Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session S52: Complex Oxide Films, Surfaces, and Interfaces II |
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Sponsoring Units: DCMP Chair: Daniel Dougherty, North Carolina State University Room: Mile High Ballroom 1E |
Thursday, March 5, 2020 11:15AM - 11:27AM |
S52.00001: Symmetry breaking of in-plane anisotropic magnetoresistance with temperature in La-doped Sr2IrO4 film Mingrui Liu, hongxia xue, Jianchao Meng, Ruipeng Bai, Weimin Jiang, Zhe Zhang, Jingzhuo Ling, Lin He, Ruifen Dou, Changmin Xiong, Jiacai Nie Electron-doped Sr2IrO4 has been the subject of recent attention because of its similarities with hole-doped La2CuO4. However, direct evidence of its superconductivity has not yet been observed, which has led to various unresolved issues related to this material. In this study, a 14-nm thick La-doped Sr2IrO4 film was grown on a (001) SrTiO3 substrate. We found that the fourfold component of the in-plane anisotropic magnetoresistance disappears and is replaced by a twofold symmetry as the temperature increases. Variable-temperature x-ray diffraction and spatially resolved optical second-harmonic generation experiments eliminate the possibility of crystal structural distortion. The temperature dependence of direct current magnetization measurements indicates that a change in the spin structure may account for the symmetry breaking, similar to the nematic ordering of iron-based and other superconductors. These provide a perspective on these materials that helps elucidate the nature of magnetic interactions and explores the expected superconductivity of iridates. |
Thursday, March 5, 2020 11:27AM - 11:39AM |
S52.00002: Rock-salt type superconductor/ferromagnet heteroepitaxial junction: LaO/EuO Kenichi Kaminaga, Daichi Oka, HIrofumi Oka, Tomoteru Fukumura We report the first synthesis of rock-salt type superconductor/ferromagnet heteroepitaxial junctions using ferromagnetic semiconductor EuO [1]. As the superconducting layer, we deposited LaO with the maximum Tc of 5.2 K onto EuO. The small lattice mismatch made it possible to synthesize a high-quality heteroepitaxial junction with an atomically sharp interface that realizes the ideal magnetic proximity effect. The magnetization of LaO/EuO heteroepitaxial junctions was governed by the ferromagnetic EuO layer. The saturation magnetization of 7 μB/Eu atom at 5 K was equivalent to that of EuO thin film. Owing to the sharp interface and the strong magnetization, superconductivity in 21 nm thick LaO layer was fully suppressed by only 6 nm thick EuO layer. This system can be used for a new heteroepitaxial platform of superconducting spintronics devices. [1] K. Kaminaga et al., Chem. Lett. 48, 1244 (2019). |
Thursday, March 5, 2020 11:39AM - 11:51AM |
S52.00003: Growth and electronic structure of LTO/STO heterostructure: Multi-modal studies Hawoong Hong, Friederike Wrobel, XI YAN, Anand Bhattacharya, Dillon Fong LTO/STO interfaces have interesting features including 2-DEG, superconductivity and magnetism. These systems may realize complex-oxide based electronic devices. LTO is supposed to be insulators. However, PLD produced films, under compressional stress, behave like metal. It also undergoes transition to a Mott insulator below -145° C. Advanced photon source has beamlines suited for complex oxide studies. Sector-33 oxide-MBE allows operando studies of x-ray diffraction and RHEED measurements during the growth of oxide films. One can also transfer the sample in a UHV vacuum suitcase to soft-xray ARPES station at the beamline 29. Soft-xray ARPES provides significant enhancement in the penetration depth and one can study the interfaces in addition to the surfaces of samples. Deposition by alternating lanthanum and titanium did not produced pure phase of LaTiO3. Interestingly, the 6 unit cell sample from alternating deposition showed 2-DEG features in ARPES. LaTiO3 films could be successfully produced through codeposition of lanthanum and titanium. However, x-ray diffraction measurements showed the films from codeposition easily became rough after the growth. |
Thursday, March 5, 2020 11:51AM - 12:03PM |
S52.00004: Coherent lattice motion in freestanding perovskite films probed by ultrafast electron diffraction Yifan Su, Alfred Zong, Anshul Kogar, Di Lu, Seung Sae Hong, Harold Hwang, Nuh Gedik Advances in femtosecond lasers make it possible to coherently generate specific phonon modes in crystals. These coherent lattice vibrations enable one to pinpoint specific atomic motion on the picometer scale, and this knowledge, in turn, helps one to realize ultrafast control of material property by laser pulses. In this experiment, we performed ultrafast electron diffraction on a 20-nm freestanding film of La0.67Ca0.33MnO3. Following photoexcitation, we observed a 0.15 THz acoustic phonon extracted from Bragg peak intensity, position and width. By tracing the coherent oscillations in these three channels for more than 20 Bragg peaks, we are able to reconstruct in real space the unconventional atomic trajectory following the arrival of the laser pulse. |
Thursday, March 5, 2020 12:03PM - 12:15PM |
S52.00005: Stoichiometry-Dependence of Electronic Properties in LaVO3 Thin Films BIWEN ZHANG, Jade Holleman, Yan Xin, Stephen A McGill, Christianne Beekman LaVO3 (LVO) has been proposed as a promising material for photovoltaics because its strongly correlated 3d electrons can facilitate creation of multiple electron-hole pairs per incoming photon, which would lead to increased device efficiency. Our group grows thin films of LVO on SrTiO3 substrates using pulsed laser deposition. We control the La:V ratio of the films from ~60:40 to ~40:60 by adjusting laser fluences. We find that while V-rich films show behaviors that are similar to bulk LVO, films that are La-rich show remarkable differences in optical measurements, and more rich temperature dependent transport behaviors, which indicates the presence of electronic phase separation. This study allows us to better understand the complex physical properties of strongly correlated insulators paving the way for their use as absorbers in high performance photovoltaics. |
Thursday, March 5, 2020 12:15PM - 12:27PM |
S52.00006: Oxygen vacancy induced electronic phenomena of KTaO3 Shashank Kumar Ojha, Sanat Kumar Gogoi, Manish Jain, Srimanta Middey Emergent two-dimensional electron gas (2-DEG) at complex oxide interfaces has been a subject of huge interest over the last fifteen years. The discovery of 2-DEG at the interface between LaAlO3 and SrTiO3 has lead to a massive search for other 2-DEG systems. Various mechanisms viz. polar catastrophe, cationic intermixing and oxygen vacancy have been proposed to explain the origin of interfacial conduction. Since more than one mechanism can be operative simultaneously, well-defined understanding remains a challenge. In this work, we report on sole effect of oxygen vacancy on electronic structure modification of a prototypical perovskite KTaO3 by deliberately creating oxygen vacancies in a pristine single-crystalline sample. Oxygen deficiency turns KTaO3 into a metal which shows many interesting quantum transport phenomena such as Shubnikov-de Haas oscillations, anomalous Hall effect. Ab-initio calculations find the existence of vacancy induced local magnetic moments on Ta around vacancy and the skew scattering of conduction electrons by these local moments lead to the observation of anomalous Hall effect. |
Thursday, March 5, 2020 12:27PM - 12:39PM |
S52.00007: Effect of Growth Conditions on the Formation of a 2-Dimensional Electron Gas at Antiferromagnetic LaCrO3 /SrTiO3 Interfaces Athby Al-Tawhid The realization of a high mobility two-dimensional conducting interface between a polar anti-ferromagnet, LaCrO3 (LCO) and non-polar SrTiO3 (STO) has important implications for the interfacial coupling of electronic and magnetic degrees of freedom. To realize such an interface, we examine the effect of growth conditions and post growth treatment on the structural and electronic properties of the polar/non-polar(LCO/STO) interfaces. Growth at high temperatures and low oxygen partial pressure followed by post growth annealing in Oxygen results in a 2-dimensional electron gas(2-deg) at the interface. The dimensionality of the conducting layer is confirmed by electric and magneto transport measurements. Growth at a lower temperature or higher partial oxygen pressure leads to an insulating interface. High-resolution synchrotron X-ray-based structural determination of the atomic-scale structures of both metallic and insulating LCO/STO interfaces shows structural differences between the two cases attributed to competing mechanisms present to alleviate the interfacial polar discontinuity. |
Thursday, March 5, 2020 12:39PM - 12:51PM |
S52.00008: Interfacial mechanical coupling at the interface of Pb0.2Zr0.8TiO3/LaNiO3/SrTiO3 heterostructures Claudia Lau, Cristina Visani, Stephen Albright, Zhan Zhang, Ankit Disa, Divine Kumah, Charles H Ahn, Frederick J Walker The coupling of ferroelectric polarization to thin films of the conducting oxide LaNiO3 results in large changes of conductivity at an epitaxial ferroelectric-LaNiO3 interface. The observed changes in conductivity are larger than what is expected from band theory, implying the importance of electronic and structural correlations. To characterize the structural changes at the interface, specially designed capacitor structures are fabricated from thin films of PbZr0.2Ti0.8O3 deposited on epitaxial LaNiO3. The device geometry is optimized for in operando synchrotron x-ray diffraction measurements of crystal truncation rods in order to identify the atomic-scale structural changes responsible for the changes in conductivity. These structural changes include rotations of the LaNiO3 oxygen octahedra, which are characterized via measurement of half-order Bragg peaks. The octahedral rotations exhibit a hysteresis loop as the applied voltage is swept through the coercive field of the ferroelectric and are correlated with the conductivity of the channel, with larger rotations leading to reduced conductivity. |
Thursday, March 5, 2020 12:51PM - 1:03PM |
S52.00009: Zero-Bias Anomalies Observed in the Tunneling Spectra of Sr3(Ru0.84Mn0.16)2O7 Yifan Yang, Mingming Fu, Qiang Zou, Rongying Jin, Zheng Gai, Jiandi Zhang, E Ward Plummer The partial substitution of Mn for Ru in the bilayer ruthenate Sr3(Ru1-xMnx)2O7 stabilizes long-range antiferromagnetic (AFM) ordering with the highest transition temperature TN= 82 K for x = 0.16 [1]. Here, we report the observation of a well-defined symmetric zero-bias anomaly (ZBA) at 5.2 K in the scanning tunneling spectroscopy (STS) of x = 0.16. The temperature dependence of the ZBA shows thermal broadening and does not correlate with the bulk AFM transition. Consistent with this observation, there is no change in the ZBA with the application of a magnetic field (9T). This is in contrast to the case for x = 0, in which the ZBA is asymmetric about zero bias and magnetic field dependent which gradually vanished at 11T [2]. The more symmetric and narrower ZBA in x = 0.16 could originate from the distinct surface properties [3]. We will discuss the relationship between doping (disorder), the surface properties, and ZBA. |
Thursday, March 5, 2020 1:03PM - 1:15PM |
S52.00010: Tuning the electronic properties of the 4d transition metal oxide LaRhO3 Juan Jiang, TaeKyun Lee, Sangjae Lee, Sohrab Ismail-Beigi, Frederick J Walker, Charles H Ahn Perovskite transition metal oxides exhibit various novel properties due to strong correlations among their d electrons. These correlation effects are well known in the 3d transition metal oxides, such as LaCoO3, where multiple spin states can be observed. Electronic correlations are expected to change as the transition metal is changed from a 3d element to a 4d element in the same column of the periodic table, for example changing from Co to Rh. To explore these changes, we grow epitaxial La1-xSrxRhO3 thin films with Sr concentrations as large as 50% using molecular beam epitaxy. Hall measurements show a sign change from hole-like conduction for low doping to electron-like conduction for a large doping level of x=0.3. Systematic changes in electronic structure as a function of doping are predicted by theory and may provide a basis for understanding electronic correlations in transition metal oxides. |
Thursday, March 5, 2020 1:15PM - 1:27PM |
S52.00011: Engineering Coercivity of SrRuO3 thin film by SrTiO3 capping layer Eun Kyo Ko, Junsik Mun, Han-Gyeol Lee, Jinkwon Kim, Miyoung Kim, Lingfei Wang, Tae Won Noh Oxide heterostructures have has a high potential for spintronics applications due to their well-defined heterointerfaces and vast functionalities. Understanding and utilizing the advantages of oxide spintronics requires effective control of magnetism, such as engineering coercivity (HC). SrRuO3 (SRO) is an itinerant ferromagnet with high tunable electron-electron correlation and spin-orbit coupling. It could be a good candidate for exploring spintronics applications due to the recently discovered exotic topological properties. [1, 2] |
Thursday, March 5, 2020 1:27PM - 1:39PM |
S52.00012: Effects of Tungsten Doping on Magnetic and Material Properties of VO2/Ni Bilayers Logan Sutton, Jose De La Venta, Joshua P Lauzier Magnetic hybrid materials show increasing promise as candidates for magnetic storage and magnetic sensors under a wide range of operating environments. Strain coupled materials are a type of magnetic hybrid materials that show a strong potential for precise control over magnetic properties. Vanadium oxides are a class of compounds which have structural phase transitions (SPTs) at various temperatures, making them ideal candidates in the fabrication of hybrid materials of this nature. Previous work has shown sputtered vanadium oxide/ferromagnetic bilayers have large changes in magnetization and coercivity at the vanadium oxide transition temperature. In this study, a sol-gel synthesis technique was used to fabricate W-doped VO2/Ni bilayers. Doping with W allows for the VO2 transition temperature to be lowered in an easily controlled manner, making it more viable for various applications. The effects of this doping technique on the material and magnetic properties of the VO2 layers are investigated. We find a stabilization of the rutile phase of VO2, and formation of V2WO6. VO2/Ni bilayers show a sharp decrease in the coercivity and increase in the magnetic moment at the VO2 SPT. W doping decreases the temperature of these magnetic effects and also decreases their magnitude. |
Thursday, March 5, 2020 1:39PM - 1:51PM |
S52.00013: Pulsed-laser epitaxy of metallic delafossite PdCrO2 Jong Mok Ok, Matthew Brahlek, Woo Seok Choi, Kevin Roccapriore, Matthew F Chisholm, Gaurab Rimal, Soyeun Kim, Changhee Sohn, Elizabeth Skoropata, Seongshik Oh, Ho Nyung Lee Within the metallic ABO2 delafossites, the natural heterostructuring among the A-layers, that are highly-conductive and 2-dimensional, with the triangular and localized nature on the BO2 is a basic platform for many interesting phenomena. Thin film growth of these materials can enable both tuning basic properties as well as giving new insight into the novel phenomena found in this class of materials, yet this has proven extremely challenging. Here, we report the epitaxial growth of the metallic delafossite PdCrO2 by pulsed laser deposition (PLD) across many different substrates and epitaxial buffer layers and growth conditions. This work has revealed the fundamental role PLD-growth conditions, epitaxial strain, and chemical and structural character of the substrate play in stabilizing the growth of PdCrO2. It is found that a low-strain delafossite buffer layer is required to stabilize PdCrO2. The resulting films are commensurately strained, show very narrow rocking curve widths as low as ~0.1°, and show an antiferromagnetic transition at 40 K that persists down to as thin as 3.6 nm. This works provides key insight for the growth of the boarder class of metallic delafossites and will enable tuning the basic properties of these interesting materials. |
Thursday, March 5, 2020 1:51PM - 2:03PM |
S52.00014: Growth of metallic delafossite PdCoO2 by molecular beam epitaxy Matthew Brahlek, Gaurab Rimal, Jong Mok Ok, Debangshu Mukherjee, Alessandro Mazza, lu Qiyang, Ho Nyung Lee, Thomas Zac Ward, Raymond Unocic, Gyula Eres, Seongshik Oh The ABO2 delafossite oxides are a unique class of oxides with layered A-BO2-A-BO2 structure with inplane trigonal coordination. Here, we report successful growth of the metallic delafossite PdCoO2 by molecular beam epitaxy (MBE) [1]. The key challenge is controlling the oxidation of Pd in the MBE environment where phase segregation is driven by the reduction of PdCoO2 to cobalt oxide and metallic palladium. This is overcome by combining low-temperature atomic layer-by-layer MBE growth in the presence of reactive atomic oxygen with a postgrowth high-temperature anneal. Thickness dependence (5-265 nm) reveals that in the thin regime (<75 nm), the resistivity scales inversely with thickness, likely dominated by surface scattering; for thicker films, the resistivity approaches the values reported for the best bulk crystals at room temperature, but the low-temperature resistivity is limited by structural twins. This work shows that the combination of MBE growth and a postgrowth anneal provides a route to creating high-quality films in this interesting family of layered, triangular oxides. |
Thursday, March 5, 2020 2:03PM - 2:15PM |
S52.00015: Molecular Modeling of the Adsorption-Induced Expansion of Graphene Oxide Frameworks Todd N. Lombardi, Joseph Schaeperkoetter, Alberto Albesa, Carlos Wexler Adsorbent materials such as activated carbons (AC) have potential for gas storage or separation. ACs are often modeled as slit-shaped pores: parallel graphene-like sheets of very high surface area. In almost all adsorption analyses adsorbent is assumed structurally inert. It has been long known that liquids adsorption produces structural deformations. More recently gate opening transitions have been observed in Metal Organic Frameworks during subcritical adsorption of gases. The deformation arises from large solid-liquid interactions and depend on the nature of the adsorbent-adsorbate interaction, sometimes contracting or expanding. More recently, a monotonic increase ~4% in the d-spacing of benzene diboronic acid (DBA) Graphene Oxide Frameworks (GOF) was observed by in situ neutron diffraction during supercritical adsorption of various gases [1]. We present the results of molecular dynamics simulations based on ab initio models of GOFs. Our results suggest that a model of randomly oriented covalently bonded DBA linkers is consistent with experimental observations. |
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