Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session YY07: V: Complex Oxide Interfaces |
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Sponsoring Units: DMP Chair: Nini Pryds, Tech Univ of Denmark Room: Virtual Room 7 |
Wednesday, March 22, 2023 10:00AM - 10:12AM |
YY07.00001: Emergent magnetic properties at 2D material/hexagonal oxide interface M J Swamynadhan, Saurabh Ghosh, Andrew O'Hara, Sokrates T Pantelides It was recently found that collinear or non-collinear magnetic moments can be induced in monolayer or few-layer 2D materials by magnetic bulk substrates. For example, it was shown that Dzyaloshinskii-Moriya interaction (DMI), which are responsible for spin canting in materials, are induced in 2D layers by a Co substrate. The hexagonal phase of LuFeO3 (h-LFO) is multiferroic with a huge out-of-plane polarization and strong DMI, whereby h-LFO is a suitable material for such heterostructures. In this work we explore possible emergent multifunctionality in 2D polar materials like MnSSe (Janus structure), grown on h-LFO and Hf doped h-LFO. We previously showed that Hf doping can tune the magnetism between non-collinear and collinear spin configurations by tuning its DMI. Hence, the resulting 2D-material/h-LFO may lead to induction of DMI in the 2D layer with potential for other interesting magnetic properties. The goal is to design a heterostructure with tunable magnetic spin configurations by tuning the polarization of the substrate and the 2D material. Tuning and switching the polarization of h-LFO and Hf-doped h-LFO affects the DMI and Magnetic anisotropy energy (MAE) of the polar 2D material, which can lead to tuneable magnetic skyrmions on the 2D materials. |
Wednesday, March 22, 2023 10:12AM - 10:24AM |
YY07.00002: Generation of new ferroelectric domains in PbTiO3/SrTiO3 superlattices Fernando Gómez-Ortiz, Pablo Garcia-Fernandez, Juan M. López, Javier Junquera We investigate via second principles simulations the electrostatics of multi-domain structures in (PbTiO3)n/(SrTiO3)n superalttices. The relaxed structure corresponds to a polar vortex configuration where counter-rotating vortices lay in between of the c-domains. It is observed that the optimal value of the domain width w, follows diophantically Kittel law for a thickness n assuming straight domains. However, stabilization of other widths different from the optimal are possible within a given range. Studying these limiting cases we could observe that the mechanism for the destruction of domains is the progressive approach of the vortices towards the interface driving the system to a polarization wave directed along x-direction. More interestingly, the generation of new c domains is driven by the nucleation of small polarization regions at the interfaces being encapsulated by pairs of counter-rotating vortices. Moreover, following the dynamics of such structures we detect that the recombination of vortex-antivortex pairs serves as the growth mechanism for the closure and stabilization of the emergent domains |
Wednesday, March 22, 2023 10:24AM - 10:36AM |
YY07.00003: Influence of misfit dislocations on oxygen vacancy migration at SrTiO3/BaZrO3 heterointerfaces William J Ebmeyer, Pratik P Dholabhai Mismatched complex oxide heterostructures and thin films have remarkable promise for next-generation electrolytes in solid oxide fuel cells (SOFCs), wherein misfit dislocations impact interfacial ionic transport. Nevertheless, fundamental understanding of atomic scale structure of misfit dislocations and their influence on oxygen vacancy migration at functional interfaces is lacking. For SrTiO3/BaZrO3 heterostructure, we employed atomistic simulations to predict the thermodynamic stability and atomic scale structure of misfit dislocations, which is found to depend on interface layer chemistry. Using high-throughput simulations, thousands of activation energy barriers were determined for oxygen vacancy migration at different interfaces. Higher activation energies are observed in the vicinity of dopants, whereas migration paths near misfit dislocation lines are lower in energy, but vary somewhat depending on interface chemistry. This data is currently being utilized to develop a kinetic lattice Monte Carlo model for tracing oxygen vacancy diffusion at oxide interfaces. Results on oxygen ion migration at oxide heterointerfaces offer new opportunities to unravel the untapped potential of thin film SOFC electrolytes. |
Wednesday, March 22, 2023 10:36AM - 10:48AM |
YY07.00004: Near infrared to visible intersubband transitions in all-oxide quantum wells using BaSnO3 Suyeong Jang, Stefan Zollner, Wente Li, Alexander A Demkov, Agham Posadas, Yoshitha Hettige Quantum wells (QWs) are made up of a larger bandgap “barrier” material sandwiching the smaller bandgap “well” material. Recently, QW structures using metal oxides such as SrTiO3 (STO)/LaAlO3 have been reported. They boast a rather large conduction band offset of ~2.3eV but suffer from STOs large effective mass. On the other hand, BaSnO3 has a small effective mass(m*BSO =0.2me ) that allows for larger spacing of the QW energy levels. BaSnO3 also, has very high mobility (150cm^2(Vs)^-1) and a wide bandgap (~3.1eV) making it a great candidate in applications calling for transparent conductive films. We will discuss MBE-grown Al2O3/BaSnO3 quantum wells demonstrating a high level of confinement. However, growing Al2O3/BaSnO3 multi-quantum structure in this materials system has proven to be challenging. We demonstrate that the problem can be resolved using MgO instead of Al2O3 as a “barrier” material and BaSnO3 (BSO) as a “well” material. The metal oxide quantum wells allow intersubband transitions from visible to infrared range enabling many applications. |
Wednesday, March 22, 2023 10:48AM - 11:00AM |
YY07.00005: Crystalline and Polarization Orientation Control of BaTiO3 Thin Films on SrTiO3 -buffered Si for Electro-Optic Applications Marc S Reynaud, Huaixun Huyan, Chaojie Du, Wente Li, Agham Posadas, Xiaoqing Pan, Alexander A Demkov Recent research has shown that BaTiO3 thin films epitaxially grown on Si are capable of a large electro-optic response via the Pockels effect crucial for fabricating efficient phase modulators in silicon-integrated photonics. However, the orientation dependence of BaTiO3 for most films yields a dead layer (a region of the film with low electro optic response) for most device geometries. We report on a Si-on-insulator integrated film stack including a buffer layer that effectively negates this region from existing. The film’s quality is confirmed with crystalline characterization and electro-optics measurements showing a response of about 85 pm/V which indicates that this system is a beneficial addition to the field of Si photonics. |
Wednesday, March 22, 2023 11:00AM - 11:12AM |
YY07.00006: Dynamic processes in strontium cobaltite bilayer thin films driven by oxidation and reduction Jill K Wenderott, Eric M Dufresne, Yan Li, Hui Cao, Supratik Guha, Dillon D Fong Transition metal oxides (TMOs) possess variable oxygen stoichiometry which can be the cause of distinct changes to physical and electronic properties. One such TMO, strontium cobaltite (SrCoOx), has two structurally and electrically distinct phases – the insulating orthorhombic brownmillerite (SrCoO2.5 – BM-SCO) and conducting cubic perovskite (SrCoO3-δ – PV-SCO) – that reversibly transition via a topotactic pathway with the insertion or removal of oxygen. In the thin film form, this topotactic transition occurs while preserving high quality epitaxial films, making this material system of interest for resistive memory switching applications. Here, BM-SCO/PV-SCO (001) (15 nm/15 nm) heterostructures on strontium titanate (STO) (001) are investigated in order to understand changes to the interface between the two phases under oxidizing and reducing conditions. X-ray diffraction (XRD) and X-ray photon correlation spectroscopy (XPCS) studies reveal oxidizing conditions coupled with heating to ~250 °C led to measurable dynamics associated with changes to the PV-SCO phase as it accommodates oxygen into its lattice. Understanding gleaned from the nature and dynamics of these processes are relevant to the development of more controlled switching in these epitaxial heterostructure devices. |
Wednesday, March 22, 2023 11:12AM - 11:24AM |
YY07.00007: Theoretical investigation of octahedral tilting and bandgap non-linearity in monolayer Ruddlesden–Popper A2Pb1-xGexI4 perovskites: A GGA(PBE)+SOC level study Mehreen Javed 2D Ruddlesden-Popper (RP) perovskites (R-NH3)2An-1BnX3n+1 with tailorable photovoltaic features of low toxicity, reduced dimensionality, and defect tolerance hold promise to overcome the main constraints of perovskite solar cells (PSCs). A systematic investigation of the structural and electronic properties of pure and mixed (R-NH3)2Pb1-xGexI4 systems, was performed with and without spin-orbit coupling (SOC), by using density functional theory (DFT). The organic spacer cations (R-NH3+)2 of Methylammonium (MA-CH3NH3+) and Phenylethyl ammonium (PEA-C6H5(CH2)2NH3+) with x=0.0, 0.25, 0.50, 0.75, 1.0, resulted in the compositionally modified 32-permutations by systematically substituting the inorganic cations. Short-range ordering has categorized all studied compositions of (R-NH3)2Pb0.50Ge0.50I4 into column and battenberg schemes depending on the Ge defect site. The competing effects of octahedral tilting and lattice distortion with bandgap bowing and spin-orbit coupling, across Pb-Ge compositional systems, provide a systematic strategy to tune bandgaps. By controlling the cations’ composition, these mixed 2D-perovskites outlined the strategy to achieve the desired bandgap and band positions. A rational design approach of low dimensional perovskites was adopted to tune the electronic properties through the spacer and inorganic cation engineering. Our findings expose the scope of monolayer-based systems as an ideal choice of absorber for the bottom sub-cell in all-perovskites 2D-3D tandem solar cell, harvesting light from visible (2.4 eV) up to infrared (1.2 eV) in the solar spectrum with features of defect tolerance, quantum and dielectric confinement, low bandgap, low effective masses, and high mobility. |
Wednesday, March 22, 2023 11:24AM - 11:36AM |
YY07.00008: Role of Rare earth doping on scintillation enhancement in yellow emitting KZnF3 nano cubes Navadeep Shrivastava, Zhiping Luo, Thomas Murray, Burak Guzelturk Herein, we report the KZnF3 nanocubes as one of the candidates to get Ce3+ doping and down conversion phenomenon under UV photon excitation as well as energetic x-rays to its low phonon energy and unique crystal structure. The hydrothermal method involving aqueous and organic solvents (ethanol and oleic acid) was used to prepare the synthesis of the doped KZnF3 nanoparticlesKZnF3 belongs to the cubic perovskite structure with the <!--[if gte msEquation 12]>p m:val="¯"/> style='mso-bidi-font-style:normal'>m style='mso-bidi-font-style:normal'>3m space group (no. 221) showing crystallite sizes around 60 nm by X-ray diffraction and doping of Ce3+ up to 2% was found to be consistent with the crystal structure. Transmission electron microscopy suggested the cube-like morphology of nanoparticles with average size distribution around ~ 50 nm and energy dispersive spectroscopy confirmed the uniform distribution of elements. FTIR analysis confirmed the adsorption of the oleic acid ligands on the surface of the nanoparticles. The UV excitation (254 nm) of the undoped KZnF3 nanocubes showed the yellow luminescence centered at 582 nm, whereas the doping of Ce3+ improved the intensity around 580 nm and displayed a very week broad band emission around 350 nm due to f-d transition in Ce3+ ion. Further, undoped and doped KZnF3 nanoparticles were excited by x-ray energies which showed the hot yellow emission band around 580 nm suggesting a huge energy transfer under high energy radiation. The Ce3+ doped specimen, like photoluminescence data, showed two components of emission 340 nm due to Ce3+ and enhanced 580 nm due to matrix. Additional emission intensity stability test under maximum x-ray flux for 10 minutes showed the stable emission without degradation. The strong room temperature emission at 580 nm and week emission at 340 nm further promotes the exploration of different doping based KZnF3 nanocubes for a wide variety of applications including displays, solar energy, catalysis and bioimaging etc. and making the example an interesting candidate for x-ray scintillation applications. |
Wednesday, March 22, 2023 11:36AM - 11:48AM |
YY07.00009: Interplay of frustration, strain and phase co-existence in the mixed valent hexagonal iridate Ba3NaIr2O9 Charu Garg, Antonio Cervellino, Sunil Nair Geometrically frustrated magnets- where triangular lattice antiferromagnets (TLAFs) are considered to be an archetype- remain at the forefront of contemporary condensed matter. Of particular interest in recent years have been a number of Ruthenium and Iridium based perovskite. In this talk, we will discuss the structure-property relationship in the mixed valent geometrically frustrated triple perovskite iridate Ba3NaIr2O9 using detailed synchrotron diffraction, magnetization, thermodynamic and transport measurements. In contrast to what is expected from purely structural considerations, this system stabilizes in a high symmetry hexagonal symmetry at room temperatures. On reducing the temperature, the lattice prefers to be strained rather than distort to a low symmetry phase, as is the norm in this family of materials. Though a low symmetry orthorhombic phase is nucleated below 50 K, this conversion is only partial and the high symmetry hexagonal structure remains the dominant one down to the lowest measured temperatures. Magnetic measurements indicate an extended co-operative paramagnetic regime, which finally freezes to a cluster glass-like phase at very low temperatures. This makes an interesting addition to the family of triple perovskite iridates where complex interplay between lattice strain and structural phase co-existence arises as a consequence of a number of competing energy scales. |
Wednesday, March 22, 2023 11:48AM - 12:00PM |
YY07.00010: Compositional Study of Low Damping Epitaxial Lithium Aluminum Ferrite Films Daisy O'Mahoney, Sanyum Channa, Xin Yu Zheng, Yuri Suzuki The development of ferromagnetic insulators with ultra-low damping and perpendicular magnetic anisotropy (PMA) is of great interest for the study of spin wave-based phenomena, as well as for application in spin wave spintronics. Recently, we have developed epitaxial thin films of the ferrimagnetic spinel structure Li0.5(Al,Fe)2.5O4 (LAFO) with ultra-low magnetic damping. In this talk, we present the study of the effect of composition on the magnetic properties of LAFO by varying the Fe concentration, examining Li0.5Al(0.5)Fe(2.0)O4 (LAFO2.0) and Li0.5Al(1.0)Fe(1.5)O4 (LAFO1.5) films. Both compositions exhibit good epitaxy and excellent crystallinity on single crystal (001) oriented MgAl2O4 (MAO) substrates. X-ray diffraction indicates that both compositions are compressively strained in-plane, although to a lesser degree for LAFO1.5 as it has a smaller lattice parameter from higher Al doping. Static magnetometry reveals LAFO2.0 has disproportionately high saturation magnetisation of 200kA/m, more than twice that of LAFO1.5, suggesting a more detailed investigation of the Fe site distribution is in order. Both compositions show a low Gilbert damping parameter on the order of ~ 7x10-4 for films 10-15nm thick in broadband ferromagnetic resonance (FMR). Stabilizing epitaxial, low damping LAFO films with variable composition, strains and magnetic properties make them promising for future spin wave spintronics applications. |
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