Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E55: Magnetic and Structural Coupling Across Perovskite Interfaces and SuperlatticesFocus Live
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Sponsoring Units: DMP GMAG Chair: Shyam Dwaraknath, Lawrence Berkeley National Laboratory |
Tuesday, March 16, 2021 8:00AM - 8:12AM Live |
E55.00001: Propagation Control of Octahedral tilt in Atomically Designed Oxide Heterostructures Seung Gyo Jeong, Gyeongtak Han, Sehwan Song, Taewon Min, Ahmed Yousef Mohamed, Sungkyun Park, Jaekwang Lee, Hu Young Jeong, Young-Min Kim, Deok-Yong Cho, Woo Seok Choi Designing of oxide heterostructure is a promising pathway for studying the emergent functional properties of transition metal oxides, including metal-insulator transition, spin-phonon coupling, and topologically nontrivial phases. In particular, customization of octahedral bonding geometry plays an essential role in tailoring the functionalities owing to its strong correlation to charge, spin, and orbital degrees of freedom. |
Tuesday, March 16, 2021 8:12AM - 8:24AM Live |
E55.00002: Emergent Structural and Vibrational Properties in SrTiO3-CaTiO3 Superlattices using Atomic-resolution Microscopy and Theory Eric Hoglund, Jordan A Hachtel, Thomas E Beechem, De-Liang Bao, Zachary T Piontkowski, Joshua Caldwell, Jon F Ihlefeld, Jayakanth Ravichandran, Andrew O'Hara, Joseph R Matson, Ramamoorthy Ramesh, Sokrates T Pantelides, Patrick E Hopkins, James M Howe Perovskite oxides offer an abundance of properties with technological importance that are tunable by creating superlattices (SLs). Most research so far focuses on electronic properties, but such SLs can also feature unique thermal properties, which are dictated by lattice vibrations [1]. Here we combine atomic-resolution scanning-transmission-electron microscopy, vibrational electron energy-loss spectroscopy, and density-functional-theory calculations to probe the phonon spectra of a series of SrTiO3-CaTiO3 SLs with 1 to 27 unit-cells per layer. We show large-period SLs feature bulk plus localized interface vibrational modes. As layer thickness decreases, the bulk modes disappear while the interface modes underpin an emergent phonon structure, which is also reflected in the macroscopic vibrational response. This behavior correlates to period thickness reaching the length scale of octahedral coupling at the interfaces, thus reflecting the dominant role of interfaces as size decreases and the need for spatially quantified structural and vibrational data to enable complete understanding of SL behavior. |
Tuesday, March 16, 2021 8:24AM - 8:36AM Live |
E55.00003: Strain-tuned properties of hybrid improper ferroelectric superlattices through first-principles calculations and machine learning Monirul Shaikh, Madhusudan Karmakar, Saurabh Ghosh We have performed first-principles density functional theory (DFT) calculations and machine learning (ML) to investigate the effect of biaxial strain on ferroelectric and magnetic properties of hybrid improper ferroelectric (LaFeO3)1 /(LnFeO3)1 superlattices (SL) where Ln= La-Lu and Y. In Pnma symmetry trilinear coupling between three phonon modes described as F ~ α QT QR QP (where α is the coupling coefficient and QT, QR and QP are tilt, rotation of BO6 octahedra and polar distortion, respectively), establishes the polar space group and non-cancelation of the layered polarization give rise to net polarization. Here, we have discovered a recipe to calculate coupling coefficients between the participating modes and discussed the effect of strain on the coupling constants. We report that strain can enhance the polarization considerably and can change the easy magnetization axis. Finally, using ML, we have predicted the change in polarization upon strain. Our prediction of change in polarization by ML is in excellent agreement with the DFT calculations (Ref. Monirul et. al., Phys. Rev. B 101, 054101(2020)). |
Tuesday, March 16, 2021 8:36AM - 9:12AM Live |
E55.00004: Effect of interfaces on band hybridization, orbital polarization, and helical magnetism in SrFeO3/CaFeO3 heterostructures Invited Speaker: Steven May The alkaline earth ferrates exhibit an array of interesting physical phenomena such as metal-insulator transitions, strong Fe-O covalency, rapid redox reactions, and helical magnetism. In this talk, I will present how the Fe-O band hybridization and Fe 3d orbital occupancy changes across interfaces in isoelectronic SrFeO3/CaFeO3 superlattices. A consequence of the strong hybridization in these materials is that their electronic configuration can be described as containing both d4L0 and d5L1 contributions, where L indicates a ligand hole. Using resonant soft x-ray reflectivity, we find a modulation of the Fe-O hybridization across the superlattice with SrFeO3 hosting a larger ligand hole density than CaFeO3.[1] We show that the Fe eg orbital polarization is correlated with the degree of d4L0 electronic character present in the layers. Results will also be presented on the stability of the helical magnetic order in (CaFeO3)20/(SrFeO3)n superlattices. Using resonant x-ray diffraction, we show that the helical magnetic order coherently propagates through superlattices with n = 1 but does not extend through the SrFeO3 layer in a superlattice with n = 6.[2] We describe these results in context of recently reported multi-q helimagnetism in SrFeO3, while our results support single-q helimagnetism in CaFeO3. |
Tuesday, March 16, 2021 9:12AM - 9:24AM Live |
E55.00005: Controlling spin-polarized carriers at the SrTiO3/EuO interface via the ferroelectric field effect Wente Li, Alexander Demkov Using first principle calculations, we investigate the magneto-electric field effect at the SrTiO3/EuO interface in the BaTiO3/SrTiO3/EuO heterostructure. The spontaneous polarization in tetragonal BaTiO3 is demonstrated to control the movement of the two-dimensional electron gas in SrTiO3 across the interface with ferromagnetic EuO as well as induce spin polarized two-dimensional hole gas and influence the electronic structure at this interface. We also investigate the effect of oxygen vacancy in SrTiO3 near the SrTiO3/EuO interface. To investigate the ferroelectric polarization morphology, we use the phenomenological Landau-Khalatnikov model and compare it with the results of first principle calculations. |
Tuesday, March 16, 2021 9:24AM - 9:36AM Live |
E55.00006: Anomalous magnetoresistance due to longitudinal spin fluctuations in a Jeff = 1/2 Mott semiconductor Lin Hao, Zhentao Wang, Junyi Yang, Derek J Meyers, Jiun-Haw Chu, Mark Dean, Cristian Batista, Jian Liu While manipulation of antiferromagnetic (AFM) order arises to the forefront of spintronics, fluctuation of AFM order is a long-standing problem lying at the heart of correlated electron physics. By engaging with staggered magnetic field effect (STMF), the AFM fluctuation can be manifested as a set of emerging quantum phenomena [Nat. Phys. 14, 806 (2018)]. Here we will present the observation of a positive magnetoresistance that probes the staggered susceptibility of a Jeff = 1/2 Mott semiconductor, which is built as a strong spin-orbit coupled SrIrO3/SrTiO3 superlattice [Phys. Rev. Lett. 119, 027204 (2017)]. This magnetoresistance is particularly large in the insulating paramagnetic phase near the Néel transition. We illustrate its origin of a collective charge response to the large longitudinal spin fluctuations due to the STMF. This result demonstrates a magnetic control of the binding energy of the fluctuating particle-hole pairs in the Slater-Mott crossover regime [Nat. Commun. 10, 5301 (2019)]. |
Tuesday, March 16, 2021 9:36AM - 9:48AM Live |
E55.00007: Structural modulated inteplay between charge and spin in the pseudospin-1/2 state within Slater-Mott crossover regime Junyi Yang, Lin Hao, Han Zhang, Shashi Pandey, Dongliang Gong, Jian Liu Systems described by the Hubbard Hamiltonian sitting on bipartite lattices are important for capturing the correlated physics of various emergent phenomena, including high temperature superconductivity in the cuprates. The emergence of pseudospin-1/2 state on a square lattice in the layered perovskite iridate has provided an alternative system akin to the parent compound of cuprates with a similar antiferromagnetic Mott insulating state. Moreover, the much stronger spin-orbit coupling and relatively weaker electron correlation of the pseudospin-1/2 electrons have resulted in novel electronic and magnetic behaviors that are absent or could not be captured in the cuprate family. This includes the strong collective spin-charge fluctuations in an intermediate regime of the Hubbard Hamiltonian, which is also referred as Slater-Mott crossover regime. In virtue of epitaxial strain tuning of iridate thin films, we show that the pseudospin-1/2 electronic state is highly susceptible to structural degree of freedom, enabling an effective tuning of the electron correlation within the crossover regime. Our combined results on transport properties and synchrotron-based x-ray scattering reveal the electronic and magnetic responses to the correlation modulation in both the 2D and 3D regimes. |
Tuesday, March 16, 2021 9:48AM - 10:00AM Live |
E55.00008: Reviving dead layer magnetism by interface tailoring with strong spin-orbit materials David Howe, Mohammad Saghayezhian, Zhen Wang, Zeeshan Ali, Prahald Siwakoti, Yimei Zhu, E Ward Plummer, Jiandi Zhang Ferromagnetic (FM) onset in doped manganates is usually accompanied by a metal-insulator transition and colossal magneto-resistance. In the extremely thin film limit, materials tend to lose their functionality and become non-magnetic and insulating, i.e. “dead”. We have discovered that below the dead-layer thickness, through interfacial coupling, a strong re-entrant FM-insulating phase with very large magneto-resistance can appear. We created heterostructures of La.7Ca.3MnO3 (LCMO)-X-LCMO on SrTiO3 (001) where X is the buffer layer (SrTiO3, CaRuO3 and SrRuO3). The buffer materials were selected based on their structure, electronic properties and magnetism to identify how the interfacial coupling might affect the magnetic and electronic properties in LCMO. We found that SrRuO3, an FM-metal with strong spin-orbit coupling, has the most drastic effect on the magnetic onset temperature (~200K TC increase) and net magnetization, even with the addition of only a single unit cell of SrRuO3. We also find these films to remain insulating despite this magnetic resuscitation, pointing toward a novel magnetic order beyond the usual double-exchange. We will discuss the underlying physics using atomic-scale microscopy and spectroscopy. |
Tuesday, March 16, 2021 10:00AM - 10:12AM Live |
E55.00009: Origin of orbital polarization in LaCoO3+LaTiO3: DFT+U and DMFT study Alex Lee, Sohrab Ismail-Beigi Orbital polarization, i.e., the degree of broken orbital degeneracy, can play a crucial role in the electronic and magnetic properties of transition metal oxides. Recently, we observed strong orbital polarization of Co2+ in LaCoO3+LaTiO3 (LCO+LTO) superlattices, but the underlying origin of this orbital polarization was not fully understood. The orbital polarization of the Co2+ cation is particularly interesting since it has multiple spin states, and the dominant t2g or eg character is determined by the spin state. We systematically study the origin of the orbital polarization of Co2+ by considering the various structural phases of (LCO)1+(LTO)1 superlattices and the La2CoTiO6 double perovskite, using density functional theory (DFT)+U and dynamical mean-field theory (DMFT) calculations. While we find that structural symmetry reduction is the primary origin of the orbital polarization, the Coulomb U causes spontaneously broken electronic symmetry and large polarizations in some of the DFT+U calculations. We show that this symmetry breaking is artificial as fluctuations between multiple configurations (i.e., Slater determinants) as captured by DMFT restore the symmetry: caution is required when only using DFT+U to compute such observables. |
Tuesday, March 16, 2021 10:12AM - 10:48AM Live |
E55.00010: Cooperative evolution of polar distortion and nonpolar rotation of oxygen octahedra in oxide heterostructures Invited Speaker: Jaekwang Lee The polarity discontinuity across LaAlO 3 /SrTiO 3 (LAO/STO) heterostructure induces |
Tuesday, March 16, 2021 10:48AM - 11:00AM Live |
E55.00011: Octahedra rotations coupling in perovskite vanadate heterostructures Stefano Gariglio, Hugo Meley, Duncan T.L. Alexander, Jean-Marc Triscone Octahedral rotations patterns in transition metal perovskites affect their physical properties due to the strong coupling between the lattice and electronic degrees of freedom. Across an interface in an epitaxial heterostructure, the corner sharing of the oxygen octahedra has been shown to modify the natural rotation pattern of the layer; the extent and structural details of the affected region are currently at the focus of several studies. In this work, we investigate by scanning transmission electron microscopy (STEM) the interface between two orthorhombic structures which display in their bulk part a different orientation of their tilt patterns. The heterostructure consists of a LaVO3 film epitaxially grown onto a (110)o DyScO3 substrate. STEM imaging reveals the existence of an atomically sharp chemical interface and a 10 unit cell thick structural transition layer |
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