature weakly localized phase to a low temperature metallic phase is shown to be connected to a structural transition from a metrically tetragonal to monoclinic phase. With the help of theoretical calculations, we will show that these peculiar properties are due to a change of the orbital physics in the vicinity of the SrVO$_{3}$ doping layers. [Preview Abstract] |
Wednesday, March 23, 2011 8:24AM - 8:36AM |
P34.00003: Theory of LaVO$_3$/SrVO$_3$ superlattices Hung Dang, Andrew Millis We present dynamical mean field theory calculation and compare to experimental data [1] of the magnetic, orbital order and metal-insulator phase diagrams of LaVO$_3$/SrVO$_3$ superlattices. The calculation is based on a three-orbital model system; semiclassical and quantum Monte Carlo impurity solvers are used. \\[4pt] [1] U. Luders, W. C. Sheets, A. David, W. Prellier, and R. Fresard, Phys. Rev. B 80, 241102(R) (2009). [Preview Abstract] |
Wednesday, March 23, 2011 8:36AM - 9:12AM |
P34.00004: New Optical Absorption Bands in Atomic Layer Superlattices Invited Speaker: Using atomic layer-by-layer molecular beam epitaxy, atomic layer superlattices can be constructed that exhibit new electronic, optical and lattice effects not present in the individual components. In particular, new optical transitions giving rise to sharp absorption peaks can be created by placing a layer of a material with occupied source states next to a layer of another material with unoccupied destination states. We combine atomic layers of SrTiO$_{3}$ and LaMnO$_{3}$ into superlattice structures with component layers as thin as single monolayer and find a new absorption band due to a transition from manganese- to titanium-derived states. The energy of the new transition depends on how the bands line up at the interface. Furthermore, a substantial shift of spectral weight occurs as well, while retaining a constant sum rule. This work was supported by the Department of Energy Basic Energy Sciences at the Fredrick Seitz Materials Research Laboratory, University of Illinois, Urbana. This work was done in collaboration with Xiaofang Zhai, Mao Zheng, Amish Shah, Chandra Mohapatra, and Jian-Min Zuo. [Preview Abstract] |
Wednesday, March 23, 2011 9:12AM - 9:24AM |
P34.00005: Colossal Magnetoresistance in thin films of the Mott metal CaVO$_{3 }$ Jiwei Lu Bulk CaVO$_{3}$ (CVO) is a Pauli paramagnetic metal with a singe 3d electron. Some unusual drastic changes in the magneto-resistance, magnetic susceptibility and the Hall effect have been reported in single crystal CVO. We have simultaneously synthesized epitaxial CVO films grown on three differently oriented SrTiO$_{3}$ substrates. The temperature dependent conductivity of these CVO films demonstrated very strong Fermi metal behavior and the resistance ratio, defined as R(300 K)/R (2K) was more than 3000. Colossal magneto-resistance (MR) as well as large crystalline anisotropic was observed at low temperatures. The maximum MR, defined as (R(7 T)-R(0 T))/R(0 T)*100 {\%}, was over 1500 {\%} at 2 K and 7 Telsa on the CVO films deposited on a (110) SrTiO3 single crystal substrate, and didn't show any sign of saturation. An MR of over $\sim $ 500 {\%} and $\sim $ 200 {\%} were observed on (111) and (100) orientation films under the same condition, respectively. The MR ratio was much larger than that of single crystal CVO. We will discuss the peculiar MR in association with the magnetic ordering, oxygen stoichiometry and Fermi surface. [Preview Abstract] |
Wednesday, March 23, 2011 9:24AM - 9:36AM |
P34.00006: High frequency conductivity of few unit cell thick LaNiO$_{3}$ layers Daniel Ouellette, Junwoo Son, Susanne Stemmer, S. James Allen We have measured the dc and optical conductivity of ultra-thin films of the correlated metal LaNiO$_{3}$ and of superlattices with alternating LaNiO$_{3}$ and insulating SrTiO$_{3}$ layers, all grown epitaxially on LSAT substrates with modest tensile strain in the LaNiO$_{3}$. In the superlattices, the LaNiO$_{3}$ layers are 4 unit cells (1.6 nm) thick and the SrTiO$_{3}$ is either 4 or 10 unit cells thick. Isolated films thinner than 4 nm are insulating; however, both the superlattices and thicker films consistently show a coherent peak in the optical conductivity. Furthermore, the optical conductivity at several hundred GHz is in excellent agreement with the dc electrical conductivity. We consider the possibility of a percolation threshold in ultra-thin LaNiO3 layers and discuss implications for the nature of the LaNiO$_{3}$/SrTiO$_{3}$ interface. [Preview Abstract] |
Wednesday, March 23, 2011 9:36AM - 9:48AM |
P34.00007: Quasi 2D correlated metals: Unusual transport properties in strained heteroepitaxial ultrathin films E.J. Moon, B.A. Gray, J. Liu, M. Kareev, B. Dabrowski, J.W. Freeland, I-C. Tung, M.J. Bedzyk, L.H. Tjeng, S.G. Altendorf, F. Strigari, V.P. Kunets, G.J. Salamo, J. Chakhalian We explore the electrical transport and magnetoconductance in quasi 2D strongly correlated heteroepitaxial films of LaNiO$_3$ to investigate the effect of quantum confinement and strain on electron-electron and electron-lattice interactions over the whole temperature range (2-300K) including the effect of metal-insulator transition. The quantum corrections to the conductivity indicate that the combination of the weak localization and the electron-electron interaction in the quasi 2D limit gives rise to unusual T-dependent resistivity. Ultrathin films spanning tensile strain up to $\sim$4$\%$ are used to obtain the enhanced driving effects between the two corrections for the observed localization at low temperatures. Intrinsic transport properties of strained LaNiO$_3$ films with the characteristic multi-band structure will be discussed. [Preview Abstract] |
Wednesday, March 23, 2011 9:48AM - 10:00AM |
P34.00008: Strain-modified thermopower of ultrathin LaNiO$_3$ films Narayan Prasai, Joshua Cohn, Eun Ju Moon, Jian Liu, Michael Kareev, Benjamin Gray, Jak Chakhalian, James Rondinelli The influence of epitaxial strain on electronic transport in the correlated metal LaNiO$_3$ is investigated through measurements of thermopower (TEP) in the temperature range $5{\rm K}\leq {\rm T}\leq 330 {\rm K}$ on a series of fully-strained, 10-unit-cell-thick films grown by pulsed-laser deposition on (100)-oriented YAlO$_3$, LaAlO$_3$, SrTiO$_3$, and GaScO$_3$ substrates. The TEP exhibits an electron-like, linear-$T$ contribution for $T\geq 150$~K with a slope approximately independent of strain, but a magnitude that varies systematically with strain. A peak in the TEP at $T\approx 25$~K also correlates with strain and is unaffected by a 9-T magnetic field. The implications of these results for strain-modified charge-carrier diffusion and phonon drag contributions to the TEP will be discussed. [Preview Abstract] |
Wednesday, March 23, 2011 10:00AM - 10:12AM |
P34.00009: Strain control of the metal-insulator transition of NdNiO3 epitaxial ultrathin films Jian Liu, M. Kareev, B. Gray, P. Ryan, J.W. Kim, J.W. Freeland, J. Chakhalian Metal-insulator transition (MIT) is the hallmark of strongly correlated electron systems. It often couples with the multiple degrees of freedom of $d$ electrons in complex oxides, resulting in diverse and intriguing properties. While MIT has been studied for decades, heteroepitaxy is emerging as a promising way to manipulate correlated electrons and stabilize unusual phases in nanostructures. Understanding its effect on the MIT in ultrathin structures is fundamentally and technologically critical. To this end, we have grown perfectly strained atomic layers of NdNiO3 by laser MBE on a series of substrates with large variation in lattice mismatch. The extensive measurements including electric and thermal transport, synchrotron based XRD and XAS show dramatic modifications of electronic properties with lattice mismatch. Possible microscopic mechanisms are discussed. J.C. was supported by DOD-ARO under the Contract No. 0402-17291 and NSF Contract No. DMR-0747808. [Preview Abstract] |
Wednesday, March 23, 2011 10:12AM - 10:24AM |
P34.00010: Two-dimensional electron gas in SrTiO$_{3}$ Bharat Jalan, S. James Allen, Susanne Stemmer We report on Shubnikov-de Haas (SdH) oscillations in a two-dimensional electron gas (2DEG) in delta-doped SrTiO$_{3}$ thin films. The existence of a 2DEG is confirmed by the angular dependence of the SdH oscillations. The observed SdH oscillation frequency corresponds to a carrier concentration of, which is only 4{\%} of the total Hall carrier density. We show that the only electrons in one of the sub-bands confined by the delta-doping potential have sufficient mobility to exhibit quantum oscillations. Guided by the similarity of the confined $d$-band electron states in SrTiO$_{3}$ to the confined hole systems in conventional semiconductors, quantum oscillations are interpreted in terms of spin and Landau level splitting. Despite the inherent complexity of a sub-band that is derived from four $d$-band states near the conduction band minimum of SrTiO$_{3}$, we show that the quantum oscillations can be modeled quantitatively. Alternative routes to realize high mobility 2DEGs in SrTiO$_{3}$ will also be discussed. [Preview Abstract] |
Wednesday, March 23, 2011 10:24AM - 10:36AM |
P34.00011: High Temperature Conductance Characteristics of Differently Modified LaAlO$_{3}$/SrTiO$_{3}$-Heterostructures Felix Gunkel, Susanne Hoffmann-Eifert, Jos\'{e}e E. Kleibeuker, Peter Brinks, Mark Huijben, Guus Rijnders, Gertjan Koster, Regina Dittmann, Rainer Waser In order to understand the physical origin of the high charge carrier density at the conducting interface between SrTiO$_{3}$ (STO) and LaAlO$_{3}$ (LAO) the role of defects has to be clarified. In this study, LAO/STO-heterostructures modified in stacking sequence and growth conditions were investigated by means of high temperature conductance (HTC) measurements under changing oxygen ambience. Under measurement conditions the samples are in equilibrium with the surrounding oxygen atmosphere, which rules out the effect of mobile oxygen vacancies on the interface conductivity [Gunkel et al., APL 97(2010)]. The HTC characteristics show a significant dependency on the preparation procedure of STO and LAO close to the interface. Nevertheless, a common conduction and charge compensation mechanism can be identified. The results are discussed with respect to the defect chemistry model of perovskite oxides. [Preview Abstract] |
Wednesday, March 23, 2011 10:36AM - 10:48AM |
P34.00012: Magnetotransport behavior of LaAlO$_3$/SrTiO$_3$ and Ar-irradiated SrTiO$_3$: implications on Rashba Spin-Orbit coupling and magnetism in quasi-2-dimensional electron gases J.H. Ngai, Y. Segal, F.J. Walker, S. Ismail-Beigi, K. LeHur, C.H. Ahn, D. Su, Y. Zhu Quasi 2-dimensional electron gases (Q2DEG) in complex oxide heterostructures exhibit a wide range of tunable behavior that promises potentially new functionalities. In particular much interest has focused on the Q2DEG at the LaAlO$_3$/SrTiO$_3$ interface, where evidence for Rashba spin-orbit coupling and magnetic behavior has recently been found through magnetotransport measurements. At present it is unclear whether the spin-orbit and magnetic effects are unique to the LaAlO$_3 $/SrTiO$_3$ interface, or if they arise from the properties of doped SrTiO$_3$. In order to shed light on this issue, we compare the magnetotransport properties of LaAlO$_3$/SrTiO$_3$ and Ar$^+$-irradiated SrTiO$_3$. Strikingly similar magnetotransport behavior is observed between LaAlO$_3$/SrTiO$_3 $ and Ar$^+$-irradiated Q2DEGs. However, our analysis indicates changes in the confinement or thickness of the Q2DEG can account for the magnetotransport observed. Implications of our results on Rashba spin-orbit coupling and magnetism at the LaAlO$_3$/SrTiO$_3$ interface will be discussed. [Preview Abstract] |
Wednesday, March 23, 2011 10:48AM - 11:00AM |
P34.00013: Can an oxygen vacancy form a Kondo center at the LaAlO$_3$/SrTiO$_3$ interface? Mohammad Sherafati, Birabar Nanda, Sashi Satpathy Recently a Kondo resistance minimum has been observed at the interface between LaAlO$_3$ and SrTiO$_3$[1]. It has been suggested that the effect is due to the scattering of interface electrons from magnetic centers just like in the original Kondo effect; however, the origin of such magnetic centers is not understood. In this work, we evaluate the idea of whether an oxygen vacancy in SrTiO$_3$ might produce a magnetic center. We focus on an isolated vacancy in bulk SrTiO$_3$ from density-functional calculations and provide evidence that of the two electrons released to the system by the oxygen vacancy, one becomes localized near the vacancy site, while the other forms a delocalized state. The results suggest that the localized electron could form a Kondo center resulting in a resistance minimum as observed in the experiments. \\[4pt] [1] A. Brinkman {\it et al.}, Nature Mater. {\bf 6} 493 (2007). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700