Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session K37a: Complex Oxide Interfaces and Heterostructures - Oxide 2-DEGsFocus
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Sponsoring Units: DMP DCMP Chair: Bharat Jalan, University of Minnesota Room: 383 |
Wednesday, March 15, 2017 8:00AM - 8:36AM |
K37a.00001: TBD - Complex Oxide Interfaces and Heterostructures Invited Speaker: Masachi Kawasaki |
Wednesday, March 15, 2017 8:36AM - 8:48AM |
K37a.00002: Formation of 2DEG at the interface of unconventional oxide hetero-structures by atomic layer deposition. Farida Selim, Dave Winarski, Kevin Leedy, David Look Two-dimensional electron gases (2DEGs) with a sheet carrier density of 10$^{\mathrm{14}}$ cm$^{\mathrm{-2}}$ and high electron mobility have been realized at the interface of SrTiO$_{\mathrm{3}}$ and Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ films grown by atomic layer deposition at very low temperatures. Possible origins for the high electron densities will be discussed. By controlling the interface, the sheet resistance exhibited a wide range of change from 10$^{\mathrm{3}}$ to 10$^{\mathrm{13\thinspace }}\Omega $/square. Temperature dependent Hall-effect measurements revealed metallic conduction and metal-semiconductor transitions. The effect of growth parameters, surface conditions, and film thickness on the transport properties of the interface will be discussed. [Preview Abstract] |
Wednesday, March 15, 2017 8:48AM - 9:00AM |
K37a.00003: Tunable anomalous orbital structure in a spinel-perovskite interface $\gamma $-Al$_{2}$O$_{3}$/SrTiO$_{3}$ Yanwei Cao, Xiaoran Liu, Padraic Shafer, SriManta Middey, Derek Meyers, Mikhail Kareev, Zhicheng Zhong, Jong-Woo Kim, Philip Ryan, Elke Arenholz, Jak Chakhalian In all archetypical reported (001)-oriented perovskite heterostructures, for example LaTiO$_{3}$/SrTiO$_{3}$, LaAlO$_{3}$/SrTiO$_{3}$, YTiO$_{3}$/SrTiO$_{3}$ and so on, it has been deduced that the preferential occupation of two-dimensional electron gases is in-plane d$_{xy}$ state. In sharp contrast to this, the investigated electronic structure of a spinel-perovskite heterostructure $\gamma $-Al$_{2}$O$_{3}$/SrTiO$_{3}$ by resonant soft X-ray linear dichroism, demonstrates that the preferential occupation is in out-of-plane d$_{xz}$/d$_{yz}$ states for interfacial electrons. Moreover, the impact of strain further corroborates that this anomalous orbital structure can be linked to the altered crystal field at the interface and symmetry breaking of the interfacial structural units. Our findings provide another interesting route to engineer emergent quantum states with deterministic orbital symmetry. [Preview Abstract] |
Wednesday, March 15, 2017 9:00AM - 9:12AM |
K37a.00004: New type of in-gap states at a spinel/perovskite interface: combined resonant soft x-ray photoemission spectroscopy and first-principles study. Vladislav Borisov, Philipp Schuetz, Florian Pfaff, Philipp Scheiderer, Lenart Dudy, Michael Zapf, Judith Gabel, Dennis Valbjorn Christensen, Yunzhong Chen, Nini Pryds, Vladimir Strocov, Victor Rogalev, Christoph Schlueter, Tien-Lin Lee, Harald O. Jeschke, Roser Valenti, Michael Sing, Ralph Claessen Oxygen vacancies in oxide heterostructures create a plethora of electronic phenomena not observed in the stoichiometric systems. In this talk we will discuss the presence of a new type of in-gap states at the spinel/perovskite $\gamma$-Al$_2$O$_3$/SrTiO$_3$ interface [1,2], as observed in soft x-ray resonant photoemission spectroscopy. Based on \textit{ab initio} calculations and crystal-field analysis of different atomic environments, we identify the origin of this behavior and we argue on the possible origin of the extraordinarily high electron mobility measured in this heterostructure [2].\newline [1] P. Schuetz et al., in preparation.\newline [2] Y. Z. Chen et al., Nature Communications 4, 1371 (2013). [Preview Abstract] |
Wednesday, March 15, 2017 9:12AM - 9:24AM |
K37a.00005: Electronic structure of EuTiO$_{\mathrm{3\thinspace }}$and related heterostructures Anderson Janotti, Zhigang Gui EuTiO$_{\mathrm{3}}$ (ETO) is a complex oxide that displays strong spin-lattice coupling, large magnetoelectric effects, and undergoes a series of structural and magnetic phase transitions when subjected to pressure or epitaxial strain. At very low temperatures, it transforms to an antiferrodistortive tetragonal structure with a G-type antiferromagnetic (AFM) ordering. Several approaches have been presented to tune the magnetic ordering from the G-type antiferromagnetism to ferromagnetism, often relying on external pressure or epitaxial strain. Doping through substitution of trivalent species on the europium site or creation of oxygen vacancies have also been proposed to lead to ferromagnetism. However, the fundamental mechanism by which excess electrons from impurities or defects lead to ferromagnetic ordering is unclear. In this study, we explore the effects of doping on the magnetic ordering in EuTiO$_{\mathrm{3}}$ through first-principles calculations. In special, we discuss how ferromagnetic ordering can be stabilized by means of charge transfer across the interface in polar/nonpolar complex-oxide heterostructures. [Preview Abstract] |
Wednesday, March 15, 2017 9:24AM - 9:36AM |
K37a.00006: Shubnikov-de Haas Oscillations in LaTiO$_3$/SrTiO$_3$ Heterostructures Michael Veit, Brad Ramshaw, Mun Chan, Yuri Suzuki Emergent metallic behavior in heterostructures of the Mott insulator LaTiO$_3$ and the band insulator SrTiO$_3$ was observed for the first time more than a decade ago. It has often been compared to other oxide systems which have a two-dimensional Fermi surface, but there have been few studies probing the dimensionality of the metallicity in this system. We have studied the transport properties of thin films of LaTiO$_3$ on SrTiO$_3$ substrates. Our measurements have indicated that the entirety of the LaTiO$_3$ film is conductive with an additional contribution near the interface. When the film thickness is on the order of 3-4 unit cells, we observe two sets of Shubnikov-de Haas oscillations - low frequency oscillations with a frequency of 2T and high frequency of 36T. We attribute the observation of these two sets of oscillations to a Rashba splitting which creates a smaller inner Fermi pocket and a larger outer Fermi pocket. These results are consistent with our measurements of in plane anisotropic magnetoresistance and a weak antilocalization correction to the magnetoconductance Further measurements on the angular dependence of the oscillations indicate that their frequency does not change, thus indicating that the Fermi surface is more three-dimensional. [Preview Abstract] |
Wednesday, March 15, 2017 9:36AM - 9:48AM |
K37a.00007: Evolution and Control of Electronic Structures near the Interface of Complex Oxide Heterostructure SmTiO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3}}$ Ryo Mori, Patrick Marshall, Brandon Isaac, Jonathan Denlinger, Susanne Stemmer, Alessandra Lanzara The confined electron system in the quantum well of the transition metal oxide, SrTiO$_{\mathrm{3}}$, embedded in the rare earth titanate, SmTiO$_{\mathrm{3}}$, shows unique properties, such as high carrier density, fermi liquid to non-fermi liquid transition, and pseudo-gap, which can be controlled by changing the shape of the quantum well. We will present a distinct difference in the electronic structures between the different quantum well structures obtained by angle-resolved photoemission spectroscopy (ARPES) measurements, suggesting the possibility to control the orbital character and the electron correlation near the interface as well as carrier density. [Preview Abstract] |
Wednesday, March 15, 2017 9:48AM - 10:00AM |
K37a.00008: Evidence for ferromagnetism in NdTiO$_3$/SrTiO$_3$ heterostructures Yilikal Ayino, Peng Xu, Juan Tiger-Lazo, Jin Yue, Bharat Jalan, Vlad Pribiag Complex oxide interfaces are a promising platform for studying a wide array of correlated electron phenomena in low-dimensions, including superconductivity and magnetism. The microscopic origin of these phenomena remains an open question. Evidence for magnetic order at oxide interfaces has been reported using various experimental techniques, including vibrating sample magnetometry, superconducting quantum intereference magnetometry, neutron scattering, and magneto-transport. Hysteresis in magneto-transport can provide evidence for magnetic ordering. Here we investigate electron transport in MBE-grown NdTiO$_3$/SrTiO$_3$ heterostructures as a function of magnetic field and time, at temperatures down to 150 mK. By studying the time-dependence of magnetoresistance (MR) we observe two types of hysteretic features: 1) persistent features, and 2) transient features with a characteristic timescale of ~100 seconds. We attribute the persistent hysteresis to magnetism in the sample. We discuss the importance of time-dependent measurements for distinguishing signatures of magnetism from other effects that can produce hysteretic MR in experiments at low temperatures. [Preview Abstract] |
Wednesday, March 15, 2017 10:00AM - 10:12AM |
K37a.00009: Electric field effect near the metal-insulator transition of a two-dimensional electron system in SrTiO$_{\mathbf{3}}$ Kaveh Ahadi, Omor Shoron, Patrick Marshall, Evgeny Mikheev, Susanne Stemmer We report on the effects of electric field on the two-dimensional electron gas at the SmTiO$_{3}$/SrTiO$_{3}$ interface. Reducing the thickness of the SmTiO$_{3}$ depletes a significant fraction of the two-dimensional electron gas and drives it into the vicinity of a temperature-triggered metal insulator transition (257 K). After gate metal deposition, the sheet resistance exceeds the quantum resistance, $h$/e$^{2}$, and the SrTiO$_{3}$ channel is in the hopping regime at zero gate bias. We show that electric field effect can be used to tune the two-dimensional electron system in SrTiO$_{3}$ that is deep in the insulating phase ($R_{s}$ \textgreater 380 k$\Omega $/$\mathqed )$ to near the transition to a metal, which occurs at the quantum limit, $R_{s}$ \textasciitilde $h$/e$^{2}$. Saturation current densities and sheet resistance modulation cannot solely be explained by carrier density modulation, which was independently confirmed using capacitance-voltage measurements, indicating a change in the nature of transport as a function of electric field. The channel resistances as a function of temperature can all be scaled by a single parameter, which depends on the gate bias, similar to two-dimensional electron systems in high-quality semiconductors. [Preview Abstract] |
Wednesday, March 15, 2017 10:12AM - 10:24AM |
K37a.00010: Disorder and Strong Correlations in Two-Dimensional Electron Liquids in SrTiO$_{\mathrm{3}}$ Patrick Marshall, Honggyu Kim, Susanne Stemmer We report on angle-dependent measurements of the resistances and Hall coefficients of two-dimensional electron liquids in MBE-grown SmTiO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3}}$/SmTiO$_{\mathrm{3}}$ quantum wells on DyScO$_{\mathrm{3\thinspace }}$(001) substrates, which were found to possess highly anisotropic planar defects. The defects lead to strong in-plane anisotropy in the transport properties, allowing for a systematic investigation of the interplay between disorder and the strong correlations that give rise to a number of unusual phenomena in this system. Disorder was found to increase the residuals in the resistance and Hall angle by up to a factor of 11, while the Hall scattering amplitude was unaffected. The Hall angles exhibited strong T$^{\mathrm{2}}$ temperature dependences along all directions, while the longitudinal resistances displayed very different direction-dependent behavior with temperature. This is indicative of carrier-lifetime separation between the longitudinal and Hall scattering rates. Remarkably, the degree of the carrier-lifetime separation was completely insensitive to disorder. [Preview Abstract] |
Wednesday, March 15, 2017 10:24AM - 10:36AM |
K37a.00011: Transport studies and potential fluctuations in mesoscopic-scale SmTiO$_3$/SrTiO$_3$/SmTiO$_3$ quantum wells Will Hardy, Panpan Zhou, Brandon Isaac, Patrick Marshall, Evgeny Mikheev, Susanne Stemmer, Douglas Natelson Heterointerfaces of rare earth titanates comprise an intriguing family of systems with coexisting and competing physical orders. Some examples, such as LaAlO$_3$/SrTiO$_3$, support high carrier density quantum wells whose electronic properties are determined by lattice distortions, spin-orbit coupling, defects, and various regimes of magnetic and charge ordering. Here, we study electronic transport in mesoscale heterostructure devices of SrTiO$_3$ sandwiched between layers of SmTiO$_3$, in which the transport properties can be tuned from a regime of Fermi-liquid like resistivity ($\rho$ $\propto$ $T^2$) to a non-Fermi liquid ($\rho$ $\propto$ $T^{5/3}$) by controlling the STO thickness. Unexpected, large, time-dependent surface potential fluctuations ramp up below 10 K, and are apparently independent of the drive current and contact spacing distance but suppressed with increasing contact size. Magnetoresistance fluctuations are also observed, which are reminiscent of universal conductance fluctuations but not entirely in agreement with their conventional form. Candidate interpretations of the underlying mechanism are discussed in terms of a fluctuating Seebeck coefficient, and in the context of a material system that has a low-T pseudogap and is not necessarily a Fermi liquid. [Preview Abstract] |
Wednesday, March 15, 2017 10:36AM - 10:48AM |
K37a.00012: Two-dimensional electron gas in NaMnF$_{\mathrm{3}}$/SrTiO$_{\mathrm{3}}$ thin films: an \textit{ab}-initio study. WILFREDO IBARRA-HERNANDEZ, ANDRES CAMILO GARCIA-CASTRO, ALDO H. ROMERO Control, by surface techniques of the two-dimensional electron gas (2DEG) in oxide/oxide thin-films and heterostructures [1,2], has been one of the most exciting topics recently studied in surface physics. On the other hand, oxide/fluoride heterostructures are expected to be as interesting as the mentioned counterparts. Moreover, our recent findings on A-site geometrically driven ferroelectricity on NaMnF$_{\mathrm{3}}$ (NMF) under epitaxial strain [3], have motivated experimental efforts to synthesize NMF thin films on SrTiO$_{\mathrm{3}}$ (STO) substrates. We present ab-initio calculations of the electronic and structural properties of these thin-films. We observed the appearance of a 2DEG at the NMF/STO when oxygen or fluorine vacancies are close to the interface. Thin-films without vacancies and intermixing exhibit the appearance of an electric field in STO, in absence of polar-charged layers. This can be explained in terms of the electrostatic potential along the heterostructure induced, and possibly controlled, by the NMF's spontaneous polarization. [1] S. Adhikari, et. al, Adv. Funct. Mater. 26, 5453--5459 (2016) [2] W. Dai, et. al, Nano Lett 16 (4), 2739--2743 (2016) [3] A. C. Garcia-Castro, et. al, Phys. Rev. Lett. 116, 117202 (2016) [Preview Abstract] |
Wednesday, March 15, 2017 10:48AM - 11:00AM |
K37a.00013: Quantum confinement engineering on a novel two dimensional electron gas based on KTaO$_{3}$ oxide interface Ludi Miao, Jing Wang, Renzhong Du, Bailey Bedford, Nathan Huber, Weiwei Zhao, Qi Li The discovery of two-dimensional electron gases (2DEGs) at transition metal oxide (TMO) surfaces and interfaces has opened up broad interest due to their exotic properties such as quantum Hall effect, 2D superconductivity and gate controlled ground states. Recently, 5$d$ TMOs are hotly investigated due to their strong spin-orbit coupling (SOC), a key element of topological materials. Among them, KTaO$_{3}$ (KTO) not only hosts 2DEGs but also involves strong SOC. Here we report the discovery of electron gas based on KTO oxide interface, with low temperature mobility as large as 8000cm$^{2}$V$^{-1}$s$^{-1}$. Strong Shubnikov-de Haas (SdH) oscillation in magnetoresistance is observed at 350 mK. Based on this playground we demonstrate a novel technique to perform quantum confinement engineering by inserting an insulating spacing layer into the interface. Indeed, we observed a drastic change in SdH oscillation from 3D-like behavior to 2D-like behavior. In addition, Fermi surface reconstruction due to the quantum confinement is also observed from SdH oscillation. Our results not only provide a novel playground for condensed matter physics and all-oxide device applications, but also open a promising new route in tailoring the dimensionality of electron gas systems. [Preview Abstract] |
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