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Synthesis and Study on the Spin-Charge Interaction in Topological Semimetal/Ferromagnet Heterostructures
Senior Investigator: Luqiao Liu, Assistant Professor, Department of Electrical Engineering and Computer Science

The main focus of the proposed work will be to (1) develop the synthesis process which can seamlessly integrate topological semimetal thin film with ferromagnet electrode, and (2) study the mutual interaction between charge and spin at the topological semimetal/ferromagnet interface. For the first part of the proposed efforts, various growth techniques such as sputtering and molecular beam epitaxy will be employed and the obtained film stacks will be characterized. For the second part, nanoscale devices will be fabricated for the magneto-electrical transport measurement. It is expected that the successful implementation of the proposed topological semimetal/ferromagnet heterostructure could be used to reduce the energy consumption (by more than a factor of 100x) of magnetic random access memories (MRAM), which has been extensively studied as a promising beyond CMOS technology for replacing existing electronic memory and logic devices. In the meantime, through the proposed study, deeper understanding will be gained on the spin and charge transport properties at the topological material/ferromagnet interface, which can lay a solid physical ground for the future development of electronic systems such as topological quantum computer, where the mutual interaction between topological ordering and magnetic ordering plays important roles.

IRG 1 designs adaptive materials whose morphology and functionality are actively controlled by chemical or optical fueling. Inspired by biological systems, these materials enable technologies like energy-efficient optical coatings, soft robotics, and advanced manufacturing through innovations in nanocrystal and biopolymer networks.

The goal of this IRG is to gain quantitative insight into, and predictive capability of, the molecular mechanisms that govern the unique structure and property combinations of complex biological hydrogels. This fundamental knowledge is used to guide the synthesis, fabrication, and evaluation of next generation materials with potentially wide engineering implications, such as the design of self-healing filtration systems for water and food purification, new antimicrobial coatings for implants, or cartilage substitutes with high durability and lubrication capacity. This IRG is divided into three interconnected thrusts. The thrust efforts are designed to investigate the molecular chemistry and structure-property relationships of repeat domains, reversible crosslinking and glycosylation, and use the resulting knowledge to synthesize bio-enabled hydrogels that strategically contain all three elements. Thrust 1 uses the well-defined repetitive domains from the nuclear pore complex hydrogel to study their role for the filtration properties of biological hydrogels. Thrust 2 uses tools from chemical engineering to identify how specific dynamics and chemistry of reversible crosslinks relate to key bulk material properties such as viscoelasticity, self-healing and durability. Building on this knowledge, the IRG is adapting prioritized types of crosslinking to generate hydrogels with controlled behavior. Thrust 3 seeks to determine the biological function of polymer-associated glycan chains in regulating the biomechanical and filtration properties, as well as cellular interactions, of hydrogels.

This Materials Research Science and Engineering Center (MRSEC) is a collaboration between Stanford University, the University of California at Davis and IBM Almaden Research Center. The MRSEC focuses on the interface science of polymeric and surface-active molecules that will enable advances in information technologies. The Center also provides seed funding for new opportunities in materials research. The Center supports regional, national and international outreach efforts that impact education at all levels, including summer research experiences for undergraduates, international exchanges of students and faculty, development of instructional materials for high school students and materials science education of the general public through a regional museum. The MRSEC also supports shared experimental facilities that are accessible to center participants and to outside users, and broad industrial outreach efforts.

Research in this Center, which has been named the Center on Polymer Interfaces and Macromolecular Assemblies, is organized into two interdisciplinary research groups. One group investigates the structure, dynamics and properties of polymers confined to surfaces and interfaces with the goal of understanding lubrication and adhesion processes at the molecular level. A second group emphasizes the development of thin film polymeric membranes as biomolecular materials for sensor and diagnostic applications.

Thin Film Chromium Oxide Perovskites
Senior Investigator: Riccardo Comin, Assistant Professor, Department of Physics
 

Transition metal oxides (TMOs) have found use in various technologies. There has been mounting interest to harness the spin-charge interplay of TMOs and engineer new data storage devices relying on all-electrical (current or field) writing operations.

The relationship between magnetic order and electronic transport in TM-based compounds suggest that ferromagnets (FM) are typically metals, while antiferromagnets (AFM) are insulators. Compounds as such these are on the verge between different magnetic and electronic ground states, an ideal platform to design materials that are highly tunable by external parameters such as doping or magnetic field. Further, in these materials, the realization of room-temperature metallic conduction with robust AFM order could pave the way to new oxide-based magnetic access memories for fast magnetization switching using spin-transfer torque.

We propose to explore focuses on a family of transition metal oxides with a rich phenomenology: chromium-based oxide perovskites (chromites). We propose to study the combined charge and spin response in Cr-based perovskite thin films in the multidimensional domain spanned by strain, dimensionality (thickness), and doping (chemical substitution or oxygen removal). The novelty of our work lies in the exploration of a relatively new class of materials, and the impact of the proposed work is in the synergistic feedback between synthesis and characterization of the charge and spin response to reveal the driving forces behind the complex phenomenology of chromites.

The IRG is aimed at exploring and exploiting ferroelectric (FE) polarization as a state variable that allows realization of polarization-controlled electronic, transport, and other functional properties of oxide, organic, and hybrid FE-based structures. This involves ferroelectrically induced resistive switching phenomena and the associated memristive behavior, FE modulation of electronic confinement at the hybrid FE/semiconductor and organic interfaces, as well as development of novel functional systems based on newly synthesized organic ferroelectrics where molecular interactions are responsible for macroscopic dipole ordering. These scientifically rich problems comprise the involvement of multiple degrees of freedom, the critical role of interfaces, and the interplay between physical and chemical properties at the nanoscale. They require comprehensive fundamental understanding and hold a lot of promise for technological innovations, including new paradigms for data storage and conceptually novel photovoltaic applications.

Thin Film Chromium Oxide Perovskites

Transition metal oxides (TMOs) have found use in various technologies. There has been mounting interest to harness the spin-charge interplay of TMOs and engineer new data storage devices relying on all-electrical (current or field) writing operations.

The relationship between magnetic order and electronic transport in TM-based compounds suggest that ferromagnets (FM) are typically metals, while antiferromagnets (AFM) are insulators. Compounds as such these are on the verge between different magnetic and electronic ground states, an ideal platform to design materials that are highly tunable by external parameters such as doping or magnetic field. Further, in these materials, the realization of room-temperature metallic conduction with robust AFM order could pave the way to new oxide-based magnetic access memories for fast magnetization switching using spin-transfer torque.

We propose to explore focuses on a family of transition metal oxides with a rich phenomenology: chromium-based oxide perovskites (chromites). We propose to study the combined charge and spin response in Cr-based perovskite thin films in the multidimensional domain spanned by strain, dimensionality (thickness), and doping (chemical substitution or oxygen removal). The novelty of our work lies in the exploration of a relatively new class of materials, and the impact of the proposed work is in the synergistic feedback between synthesis and characterization of the charge and spin response to reveal the driving forces behind the complex phenomenology of chromites.

The grand challenge of this IRG is to understand how to manipulate light on the nanometer length scale and, thereby, implement new amplified sensing and information encoding strategies. Particles and arrays can amplify and confine light through excitation of their localized surface plasmon resonances (LSPRs). The materials of interest include chemically synthesized noble metal nanoparticles, nanofabricated arrays of noble metal nanoparticles and nanoholes, and surface functionalization chemistry for these nanomaterials. It is anticipated that the new materials produced through rational nanoparticle synthesis/fabrication—and in particular through understanding of their growth mechanism(s) and properties—will have a transformative impact on applications such as ultrasensitive chemical and biosensing, nanoscale optical spectroscopy and microscopy, and information processing.

The UMass MRSEC mission 

 Materials research at UMass Amherst has a rich history of fundamental discovery centered in polymers and extending across the landscape of colloidal materials, surface science, and nanoscale structures. NSF support for the UMass MRSEC has been instrumental in landmark findings in polymer crystallization, block copolymer assembly for high density addressable media, ultrathin free-standing nanoscale structures, and state-of-the-art advances in polymer adhesion and self-healing. Our materials research mission merges with vibrant programs designed to educate students towards rewarding careers in science and technology. This is manifest in teaching and mentoring, where UMass Amherst is a national leader in graduate education in polymers and soft materials chemistry, physics, and engineering. Our educational mission extends to all ages and grade levels, thanks to a rich diversity of Center-supported programs designed for undergraduates, teachers, and grade school children alike. Today the UMass MRSEC seeks to define the future of polymer materials science and engineering, with research teams engaged in innovative multidisciplinary projects that push fundamental boundaries and create new technologies.