Understanding and engineering two-dimensional electron gases in complex oxides

The next generation of electronic devices faces the challenge of adequately containing and controlling extremely high charge densities within structures of nanometer dimensions. Atomic-scale transistors must be thin and be able to control extremely high charge densities (>10e13/cm^2). Silicon devices typically have two-dimensional electron gas (2DEG) densities around 10e12/cm^2. Nitride-based devices can sustain densities an order of magnitude higher. The "complex oxides" have recently emerged as an attractive materials system to support these developments. The demonstration of a 2DEG at the SrTiO3/LaAlO3 interface has triggered an avalanche of research, including the unprecedentedly high density of 3x10e14/cm^2 at SrTiO3/GdTiO3 and SrTiO3/SmTiO3 interfaces. Metal-insulator (Mott) transitions that are inherent to some of these complex oxides could offer even greater prospects for enhanced functionality or novel device concepts.The materials and heterostructures that have been explored to date are clearly only a small subset of the vast number of materials combinations that could lead to interesting phenomena. In this work we use first-principles methods to build greater understanding of the interface phenomena, so that searches can be better informed and more focused. We also develop a set of criteria that the materials and their heterostructures should satisfy to develop a high-performance 2DEG-based device. We focus in particular on the band alignment, calculating it for a variety of different potential materials. Next, we study GdTiO3/SrTiO3/GdTiO3 heterostructures in depth, where each interface contributes excess electrons into the SrTiO3. We calculate the 2DEG formation for a superlattice containing six layers of SrTiO3, and compare with angle-resolved photoemission spectroscopy results. Together, the experimental and theoretical results conclusively show that the 2DEG results from the interface itself, and does not originate from a secondary source such as oxygen vacancies. These heterostructures also exhibit a metal-to-insulator transition as the SrTiO3 layer thickness decreases, which could possibly be used as a "Mott field effect transistor" - the system is very close to a metal-to-insulator transition, and modulating a small fraction of the electron density would lead to switching between the metallic and insulating phases. The mechanism behind this transition is unraveled, and we construct a bulk model of the transition based on the surprising observation that SrTiO3 itself can become a Mott insulator when doped with an extremely high density of electrons.Building on our study of the SrTiO3/GdTiO3 interfaces, we investigate the electronic structure of GdTiO3 in detail - our calculated band gap differs markedly from past experimental values, but is consistent with recent photoluminescence measurements. We find that the presence of small hole polarons leads to a feature in the optical absorption spectrum which was previously interpreted to be the band gap. Since small hole polarons are present in all the rare-earth titanates, not only GdTiO3, the values of the band gaps (also based on optical absorption measurements) across the series will likely have to be revised. Lastly, to understand the formation of small hole polarons in the rare-earth titanates, we study point defects and impurities in GdTiO3. We also investigate how defects may impact the behavior of GdTiO3 in electronic devices

Structural investigation of the bilayer iridate Sr_3Ir_2O_7

A complete structural solution of the bilayer iridate compound Sr_3Ir_2O_7 presently remains outstanding. Previously reported structures for this compound vary and all fail to explain weak structural violations observed in neutron scattering measurements as well as the presence of a net ferromagnetic moment in the basal plane. In this paper, we present single crystal neutron diffraction and rotational anisotropy second harmonic generation measurements unveiling a lower, monoclinic symmetry inherent to Sr_3Ir_2O_7. Combined with density functional theory, our measurements identify the correct structural space group as No. 15 (C2/c) and provide clarity regarding the local symmetry of Ir^(4+) cations within this spin-orbit Mott material

Structural investigation of the bilayer iridate Sr_3Ir_2O_7

A complete structural solution of the bilayer iridate compound Sr_3Ir_2O_7 presently remains outstanding. Previously reported structures for this compound vary and all fail to explain weak structural violations observed in neutron scattering measurements as well as the presence of a net ferromagnetic moment in the basal plane. In this paper, we present single crystal neutron diffraction and rotational anisotropy second harmonic generation measurements unveiling a lower, monoclinic symmetry inherent to Sr_3Ir_2O_7. Combined with density functional theory, our measurements identify the correct structural space group as No. 15 (C2/c) and provide clarity regarding the local symmetry of Ir^(4+) cations within this spin-orbit Mott material

Towards a European Health Research and Innovation Cloud (HRIC)

The European Union (EU) initiative on the Digital Transformation of Health and Care (Digicare) aims to provide the conditions necessary for building a secure, flexible, and decentralized digital health infrastructure. Creating a European Health Research and Innovation Cloud (HRIC) within this environment should enable data sharing and analysis for health research across the EU, in compliance with data protection legislation while preserving the full trust of the participants. Such a HRIC should learn from and build on existing data infrastructures, integrate best practices, and focus on the concrete needs of the community in terms of technologies, governance, management, regulation, and ethics requirements. Here, we describe the vision and expected benefits of digital data sharing in health research activities and present a roadmap that fosters the opportunities while answering the challenges of implementing a HRIC. For this, we put forward five specific recommendations and action points to ensure that a European HRIC: i) is built on established standards and guidelines, providing cloud technologies through an open and decentralized infrastructure; ii) is developed and certified to the highest standards of interoperability and data security that can be trusted by all stakeholders; iii) is supported by a robust ethical and legal framework that is compliant with the EU General Data Protection Regulation (GDPR); iv) establishes a proper environment for the training of new generations of data and medical scientists; and v) stimulates research and innovation in transnational collaborations through public and private initiatives and partnerships funded by the EU through Horizon 2020 and Horizon Europe

Understanding and engineering two-dimensional electron gases in complex oxides

The next generation of electronic devices faces the challenge of adequately containing and controlling extremely high charge densities within structures of nanometer dimensions. Atomic-scale transistors must be thin and be able to control extremely high charge densities (>10e13/cm 2). Silicon devicestypically have two-dimensional electron gas (2DEG) densities around 10e12/cm 2.Nitride-based devices can sustain densities an order of magnitude higher. The "complex oxides" have recently emerged as an attractive materials system to support these developments. The demonstration of a 2DEG at the SrTiO 3/LaAlO3 interface has triggered an avalanche of research, including the unprecedentedly high density of 3x10e14/cm 2 at SrTiO3/GdTiO3and SrTiO3/SmTiO3 interfaces. Metal-insulator (Mott) transitions that are inherent to some of these complex oxides could offer even greater prospects for enhanced functionality or novel device concepts. The materials and heterostructures that have been explored to date are clearly only a small subset of the vast number of materials combinations that could lead to interesting phenomena. In this work we use first-principles methods to build greater understanding of the interface phenomena, so that searches can be better informed and more focused. We also develop a set of criteria that the materials and their heterostructures should satisfy to develop a high-performance 2DEG-based device. We focus in particular on the band alignment, calculating it for a variety of different potential materials. Next, we study GdTiO3/SrTiO3/GdTiO3 heterostructures in depth, where each interface contributes excess electrons into the SrTiO3. We calculate the 2DEG formation for a superlattice containing six layers of SrTiO3, and compare with angle-resolved photoemission spectroscopy results. Together, the experimental and theoretical results conclusively show that the 2DEG results from the interface itself, and does not originate from a secondary source such as oxygen vacancies. These heterostructures also exhibit a metal-to-insulator transition as the SrTiO 3 layer thickness decreases, which could possibly be used as a "Mott field effect transistor" — the system is very close to a metal-to-insulator transition, and modulating a small fraction of the electron density would lead to switching between the metallic and insulating phases. The mechanism behind this transition is unraveled, and we construct a bulk model of the transition based on the surprising observation that SrTiO3 itself can become a Mott insulator when doped with an extremely high density of electrons. Building on our study of the SrTiO3/GdTiO3 interfaces, we investigate the electronic structure of GdTiO3 in detail - our calculated band gap differs markedly from past experimental values, but is consistent with recent photoluminescence measurements. We find that the presence of small hole polarons leads to a feature in the optical absorption spectrum which was previously interpreted to be the band gap. Since small hole polarons are present in all the rare-earth titanates, not only GdTiO3, the values of the band gaps (also based on optical absorption measurements) across the series will likely have to be revised. Lastly, to understand the formation of small hole polarons in the rare-earth titanates, we study point defects and impurities in GdTiO3. We also investigate how defects may impact the behavior of GdTiO3 in electronic devices

Towards a European health research and innovation cloud (HRIC)

The European Union (EU) initiative on the Digital Transformation of Health and Care (Digicare) aims to provide the conditions necessary for building a secure, flexible, and decentralized digital health infrastructure. Creating a European Health Research and Innovation Cloud (HRIC) within this environment should enable data sharing and analysis for health research across the EU, in compliance with data protection legislation while preserving the full trust of the participants. Such a HRIC should learn from and build on existing data infrastructures, integrate best practices, and focus on the concrete needs of the community in terms of technologies, governance, management, regulation, and ethics requirements. Here, we describe the vision and expected benefits of digital data sharing in health research activities and present a roadmap that fosters the opportunities while answering the challenges of implementing a HRIC. For this, we put forward five specific recommendations and action points to ensure that a European HRIC: i) is built on established standards and guidelines, providing cloud technologies through an open and decentralized infrastructure; ii) is developed and certified to the highest standards of interoperability and data security that can be trusted by all stakeholders; iii) is supported by a robust ethical and legal framework that is compliant with the EU General Data Protection Regulation (GDPR); iv) establishes a proper environment for the training of new generations of data and medical scientists; and v) stimulates research and innovation in transnational collaborations through public and private initiatives and partnerships funded by the EU through Horizon 2020 and Horizon Europe

The coming decade of digital brain research - A vision for neuroscience at the intersection of technology and computing

<p>Brain research has in recent years indisputably entered a new epoch, driven by substantial methodological advances and digitally enabled data integration and modeling at multiple scales – from molecules to the whole system. Major advances are emerging at the intersection of neuroscience with technology and computing. This new science of the brain integrates high-quality basic research, systematic data integration across multiple scales, a new culture of large-scale collaboration and translation into applications. A systematic approach, as pioneered in Europe's Human Brain Project (HBP), will be essential in meeting the pressing medical and technological challenges of the coming decade. The aims of this paper are</p><ul><li>To develop a concept for the coming decade of digital brain research</li><li>To discuss it with the research community at large, with the aim of identifying points of convergence and common goals</li><li>To provide a scientific framework for current and future development of EBRAINS</li><li>To inform and engage stakeholders, funding organizations and research institutions regarding future digital brain research</li><li>To identify and address key ethical and societal issues</li></ul><p>While we do not claim that there is a 'one size fits all' approach to addressing these aspects, we are convinced that discussions around the theme of digital brain research will help drive progress in the broader field of neuroscience.</p><p><strong>As the final version 5 has now been published, comments on this manuscript are now closed. We thank everyone who made a valuable contribution to this paper.</strong></p><p>This manuscript has been developed in a participatory process. The work has been initiated by the Science and Infrastructure Board of the Human Brain Project (HBP), and the entire research community was invited to contribute to shaping the vision by submitting comments. </p><p>All submitted comments were considered and discussed. The final decision on whether edits or additions was made to each version of the manuscript based on an individual comment was made by the Science and Infrastructure Board (SIB) of the Human Brain Project (HBP).</p><p><strong>Supporters of the paper</strong>: Pietro Avanzini, Marc Beyer, Maria Del Vecchio, Jitka Annen, Maurizio Mattia, Steven Laureys, Rosanne Edelenbosch, Rafael Yuste, Jean-Pierre Changeux, Linda Richards, Hye Weon Jessica Kim, Chrysoula Samara, Luis Miguel González de la Garza, Nikoleta Petalidou, Vasudha Kulkarni, Cesar David Rincon, Isabella O'Shea, Munira Tamim Electricwala, Bernd Carsten Stahl, Bahar Hazal Yalcinkaya, Meysam Hashemi, Carola Sales Carbonell, Marcel Carrère, Anthony Randal McIntosh, Hiba Sheheitli, Abolfazl Ziaeemehr, Martin Breyton, Giovanna Ramos Queda, Anirudh NIhalani Vattikonda, Gyorgy Buzsaki, George Ogoh, William Knight, Torbjørn V Ness, Michiel van der Vlag, Marcello Massimini, Thomas Nowontny, Alex Upton, Yaseen Jakhura, Ahmet Nihat Simsek, Michael Hopkins, Addolorata Marasco, Shamim Patel, Jakub Fil, Diego Molinari, Susana Bueno, Lia Domide, Cosimo Lupo, Mu-ming Poo, George Paxinos, Huifang Wang.</p&gt