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 M55: Nickelates and ManganitesFocus Live
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Sponsoring Units: DMP Chair: Yuri Suzuki, Stanford Univ |
Wednesday, March 17, 2021 11:30AM - 12:06PM Live |
M55.00001: Thickness-dependent perovskite octahedral distortions at heterointerfaces Invited Speaker: Jennifer Fowlie The plethora of exotic physics found in transition metal oxides is no accident, it directly reflects the particularly fascinating chemistry of the d-orbitals. The d wavefunctions are highly directional and electronically very localized, leading to a strong coupling between the lattice, electronic and spin degrees of freedom. This means, therefore, that fine details of the crystal structure can have important consequences for the material properties. One famous example of this remarkable sensitivity is the family of perovskite rare earth nickelates where the temperature of their electronic and magnetic phase transitions are greatly modified by small changes of the Ni-O-Ni bond angle. The sublattice of corner connected O6 octahedra is therefore essential in driving the physics of these materials and many other perovskites like them. |
Wednesday, March 17, 2021 12:06PM - 12:18PM Live |
M55.00002: Mapping electronic phase coexistence in nickelate superlattices by STEM-EELS Bernat Mundet, Duncan T.L. Alexander, Claribel Dominguez Ordonez, Jennifer Fowlie, Marta Gibert, Jean-Marc Triscone To study the electronic couplings, and their characteristic length-scales, that are established at the coherent interfaces of epitaxial heterostructures, novel characterization techniques capable of mapping electronic phase coexistence at the atomic-scale level are required. Here, we show that scanning transmission electron microscopy in combination with electron energy-loss spectroscopy (STEM-EELS) can be used to map electronic phase coexistence in rare-earth nickelate materials. |
Wednesday, March 17, 2021 12:18PM - 12:30PM Live |
M55.00003: Fundamental difference in the electronic reconstruction of infinite-layer vs. perovskite neodymium nickelate films on SrTiO3(001) Benjamin Geisler, Rossitza Pentcheva Motivated by the recent observation of superconductivity in the infinite-layer nickelate NdNiO2 on SrTiO3(001) by Li et al. [1], we explore the effect of interface polarity on the electronic properties of NdNiOn/SrTiO3(001) (n = 2,3) by performing first-principles calculations including a Coulomb repulsion term [2]. For infinite-layer nickelate films (n = 2), electronic reconstruction drives the emergence of a 2DEG at the interface involving a strong occupation of the Ti 3d states. This effect is more pronounced than in LaAlO3/SrTiO3(001) and accompanied by a substantial reconstruction of the Fermi surface: a depletion of the self-doping Nd 5d states and an enhanced Ni eg orbital polarization, reflecting a single hole in the 3dx2−y2 states, i.e., cupratelike behavior. In contrast, no 2DEG forms for perovskite films (n = 3). We show that the topotactic reaction from the perovskite to the infinite-layer phase is confined to the nickelate film, whereas the SrTiO3 substrate remains intact. Finally, we highlight differences between infinite-layer nickelate and cuprate films on SrTiO3(001). |
Wednesday, March 17, 2021 12:30PM - 12:42PM Live |
M55.00004: The role of the interface in La0.67Sr0.33MnO3/YBa2Cu3O7-δ heterostructures probed by polarized neutron reflectometry Jacob Wisser, Alexander Grutter, Patrick Quarterman, Purnima Parvathy Balakrishnan, Brian James Kirby, Yuri Suzuki The interplay of ferromagnetism and superconductivity at interfaces can lead to proximity effects, spin valve behavior, and spin triplet pairing, with the interface playing an important role. To further explore this role, we have studied magnetotransport in YBa2Cu3O7-δ (YBCO)/La0.67Sr0.33MnO3 (LSMO) heterostructures fabricated via pulsed laser deposition on (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT) (001) substrates. We compare the electronic and magnetic properties of LSMO/YBCO/LSMO trilayers with YBCO/LSMO and LSMO/YBCO bilayers to separate contributions from each interface from spin valve behavior in the magnetoresistance of the samples. All samples show magnetoresistance peaks at low field, indicating the peak is due to stray fields from the LSMO layers rather than spin valve behavior. Polarized neutron reflectometry highlights the importance of the interface. All samples show a 2-3 nm thick disordered layer at each LSMO/YBCO interface, which may prevent the LSMO layers from coupling through the YBCO layer in the trilayer heterostructures and inhibit large magnetoresistance due to spin valve behavior. |
Wednesday, March 17, 2021 12:42PM - 12:54PM Live |
M55.00005: Tuning the Charge Distribution via Strain Engineering in Manganite-Cuprate Heterostructures Yu-Mi Wu, Gideok Kim, Georg Cristiani, Gennady Logvenov, Y. Eren Suyolcu, Bernhard Keimer, Peter A. van Aken The exploration of strain engineering in complex oxide heterostructures has unveiled the microscopic origins of macroscopic properties and led to the precise control of the local physical behavior in materials at the nanoscale. Here, we reveal the local charge distribution in manganese oxides by means of high spatial and energy resolution scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). Our direct quantification of charge arrangement gives insight into how the strain locally alters the physical properties of La0.5Sr0.5MnO3 - La2CuO4 heterostructures. We find that the magnitude of the charge redistribution can be controlled via the epitaxial strain, which further influences the macroscopic electronic and magnetic structures differently from the strain affects reported on single-phase films. Our findings offer a new way of controlling local phases in manganites and novel design of relevant electronic and spintronic devices. |
Wednesday, March 17, 2021 12:54PM - 1:06PM Live |
M55.00006: Spontaneous Phase Segregation of Sr2NiO3 and SrNi2O3 during SrNiO3 Heteroepitaxy Le Wang, Zhenzhong Yang, Xinmao Yin, Hua Zhou, Scott Chambers, Yingge Du The rich phase diagrams of complex oxide nickelates (RNiO3) are of critical importance for both materials physics and oxide electronics. Hole doping in RNiO3 has been studied as an effective strategy for tuning their functional properties, including enhanced electrocatalytic properties found in La1-xSrxNiO3 and superconducting behavior observed in reduced Nd1-xSrxNiO2. However, the synthesis of stochiometric R1-xSrxNiO3 thin films over a range of x has proven challenging, presumably because of the instability of Ni oxidation states greater than +3. Moreover, little is known about the structures and properties of the end member SrNiO3. Here, we show that spontaneous phase segregation occurs while depositing SrNiO3 thin films on perovskite oxide substrates by molecular beam epitaxy. Two co-existing oxygen-deficient Ruddlesden-Popper phases, Sr2NiO3 and SrNi2O3, are formed to balance the stoichiometry and stabilize the energetically preferred Ni2+ cation. Our study sheds light on an unusual oxide thin-film nucleation process driven by the tendency of transition metal cations to form their most stable valence (i.e., Ni2+ in this case). The resulting metastable reduced Ruddlesden-Popper structures offer a testbed for further studying the emerging phenomena in nickel-based oxides. |
Wednesday, March 17, 2021 1:06PM - 1:18PM Live |
M55.00007: Probing the electronic ground states of thin film Ruddlesden-Popper (Rn+1NinO3n+1) nickelates Grace Pan, Qi Song, Dan Ferenc Segedin, Spencer Doyle, Harrison LaBollita, Hanjong Paik, Charles Brooks, Antia Sanchez Botana, Julia Mundy The recent discovery of superconductivity in a hole-doped infinite layer nickelate has spurred the reexamination of how nickelate physics may be amenable to stabilizing new superconducting phases [1]. The nickelate identified is isostructural to the superconducting cuprates and lies squarely in the superconducting regime of the simple phase diagram by Zhang [2] but disentangling the electronic from the structural contributions presents a key challenge. We have stabilized, for the first time, the Ruddlesden-Popper nickelates (Ndn+1NinO3n+1) in thin film form, including non-bulk stable orders up to n = 6. We will discuss how tuning of the Ruddlesden-Popper order alters the electronic ground states of the system including the nickel 3d occupancy and effects on the canonical metal-to-insulator transition. |
Wednesday, March 17, 2021 1:18PM - 1:54PM Live |
M55.00008: Tuning the electronic and thermoelectric response of oxide superlattices by confinement, strain and interface polarity Invited Speaker: Rossitza Pentcheva Transition metal oxides are prospective candidates for energy conversion applications e.g. as thermoelectrics owing to their chemical and thermal stability and in particular to their complex correlated nature. Nanostructuring and reduced dimensionality can lead to further performance enhancement. By combining DFT+U calculations and Boltzmann transport theory we explore the implications of interface polarity, confinement and strain on the thermoelectric properties of perovskite superlattices. Taking as an example LaNiO3/SrTiO3(001), we demonstrate that compatible n- and p-type materials can be realized by selective choice of the layer stacking at polar interfaces [1]. Furthermore, a strongly enhanced thermoelectric response is obtained in nonpolar LaNiO3/LaAlO3(001) superlattices due to the confinement-driven metal-to-insulator transition [2]. This concept is further extended to (SrXO3)1/(SrTiO3)n(001) SL with X = V, Cr, and Mn [3]. Last but not least, the thermoelectric properties of topologically nontrivial Chern insulating phases are discussed [4]. |
Wednesday, March 17, 2021 1:54PM - 2:06PM Live |
M55.00009: Charge Engineering of RNiO3-based Mott Transistors with a Ferroelectric Gate Yifei Hao, Xuegang Chen, Le Zhang, Xia Hong We present a comprehensive study of ferroelectric-gated Mott transistors based on high-quality epitaxial heterostructures composed of a ferroelectric Pb(Zr,Ti)O3 (PZT) gate and a correlated oxide RNiO3 (R = La, Nd, Sm) channel. For single-layer nickelate channels, including Sm0.5Nd0.5NiO3, NdNiO3 (NNO), and LaNiO3 (LNO), the resistance switching ratio ΔR/Ron increases exponentially with decreasing channel thickness until it approaches the electrical dead layer thickness, with the maximum ΔR/Ron~200% observed in 1 nm LNO channel. Inserting a La1-xSrxMnO3 (LSMO) buffer layer can lead to over two orders of magnitude increase in ΔR/Ron for devices with the same channel thickness, which is attributed to a tailored density profile due to the interfacial charge transfer. Our studies highlight the intricate interplay of charge itineracy and carrier density in determining the performance limit of ferroelectric gated mott-transistor. |
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