Search

IRG4 seeks to understand and control the organization of particle mixtures to generate photonic and electronic architectures in which non-additive functions are imparted by the collective properties of the array. Co-assemblies will incorporate multiple, distinct particle populations that vary in composition and consequently in their response to various directed self-assembly approaches (Figure, top/middle). Learning how to achieve desired assembly outcomes despite these differences, and to find ways to take advantage of them for increased control, will set the stage for a new era of nanomaterial-enabled device applications well beyond those proposed here. Three general classes of multicomponent assemblies will be investigated, incorporating new types of functional particles and spanning a wide range of organizational ordering schemes (Figure, bottom): (1) well-ordered arrays with single-particle positioning relative to underlying electrical contacts for fundamental studies of bioinspired synchronization in electronic oscillator networks; (2) arrays with intermediate order that will collectively define the spatial refractive index profile to manipulate light in new ways; (3) disordered assemblies of scattering particles to advance understanding of ‘random’ photonics, with a focus on lasing and nonlinear wave mixing.

IRG-1 brings together a diverse team of solid-state chemists, condensed matter physicists, and electrical engineers to create materials systems with topological electronic phases and to probe and understand their novel properties using a variety of experimental and theoretical techniques. It proposes a broad program that includes the study of topological quantum states in novel insulators, semiconductors, metals, superconductors and magnetic materials.

This IRG builds on our previous successes in the study of topological phases in Bi-based semiconductors to further develop the new class of topological crystalline insulators and metals with strongly spin-split electronic states to explore helical bulk electronic systems. To realize topological superconducting phases, we harness atomic scale engineering and self-assembly to realize new nanoscale systems that are expected to harbor topological excitations that are Majorana fermions.  Looking beyond Majorana fermions, we use our state-of-the art molecular beam epitaxy (MBE) growth of extremely high mobility two-dimensional electron systems and combine these systems together in bilayers and with superconductors to search for Majorana-like excitations (parafermions) that are predicted to be excitations of an interacting topological state. Magnetic systems provide a unique setting to explore topological phases and their excitations in condensed matter systems and will be another focus of our program; one particularly interesting system we plan to examine is made up of chains of coupled magnetic moments in which there are emergent low energy fermionic excitations. Frustrated and Kagome lattices of spins provide their own opportunities to create spin systems that have interesting low energy topological excitations.

Co-Leaders
R. J. Cava, co-leader (Chemistry)
N. P. Ong, co-leader (Physics)

Senior Investigators
B. A. Bernevig (Physics)
F. D. M. Haldane (Physics)
L. Pfeiffer (Elec. Engin.)
M. Shayegan (Elec. Engin.)
Donna D. N. Sheng (Cal. State Northridge)
Leslie Schoop (Chemistry)
A. Yazdani (Physics)  

Collaborators
T. Valla (Brookhaven Nat. Lab.)
G. Gu (Brookhaven Nat. Lab.)
V. Bayot (Catholic Univ. Louvain, Belgium)
M. Lilly (Sandia National Labs)
Qi-kun Xue (Tsinghua, Beijing)
Yayu Wang (Tsinghua, Beijing)

IRG-1 publications
IRG-1 highlights

Metal nanoparticles (e.g., Au, Ag, Cu, Al) are essential components in the toolbox of plasmonic nanostructures. Bottom-up chemical synthesis offers the potential for scaling up the materials production, as well as tailoring optical properties by fine tuning size, shape and surface beyond the conventional photolithography limit. We aim to develop rational synthesis strategies for producing nanoparticles with desired morphologies (nanowires, nanocubes, nano square cuboids), and for building up a knowledge base of shape-properties relationships. Such nanoparticles can be used as the building blocks in many areas such as plasmonic circuits, surface enhanced Raman scattering (SERS), bioimaging and even cancer therapy.

This IRG investigates mechanical properties in soft matter and interfaces that are both a scientific challenge and an important technological problem. Understanding the mechanical behavior of materials requires insight into phenomena at different length scales. This IRG has established the importance of mechanics in describing soft materials and interfaces with more traditional hard materials.

Magnetically and Optically Driven Topological Semimetals

In the past decade, there has been remarkable progress in our understanding of topological states of matter. A quantum state is topological if its ground state wave function bears a distinctive character that can be specified by a topological invariant—a discrete quantity that remains unchanged upon adiabatic deformations of the system. Since the 1980s, quantum Hall systems have been recognized to be topological, but it was long believed that such topological states are rather exceptional in nature and only exist in quantum liquids under extreme conditions (requiring high magnetic fields and low temperatures). However, after the discovery of topological insulators (TIs), it has come to be widely recognized that topological states of matter can actually be widespread. In this sense, TIs have established a new paradigm about topological materials and opened up an interdisciplinary field at the crossroad between physics,quantum chemistry and material science.

The goal of this research is to discover two new types of TSMs in magnetic and photo-driven systems respectively, and explore their novel properties. First, magnetic TSMs consist of itinerant electrons that form the Dirac/Weyl point in k-space and localized moment that generates magnetism. The exchange coupling between the two is expected to catalyze a plethora of novel correlated phenomena, including an anomalous Hall effect induced by Berry curvature, an axion electromagnetic response, tunable Weyl point creation/annihilation, and metal-insulator transitions. Despite intensive searches, magnetic TSMs have not been experimentally found. The PIs will combine theoretical and experimental efforts to search for magnetic TSMs in correlated electron systems.

Second, the PIs propose a new topological phase of matter in photon-electron hybrid states, which they term the Floquet topological semimetal. Recent experiments lead by the PI Gedik has demonstrated that Bloch states in solids can be “dressed” by intense laser light, forming “Floquet-Bloch states” that are completely coherent and behave like real bands. When these states form topologically robust band crossings in energy-momentum space, the photo-excited system is expected to become a Floquet topological semimetal. The PI Fu will theoretically determine the photon polarization and frequency required for this new phase, while Checkelsky will provide the necessary materials platform and Gedik use well-established time resolved photoemission techniques to uncover these Floquet TSMs.

I. Magnetic Topological Semimetals
An important class of TSMs, known as Weyl semimetals, is proposed to materialize in magnetic topological insulators, where time-reversal symmetry is spontaneously broken. Fu’s group will use first-principles calculations to identify such magnetically driven TSMs in candidate materials and predict their emergent phenomena. Checkelsky’s group will synthesize samples and characterize their transport and magnetic properties, which will then be studied by Gedik’s group using angle-resolved photoemission spectroscopy (ARPES) to directly observe the Dirac/Weyl point in the bulk and the topological surface states with Fermi arc. Gedik’s group will further perform optical and magneto-optical measurements to thoroughly characterize the electronic structure. In addition to its scientific value, the discovery of TSMs may enable new spintronic device application, where electrical properties can be efficiently tuned by magnetization.

II. Floquet Topological Semimetals
Besides the static optical and photoemission measurements probing the equilibrium, Gedik will also study the dynamics of the material in response to photoexcitation by light. Gedik has recently showed that by shining light with energy below the bulk band gap of a topological insulator, hybrid photon-electron states can be created. These states are called Floquet-Bloch states, which are the Bloch states “dressed” by the intense laser light. Surface electrons coherently can emit and absorb multiple laser photons giving rise to replicas of the original dispersion separated by integer multiples of photon energy. These new states are completely coherent and behave like real bands for practical purposes. When these bands cross they can hybridize and open up band gaps along certain directions. Considering the fact that material properties are largely determined by electronic dispersion, this ability to manipulate the electronic band structure with light is a novel way to engineer novel quantum phases of matter. There have been a number of proposals for inducing phase transitions using Floquet methods, such as inducing a Floquet topological insulator from a trivial insulator.

The Materials Research Science and Engineering Center (MRSEC) at Michigan State University focuses on sensing materials for control and diagnostics. The Center also provides seed funding for new opportunities in sensor materials. The Center supports education outreach efforts that include research experiences for undergraduates and outreach to the pre-college level through hands-on workshops for junior high school science teachers. 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 MRSEC is organized into two interdisciplinary research groups. One group emphasizes optical probes of processes critical to engine diagnostics and sensing. A second group explores various transduction methods for transforming chemical and physical information into electrical signals. Participants in the Center currently include 21 senior investigators, 3 postdoctoral associates, 11 graduate students, 8 undergraduates, and one administrative support personnel. Professor Brage Golding directs the MRSEC.

The Materials Research Science and Engineering Center (MRSEC) at the University of Maryland supports interactive research in two interdisciplinary groups focusing on oxides, thin films, and novel surface spectroscopic probes. One of the research groups emphasizes fundamental materials issues in ferroelectric thin film heterostructures , related device problems of technological relevance, and fundamental materials physics of perovskite materials that exhibit unusually large ("colossal") magneto- resistance. The second group investigates the structure of surfaces on length scales from nanometers to microns, with the goal of developing a predictive understanding of surface morphology. The work may ultimately find practical application in micro-electronics, thin film growth, lubrication, catalysis, and other areas. A common theme for both groups is the development, optimization and utilization of novel surface sensitive tools to measure structural, magnetic, and electrical properties at microscopic length scales. The MRSEC supports the development, operation and maintenance of shared experimental facilities for materials research. It provides seed funding for exploratory research and fosters research participation by undergraduates. The Center is associated with an educational outreach program designed to enlighten pre-college and undergraduate students about science and the role of the center's research program in the modern world. The MRSEC also supports enhanced collaboration with industry, shared experimental facilities that also support research not directly funded by the MRSEC, and seed funding for exploratory research. The Center currently supports about 15 senior investigators, 7 postdoctoral research associates, 1 technician or other professional, 12 graduate students, and 8 undergraduates. The MRSEC is directed by Professor Ellen D. Williams. %%% The Materials Research Science and Engineering Center (MRSEC) at the University of Maryland supports interactive research in two interdisciplinary groups focusing on oxides, thin films, and novel surface spectroscopic probes. One of the research groups emphasizes fundamental materials issues in ferroelectric thin film heterostructures , related device problems of technological relevance, and fundamental materials physics of perovskite materials that exhibit unusually large ("colossal") magneto- resistance. The second group investigates the structure of surfaces on length scales from nanometers to microns, with the goal of developing a predictive understanding of surface morphology. The work may ultimately find practical application in micro-electronics, thin film growth, lubrication, catalysis, and other areas. A common theme for both groups is the development, optimization and utilization of novel surface sensitive tools to measure structural, magnetic, and electrical properties at microscopic length scales. The MRSEC supports the development, operation and maintenance of shared experimental facilities for materials research. It provides seed funding for exploratory research and fosters research participation by undergraduates. The Center is associated with an educational outreach program designed to enlighten pre-college and undergraduate students about science and the role of the center's research program in the modern world. The MRSEC also supports enhanced collaboration with industry, shared experimental facilities that also support research not directly funded by the MRSEC, and seed funding for exploratory research. The Center currently supports about 15 senior investigators, 7 postdoctoral research associates, 1 technician or other professional, 12 graduate students, and 8 undergraduates. The MRSEC is directed by Professor Ellen D. Williams.

The focus of IRG-2, Sustainable Nanocrystal Materials, is the design, synthesis, processing, and thin film properties of environmentally benign nanocrystal-based electronic and optoelectronic materials. The field is currently constrained by the use of toxic (e.g., Pb, Cd) and/or scarce (e.g., In, Te) elements, with serious environmental, health, and economic concerns. IRG-2 will overcome these barriers by discovering and developing nanocrystal-based electronic thin films made from nontoxic, abundant and sustainable materials using scalable, low-temperature processes. The IRG's research will pursue three closely linked, vertically integrated thrusts: (i) nanocrystal synthesis and characterization; (ii) quantum dot films and devices; and (iii) microcrystalline films and devices. This research aims to reinvent the scope of active materials for NC-based electronics and optoelectronics, which will ultimately enable energy efficient emissive or photovoltaic devices with sustainable materials choices.

Seeds 7 is working to design nano-structured materials for wide bandwidth operation that can be used to greatly enhance nonlinear interactions, including nonlinear frequency conversion (NFC) processes: frequency mixing between two or more photons.

Principal Investigators
Alejandro Rodriguez (Electrical Engineering)
Loren Pfeiffer (Electrical Engineering)
Claire Gmachl (Electrical Engineering)

* This seed is inactive. (Seed start/end date: April 1, 2016 - October 31, 2018)

Bottlebrush Hydrogels as Tunable Tissue Engineering Scaffolds
Senior Investigator: Robert Macfarlane, Assistant Professor, Department of Materials Science and Engineering

Tissue engineering (TE) is a promising method to grow artificial tissues for biological and biomedical applications, typically implemented using a porous, flexible, and biocompatible scaffold for cells so that, upon growth and proliferation, they ultimately form a continuous three-dimensional biomaterial1,2. However, living cells and tissues are complex constructs, and synthesizing scaffolds that properly interact with them remains a challenge; scaffolds need to simultaneously be (1) biocompatible, (2) mechanically matched to the native tissue, (3) porous enough to allow for nutrient flow and tissue development, and (4) capable of presenting molecular signals that promote cell growth and viability. Therefore, while hydrogels are a promising tool for medicine and biology, several key limitations in these biomedical technologies can only be addressed via advances in the field of materials science.

Here, we will develop methods to synthesize new BBP architectures, crosslink them into gels, and characterize how different design variables affect the resulting gel physical, chemical, and mechanical properties. Our lab is uniquely suited to study these materials, as we possess the requisite polymer
synthesis and characterization capabilities necessary, and have proven expertise in manipulating soft material structure at the nanoscale via controlled polymer synthetic strategies10. Additional support from other member of CMSE IRG II will aid in our characterization capabilities.