Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session L49: Focus Session: Spectrocopy, Magnetism, and Transport at LaAlO3/SrTiO3 Interfaces |
Hide Abstracts |
Sponsoring Units: DMP Chair: Jochen Mannhart, Max Planck Institute for Solid State Research Room: Mile High Ballroom 1C |
Wednesday, March 5, 2014 8:00AM - 8:36AM |
L49.00001: Photoemission spectroscopy studies of buried complex oxide interfaces Invited Speaker: Claudia Cancellieri At the interface between complex oxides, unexpected electronic properties different from those of the constituent bulk materials can arise. A particularly interesting example is the appearance of 2-dimensional conductivity at the interface of the band insulators LaAlO$_3$ (LAO) and SrTiO$_3$ (STO) above a critical LAO thickness of 4 unit cells. Photoemission spectroscopy is a powerful technique which directly probes the electronic structure of materials and can thus provide important information for a better understanding of their properties. The interface of LAO/STO has been investigated by soft x-ray photoelectron spectroscopy for different layer thicknesses across the insulator-to-metal interface transition. We measured clear spectroscopic signatures of Ti$^{3+}$ signal at the Fermi level in fully oxygenated sample. Our results show that Ti$^{3+}$-related charge carriers are present only for conducting samples, and are confined to a few monolayers from the interface. No Fermi-edge signal could be detected for insulating samples below the critical thickness. Polarization-controlled synchrotron radiation was subsequently used to map the electronic structure of conducting interfaces in a resonant angle-resolved photoemission experiment. A strong dependence on the light polarization of the Fermi surface and band dispersions is demonstrated, highlighting the distinct Ti~3$d$ orbitals involved in 2D conduction. Samples with different doping levels were prepared and measured by photoemission, revealing different band occupancies and Fermi-surface shapes. A direct comparison between the photoemission measurements and advanced first-principle calculations carried out for different 3$d$-band fillings is presented in conjunction with the 2D carrier concentration obtained from transport measurements. [Preview Abstract] |
Wednesday, March 5, 2014 8:36AM - 8:48AM |
L49.00002: Direct k-space mapping of the electronic structure in oxide-oxide interfaces M. Sing, F. Pfaff, J. Gabel, L. Dudy, G. Berner, P. Schuetz, H. Fujiwara, A. Yamasaki, Y. Saitoh, A. Sekiyama, S. Suga, V. Rogalev, V. Strocov, Y.Z. Chen, N. Pryds, R. Claessen Novel quantum phases can form at oxide heterointerfaces. Famous is the 2D electron system (2DES) in LaAlO$_3$/SrTiO$_3$ (LAO/STO). Its origin has been related to electronic reconstruction (ER). There electrons are transferred to the interface to compensate the potential gradient due to the polar discontinuity. The novel Al$_2$O$_3$ (AO)/STO also exhibits a 2DES but with much higher mobility [1]. In contrast to LAO, AO is regarded to be non-polar [1]. Hence ER should not be at work. It is assumed that O vacancies (Ovac) at the STO side of the interface induce the 2DES. We have directly mapped the k-resolved electronic structure of the interface states by resonant soft x-ray photoemission [2]. While we find a dichotomy of mobile and trapped charge -- the latter being ascribed to Ovac --, in both systems, they also show remarkable differences regarding the proportion of mobile and trapped carriers, the electron dispersions and Fermi surfaces, shedding light on the different role of Ovac.\\[4pt] [1] Y.Z. Chen et al, Nat. Comm. 4, 1371 (2013)\\[0pt] [2] G. Berner et al, PRL 110, 247601 (2013) [Preview Abstract] |
Wednesday, March 5, 2014 8:48AM - 9:00AM |
L49.00003: Orbital Inversion and Carrier Confinement in SrTiO$_{3}$/LaAlO$_{3}$ Interfaces Grown on NdGaO$_{3}$ Substrates Mark Golden, E. Slooten, B. Shi, B. Zwartsenberg, Z. Huang, T. Venkatesan, A. Annandi, M. Gorgoi, F. Radu, R. Abrudan, P. Miedema, C. Schuessler, J. Goedkoop, D. Doennig, J. Munding, R. Pentcheva, A. Ariando We investigate the role of the SrTiO$_{3}$ thickness on the electronic properties of heterointerfaces comprised of NdGaO$_{3}$ (bulk) / SrTiO$_{3}$ (n uc) / LaAlO$_{3}$ (15 uc) using X-ray linear dichroism (XLD) in absorption, Hard X-ray Photoemission Spectroscopy (HAXPES) and DFT$+$U calculations. XLD shows an orbital inversion for \textit{all} STO thicknesses: the lowest energy $d$-orbitals are of \textit{xz/yz} character, unlike `regular' STO/LAO, in which the \textit{xy} orbitals are lowest in energy. For n\textless 6 transport shows the carriers to be localized, HAXPES data showing electronic confinement to the NGO/STO interface. For STO thickness $\ge $8 uc, only weak localization is seen in transport, the STO/LAO interface becomes populated and carrier concentrations approaching half an electron per unit cell are deduced from both Hall measurements and HAXPES. Data from layer-resolved DFT$+$U calculations on STO/LAO and STO/NGO superlattices, and from NGO/STO/LAO are presented and compared to the experimental data, thereby providing a complete picture of the orbital polarization in these systems. [Preview Abstract] |
Wednesday, March 5, 2014 9:00AM - 9:12AM |
L49.00004: Electronic Orbital Reconstruction at (110)-oriented LaAlO$_{3}$/SrTiO$_{3}$ interfaces Gervasi Herranz, David Pesquera, Mateusz Scigaj, Nico Dix, Florencio Sanchez, Josep Fontcuberta, Pierluigi Gargiani, Javier Herrero, Eric Pellegrin, Manuel Valvidares, Alessandro Barla, Ruben Weht About ten years ago, a two-dimensional gas (2DEG) was discovered at the interface between two insulators: SrTiO$_{3}$ (STO) and LaAlO$_{3}$ (LAO). Later on, superconductivity as well magnetism were reported, making the LAO/STO interface an extremely intriguing system. So far the research was essentially directed to the (001)-interface, along which a built-in electrostatic potential is thought to generate the 2DEGs. Recently, however, high-mobility 2DEGs have been discovered along other directions, including \textless 110\textgreater for which such a built-in potential was unexpected. Yet, a direct fingerprint of the distinctive nature of the electronic structure at the (110)- interface has not been provided. Here, based on X-ray linear dichroism (XLD) experiments we show explicitly the dissimilar hierarchy of the electronic states at the (001)- and (110)- interfaces. In particular, our XLD experiments demonstrate that the degeneracy is fully removed in the t$_{\mathrm{2g}}$ and the e$_{\mathrm{g}}$ levels. Contrary to (001)- interfaces --where the first accessible orbitals are dxy--, our DFT calculations show, in agreement with XLD, a very strong contribution of the dxz/dyz orbitals at the first available levels in energy at (110)-interfaces. [Preview Abstract] |
Wednesday, March 5, 2014 9:12AM - 9:24AM |
L49.00005: An X-ray magnetic circular dichroism study of the interface Magnetism in titanate Heterostructures Marco Salluzzo The 2D-electron system (2DES) created at the interface between LaAlO$_{3}$ and SrTiO$_{3}$ have attracted strong interest in recent years. This system shows an intriguing inversion the Ti3d bands hierarchy at the interface respect the bulk [1], and some reports even suggested coexistence between ferromagnetism and superconductivity [2]. By using x-ray magnetic circular dichroism we show that oxygen vacancies induce magnetic interfacial localized Ti3$+$ states, which couple to the 2DES, with a negative exchange interaction. The magnetic dichroism signal is quenched in standard LAO/STO interfaces annealed in high oxygen pressure after the deposition and showing a homogeneous superconducting ground state [3], suggesting a decisive role of oxygen vacancies in the magnetism of these oxide interfaces [4,5]. \\[4pt] [1] M. Salluzzo, et al. Phys. Rev. Lett. 102, 166804 (2009); M. Salluzzo, et al., Adv. Mater. 25, 2333 (2013).\\[0pt] [2] J.A. Bert, et al., Nature Physics \textbf{7}, 767 (2011).\\[0pt] [3] D. Stornaiuolo, et al., Appl. Phys. Lett. 101, 222601 (2012).\\[0pt] [4] N. Pavlenko, et al., Phys. Rev. B 85, 020407(R) (2012).\\[0pt] [5] M. Salluzzo, et al., Phys. Rev. Lett. 111, 087204 (2013). [Preview Abstract] |
Wednesday, March 5, 2014 9:24AM - 9:36AM |
L49.00006: Competition between Kondo screening and Magnetism in the LaAlO3/SrTiO3 Interface Jonathan Ruhman, Arjun Joshua, Shahal Ilani, Ehud Altman We present a theory of magnetic phenomena at LaAlO3/SrTiO3 interfaces, which includes coupling between the conduction bands and local magnetic moments originating from charge traps at the interface. Tuning the itinerant electron density drives transitions between a heavy Fermi liquid phase with screened moments and various magnetic states. The dependence of the magnetic phenomena on the electron density stems from competing magnetic interactions between the local moments and the different conduction bands. At low densities only the lowest conduction band, composed of the $d_{xy}$ orbitals of Ti, is occupied. Its antiferromagnetic interaction with the local moments leads to screening of the moments at a Kondo scale that increases with density. However, above a critical density the $d_{xz}/d_{yz}$ bands begin to populate. Their ferromagnetic interaction with the local moments competes with the antiferromagnetic interaction of the $d_{xy}$ band leading to eventual reduction of the Kondo scale with density. We explain the distinct magneto transport regimes seen in experiments as manifestations of the magnetic phase diagram computed from the model. We also present interpretation of previously unpublished data supporting the theoretical model. [Preview Abstract] |
Wednesday, March 5, 2014 9:36AM - 9:48AM |
L49.00007: Magnetism at Amorphous Oxide Interfaces Spencer Tomarken, Andrea Young, Sang Woon Lee, Roy Gordon, Raymond Ashoori Recent work has shown that a mobile interfacial electron gas is created when certain amorphous transition metal oxides are grown on strontium titanate. We report torque magnetometry and transport measurements on a series of STO-based oxide heterostructures with amorphous overlayers grown by atomic layer deposition. We observe in-plane ferromagnetic ordering that is qualitatively similar to results observed in crystalline LAO/STO samples. We will discuss the implications of these results on the origin of magnetism in both polar and amorphous oxide interfaces. [Preview Abstract] |
Wednesday, March 5, 2014 9:48AM - 10:00AM |
L49.00008: Room-Temperature Electronically-Controlled Ferromagnetism at the LaAlO$_3$/SrTiO$_3$ Interface Feng Bi, Mengchen Huang, Chung-Wung Bark, Sangwoo Ryu, Chang-Beom Eom, Patrick Irvin, Jeremy Levy Reports of emergent conductivity, superconductivity, and magnetism at oxide interfaces have helped to fuel intense interest in their rich physics and technological potential. We employ magnetic force microscopy to search for room-temperature magnetism in the well-studied LaAlO$_3$/SrTiO$_3$ system.\footnote{F. Bi, \textit{et al.}, arXiv:1307.5557} Using electrical top gating to deplete electrons from the oxide interface, we directly observe an in-plane ferromagnetic phase with sharply defined domain walls. Itinerant electrons, introduced by a top gate, align antiferromagnetically with the magnetization, at first screening and then destabilizing it as the conductive state is reached. Subsequent depletion of electrons results in a new, uncorrelated magnetic pattern. This newfound control over emergent magnetism at the interface between two non-magnetic oxides portends a number of important technological applications. [Preview Abstract] |
Wednesday, March 5, 2014 10:00AM - 10:12AM |
L49.00009: A suggestion for making the ferromagnetism at perovskite oxide interfaces robust Nirmal Ganguli, Paul Kelly LaAlO$_3|$SrTiO$_3$ heterostructures have received much attention following observations of ferromagnetism, superconductivity and of an insulator to metal transition at the interface between otherwise conventional band insulators. One of the challenges posed by recent observations is to understand how high mobility charge carriers and local magnetic moments can coexist at $n$-type interfaces where the lack of a detailed knowledge of the interface structure from experiment is a major impediment to understanding these physical properties. A more extensive first principles study of the ferromagnetically ordered state found for modest values of Hubbard $U$ in the presence of GdFeO$_3$-type octahedral tilts at the interface [1] suggests that it should be possible to make the interface ferromagnetism more robust by enhancing the octahedral tilts. We screened a number of oxide interfaces with first principles calculations and identified the LaAlO$_3|$CaTiO$_3$ (001) interface as the most promising candidate in the large charge transfer limit, owing to the large intrinsic tilt of TiO$_6$ octahedra in CaTiO$_3$.\\[4pt] [1] Z. Zhong and P. J. Kelly, Europhys. Lett. \textbf{84}, 27001 (2008) [Preview Abstract] |
Wednesday, March 5, 2014 10:12AM - 10:24AM |
L49.00010: Band alignments at oxide interfaces and consequences for devices Chris Van de Walle, Lars Bjaalie, Burak Himmetoglu, Leigh Weston, Anderson Janotti Oxide heterostructures have been shown to exhibit unusual physics and hold the promise of novel electronic applications. We present a set of criteria to select and design interfaces, particularly those that can sustain a high-density two-dimensional electron gas (2DEG). We describe how first-principles calculations, based on hybrid density functional theory, can contribute to a qualitative and quantitative understanding, illustrated with the key issue of band alignment. Band offsets determine on which side of the interface the 2DEG will reside, as well as the degree of confinement. We present band alignments for a number of complex oxides, considering materials with different types of conduction-band character, polar or nonpolar character, and band insulators as well as Mott insulators. We suggest promising materials combinations that could lead to a 2DEG with optimized properties, such as high 2DEG densities and high electron mobilities. [Preview Abstract] |
Wednesday, March 5, 2014 10:24AM - 10:36AM |
L49.00011: Low Temperature Transport of LaAlO$_3$/SrTiO$_3$ interfaces Stefano Gariglio, Alexandre Fete, Danfeng Li, Daniela Stornaiuolo, Jean-Marc Triscone The conducting interface between the two band insulators LaAlO$_3$ and SrTiO$_3$ has drawn a large share of attention, as it presents a variety of exciting electronic properties that are tunable by an electric field [1]. At low temperatures, magnetotransport analysis has revealed a strong Rashba spin-orbit interaction originating from the breaking of inversion symmetry [2] and, in field effect devices, the ground state has been tuned from an insulating to a superconducting state. I will discuss these results in light of recent magnetotransport experiments in field-effect devices to probe the evolution across the phase diagram of the weak localization /weak anti-localization transport regime, its relation to the strength and anisotropy of the superconducting state. \\[4pt] [1] A. D. Caviglia \textit{et al.}, Nature \textbf{456}, 624 (2008).\\[0pt] [2] A. D. Caviglia \textit{et al.}, Phys. Rev. Lett. \textbf{104}, 126803 (2010); A. F\^ete \textit{et al.}, Phys. Rev. B \textbf{86}, 201105 (2012). [Preview Abstract] |
Wednesday, March 5, 2014 10:36AM - 10:48AM |
L49.00012: Superconducting Interfaces between Artificially-Grown LaAlO$_3$ and SrTiO$_3$ Thin Films Danfeng Li, Stefano Gariglio, Claudia Cancellieri, Alexandre Fete, Daniela Stornaiuolo, Jean-Marc Triscone Realization of a fully metallic two-dimensional electron gas (2DEG) at the interface between artificially-grown LaAlO$_3$ and SrTiO$_3$ thin films has been an exciting challenge. Here we present for the first time the successful realization of a superconducting 2DEG at interfaces between artificially-grown LaAlO$_3$ and SrTiO$_3$ thin films. Our results highlight the importance of two factors - the growth temperature and the SrTiO$_3$ termination. We use local friction force microscopy and transport measurements to determine that in normal growth conditions the absence of a robust metallic state at low temperature in the artificially-grown LaAlO$_3$/SrTiO$_3$ interface is due to the nanoscale SrO segregation occurring on the SrTiO$_3$ film surface during the growth and the associated defects in the SrTiO$_3$ film. By adopting an extremely high SrTiO$_3$ growth temperature, we demonstrate a way to realize metallic, down to the lowest temperature, and superconducting 2DEG at interfaces between LaAlO$_3$ layers and artificially-grown SrTiO$_3$ thin films. This study paves the way to the realization of functional LaAlO$_3$/SrTiO$_3$ superlattices and/or artificial LaAlO$_3$/SrTiO$_3$ interfaces on other substrates. [Preview Abstract] |
Wednesday, March 5, 2014 10:48AM - 11:00AM |
L49.00013: Quantum oscillations and Hall plateaus at LaAlO$_{3}$/SrTiO$_{3}$ interface Yanwu Xie, Christopher Bell, Yasuyuki Hikita, Harold Y. Hwang In this work, we tuned the sheet carrier density and mobility of the quasi-two-dimensional electron gas (q2DEG) confined at the LaAlO$_{3}$/SrTiO$_{3}$ interface by surface control, and studied the magneto-transport behavior of the q2DEG. We observed a universal trend that mobility increases with decreasing sheet carrier density, with a maximum mobility of \textgreater 20,000 cm$^{2}$V$^{-1}$s$^{-1}$. In a low sheet carrier density regime, we observed well resolved Shubnikov-de Haas quantum oscillations in the longitudinal resistance, and a plateau-like structure in the Hall conductivity. The frequency of the quantum oscillations shows a clear transition with increasing magnetic field, with a high / low field frequency ratio close to 3. In addition, the Landau indices of the plateaus in the Hall conductivity data show spacing close to 4, in units of the quantum of conductance. These features can be understood by considering magnetic breakdown orbits and account for all of the carriers. [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