Plant secondary metabolite-dependent plant-soil feedbacks can improve crop yield in the field.

Plant secondary metabolites that are released into the rhizosphere alter biotic and abiotic soil properties, which in turn affect the performance of other plants. How this type of plant-soil feedback affects agricultural productivity and food quality in the field in the context of crop rotations is unknown. Here, we assessed the performance, yield and food quality of three winter wheat varieties growing in field plots whose soils had been conditioned by either wild type or benzoxazinoid-deficient bx1 maize mutant plants. Following maize cultivation, we detected benzoxazinoid-dependent chemical and microbial fingerprints in the soil. The benzoxazinoid fingerprint was still visible during wheat growth, but the microbial fingerprint was no longer detected. Wheat emergence, tillering, growth, and biomass increased in wild type conditioned soils compared to bx1 mutant conditioned soils. Weed cover was similar between soil conditioning treatments, but insect herbivore abundance decreased in benzoxazinoid-conditioned soils. Wheat yield was increased by over 4% without a reduction in grain quality in benzoxazinoid-conditioned soils. This improvement was directly associated with increased germination and tillering. Taken together, our experiments provide evidence that soil conditioning by plant secondary metabolite producing plants can increase yield via plant-soil feedbacks under agronomically realistic conditions. If this phenomenon holds true across different soils and environments, optimizing root exudation chemistry could be a powerful, genetically tractable strategy to enhance crop yields without additional inputs

Thermal and electrostatic tuning of surface phonon-polaritons in LaAlO₃/SrTiO₃ heterostructures

Phonon polaritons are promising for infrared applications due to a strong light-matter coupling and subwavelength energy confinement they offer. Yet, the spectral narrowness of the phonon bands and difficulty to tune the phonon polariton properties hinder further progress in this field. SrTiO3 – a prototype perovskite oxide - has recently attracted attention due to two prominent far-infrared phonon polaritons bands, albeit without any tuning reported so far. Here we show, using cryogenic infrared near-field microscopy, that long-propagating surface phonon polaritons are present both in bare SrTiO3 and in LaAlO3/SrTiO3 heterostructures hosting a two-dimensional electron gas. The presence of the two-dimensional electron gas increases dramatically the thermal variation of the upper limit of the surface phonon polariton band due to temperature dependent polaronic screening of the surface charge carriers. Furthermore, we demonstrate a tunability of the upper surface phonon polariton frequency in LaAlO3/SrTiO3 via electrostatic gating. Our results suggest that oxide interfaces are a new platform bridging unconventional electronics and long-wavelength nanophotonics.</p

Competition between Carrier Injection and Structural Distortions in Electron‐Doped Perovskite Nickelate Thin Films

The discovery of superconductivity in doped infinite‐layer nickelate thin films has brought increased attention to the behavior of the doped perovskite phase. Despite this interest, the majority of existing studies pertain to hole‐doped perovskite rare‐earth nickelate thin films, while most electron‐doping studies have been performed on bulk materials so far. To tackle this imbalance, a detailed study that addresses doping of NdNiO$_{3}$ thin films using A‐site substitution is presented, using Pb as a dopant and taking advantage of its valence‐skipping nature. Through a combination of complementary techniques including X‐ray diffraction, transport measurements, X‐ray absorption spectroscopy, electron energy‐loss spectroscopy and scanning transmission electron microscopy, the valence of Pb in the Nd$_{1−x}$Pb$_{x}$NiO$_{3}$ structure is confirmed to be 4+, and the behavior of the doped thin films is found to be controlled by a competition between carrier injection and structural distortions, which respectively reduce and increase the metal‐to‐insulator transition temperature. This work provides a systematic study of electron doping in NdNiO$_{3}$, demonstrating that A‐site substitution with Pb is an appropriate method for such doping in perovskite rare‐earth nickelate systems

Competition between Carrier Injection and Structural Distortions in Electron-Doped Perovskite Nickelate Thin Films

The discovery of superconductivity in doped infinite-layer nickelate thin films has brought increased attention to the behavior of the doped perovskite phase. Despite this interest, the majority of existing studies pertain to hole-doped perovskite rare-earth nickelate thin films, while most electron-doping studies have been performed on bulk materials so far. To tackle this imbalance, a detailed study that addresses doping of NdNiO thin films using A-site substitution is presented, using Pb as a dopant and taking advantage of its valence-skipping nature. Through a combination of complementary techniques including X-ray diffraction, transport measurements, X-ray absorption spectroscopy, electron energy-loss spectroscopy and scanning transmission electron microscopy, the valence of Pb in the NdPbNiO structure is confirmed to be 4+, and the behavior of the doped thin films is found to be controlled by a competition between carrier injection and structural distortions, which respectively reduce and increase the metal-to-insulator transition temperature. This work provides a systematic study of electron doping in NdNiO, demonstrating that A-site substitution with Pb is an appropriate method for such doping in perovskite rare-earth nickelate systems

Electronic transport in sub-micrometric channels at the LaAlO3_{3}/SrTiO3_{3} interface

Nanoscale channels realized at the conducting interface between LaAlO$_{3}$ and SrTiO$_{3}$ provide a perfect playground to explore the effect of dimensionality on the electronic properties of complex oxides. Here we compare the electric transport properties of devices realized using the AFM-writing technique and conventional photo-lithography. We find that the lateral size of the conducting paths has a strong effect on their transport behavior at low temperature. We observe a crossover from metallic to insulating regime occurring at about 50 K for channels narrower than 100 nm. The insulating upturn can be suppressed by the application of a positive backgate. We compare the behavior of nanometric constrictions in lithographically patterned channels with the result of model calculations and we conclude that the experimental observations are compatible with the physics of a quantum point contact.Comment: 9 pages, 6 figure

Oxygen Control in Infinite-Layer Cuprate Heterostructures

Le mécanisme régissant la supraconductivité à haute température critique, observée dans des composés à base de cuivre et d’oxygène (cuprates), n’est à ce jour pas encore entièrement élucidé. Dans cette thèse sont étudiés des systèmes dits « infinite-layer » avec la formule chimique ACuO2 (A=Sr, Ca). Ces composés sont constitués de plans de CuO2 intercalés entre deux plans de cations A. L’objectif de l’étude est double : d’un côté, le but est d’insérer, dans les plans du cation A, des atomes d’oxygène qui, de par leur valence et leur position apical au cuivre, dopent la phase isolante. Ce dopage a pour effet de promouvoir un état métallique et potentiellement supraconducteur. À cet effet les conditions de synthèse de ces matériaux sont adaptées. Le second aspect concerne le control de la position de l’atome d’oxygène apical au cuivre à l’interface de bicouches SrTiO3/CaCuO2 afin d’en modifier l’état supraconducteur. Dans cette intention un champ électrique est utilisé afin de déplacer l’oxygène apical

Structural and electronic properties of SrCuO2+ δthin films

The layered structure of superconducting cuprates is considered to be a key ingredient to achieve high superconducting transition temperatures. In this work, we investigate the possibility of doping the SrCuO2 infinite-layer compound by inserting additional oxygen into its structure. We observe that the infinite-layer SrCuO2 structure is epitaxially stabilized in thin films grown by pulsed laser deposition in pure O2. Increasing the oxidizing power by introducing ozone during the growth leads to a different phase with an elongated c axis. Scanning transmission electron microscopy analysis suggests that the films with an elongated c axis are composed of SrCuO2.5 blocks separated by SrCuO2 layers arranged to match the substrate spacing. X-ray absorption spectroscopy measurements show that this SrCuO2+δ phase is associated with a more isotropic Cu orbital configuration and hole doping. This hole doping leads to a dramatic reduction in the resistivity of the films, with a magnitude that depends on the precise oxygen content in the structure.This work was supported by the Swiss National Science Foundation—Division II (Grant No. 200020_179155) and by the European Research Council under the European Union Seventh Framework Programme, Grant No. FP7/2007–2013 and ERC Grant Agreement No. 319286 (Q-MAC). M.G. and G.D.L. acknowledge support by the Swiss National Science Foundation under Grant No. PP00P2_17056

Competition between carrier injection and structural distortions in electron-doped perovskite nickelate thin films

AbstractData repository for the paper published in Advanced Electronic Materials