Quantum materials with kagome lattice – comprised of corner-sharing triangles forming a hexagon in the crystal structure - have been studied as the potential playgrounds for exploring the interplay among parameters such as geometry, topology, electronic correlations, magnetic, and charge density orders. Niobium halides, Nb3X8 (X = Cl, Br, I), which are predicted to be two-dimensional magnets, have recently received attention due to their breathing kagome geometry. In this talk, I will discuss the electronic structure of Nb3X8 system revealed by angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. ARPES results depict the presence of multiple flat and weakly dispersing bands. These bands are well reproduced by the theoretical calculations, which show that they have Nb d character indicating their origin from the Nb atoms forming the breathing kagome plane. These van der Waals materials can be easily thinned down via mechanical exfoliation to the ultrathin limit and such ultrathin samples are stable as shown from the time-dependent Raman spectroscopy measurements at room temperature. These results demonstrate that Nb3X8 system is an excellent material platform for studying breathing kagome induced flat band physics and its connection with magnetism. I will also discuss our recent results on topological quantum materials using ultrafast spectroscopy. 

About the speaker:

Dr. Neupane received his Ph.D. in Physics from Boston College, Boston, MA in 2010. He spent four years (2011-2014) as a postdoctoral research associate at Princeton University, Princeton, NJ and one year (2015-2016) as a Director’s Fellow at Los Alamos National Laboratory, Los Alamos, NM. He joined UCF in 2016 as an Assistant Professor and reached Associate Professor in 2020. He is the recipient of the Director’s Fellow at Los Alamos National Laboratory (2015), NSF Career Award (2019), UCF Luminary Award (2019), and UCF Research Incentive Award (2020). Neupane has been recognized as a highly cited researcher from 2019 to 2023 by analytics company Clarivate, based on data from Web of Science. His research focuses on the electronic and spin properties of new quantum materials. He utilizes various spectroscopic techniques to reveal the interesting electronic and spin properties as well as the momentum resolved dynamical properties of the bulk and symmetry-protected properties of the surface of these quantum materials.

Abstract: 

The manipulation of matter on the nanoscale can enable useful technologies with interesting underlying physics. Nano-patterned graphene facilitates standing-wave plasmonic behavior that can be used for surface-sensitive chemical detection. Owing to its versatility, this two-dimensional material can also be utilized in area-selective atomic layer deposition (AS-ALD) processes to make robust resistive memory cells. In turn, more technologically scalable routes of AS-ALD can be employed to make self-limiting electronic tunneling junctions. These diverse, but related, topics will be presented, and will hopefully be instructive to those interested in plasmonics, electronics, and materials science.

Glasses doped with rare-earth (RE) ions as possible opto-electronic materials have gained considerable interest. Heavy metal oxide glasses have been shown to improve the efficiency of RE ion’s fluorescence properties. The optical absorption and fluorescence properties of RE ions can be optimized by altering the chemical environment around the RE ions. Chemical environment of RE ions can be varied through the glass composition or by introducing metal/semiconducting nanoparticles (NPs) into the host glass matrix. In the present talk, I will discuss the effect of CdSe NPs on the fluorescence properties of praseodymium (Pr3+) ions. These NPs are grown in bismuth-boro tellurite glasses through controlled annealing for different durations. Our results show that the presence of CdSe NPs of certain specific size led to improved fluorescence efficiency of Pr3+ ions. 

About the speaker:

Dr. Mallur obtained her Ph.D. in Solid State Physics from the Indian Institute of Science, Bangalore (1996), India.  She did her post-doctoral work in University of Illinois at Urbana-Champaign. Currently she is a full professor at the department of physics, Western Illinois University. Her current research interests are in the synthesis of glasses doped with rare-earth ions and study their electronic and optical properties using optical absorption and fluorescence experiments. In addition, she also investigates the effect of nanoparticles on the optical properties of rare-earth ions in glasses. 

Transition metal dichalcogenide (TMD) based moiré materials have been shown to host various correlated electronic phenomena including Mott insulating states and fractional filling charge orders, quantum spin Hall effects, and (fractional) quantum anomalous Hall effects. To describe the low-energy states of long-wavelength moiré superlattice, we introduced the concept of moiré quantum chemistry, and developed transfer learning based large-scale first principle methods. In twisted bilayer TMD, we proposed the Mott ferroelectricity, kinetic magnetism and pseudogap metal from spin polarons. The pseudogap metal phase emerges at small doping below half filling and an intermediate range of fields, which exhibits a single-particle gap and a doping-dependent magnetization plateau.

I will also discuss the fractional quantum anomalous Hall effect in twisted homobilayer and its competing states. This series of works reveal the rich physics of semiconductor moiré superlattices as manifested in a variety of correlated and topological states. 

About the speaker:

Dr. Yang Zhang is an assistant professor in physics at the University of Tennessee, Knoxville, and visiting professor at Max Planck Institute Dresden. He received his BE degree from Tsinghua University and Ph.D. in Physics from Max Planck Institute Dresden, then he worked as a postdoc at MIT. His research interest lies in understanding the correlated/topological states, quantum transport, and light-matter interaction in quantum materials. Yang has received several awards, including the Tschirnhaus Medal from the Leibniz Association, and the Otto-Hahn Medal of the Max Planck Society.

Abstract: The breaking of time-reversal symmetry in topological insulators leads to novel quantum states of matter. One prominent example at the two-dimensional limit is the Chern insulator, which hosts dissipationless chiral edge states at sample boundaries. These chiral edge modes are perfect one-dimensional conductors whose chirality is defined by the material magnetization and in which backscattering is topologically forbidden. Recently, van der Waals topological magnet MnBi2Te4 emerged as a new solid-state platform for studies of the interplay between magnetism and topology. In this talk, I will present an overview of our progress toward controlling topological phase transitions and chiral edge modes in MnBi2Te4 as well as discovering new quantum states in this material family. First, I will establish how topological properties are intimately intertwined with magnetic states. I will then demonstrate electrical control of the number of chiral edge states and the discovery of chiral edge modes along crystalline steps between regions of different thicknesses and how these modes can be harnessed for the engineering of simple topological circuits. Finally, I will discuss the engineering of the superconducting state in topological insulators and demonstrate Pauli paramagnetic limit violation in atomically thin flakes of a topological superconductor candidate.

Bio: Dmitry Ovchinnikov earned his Ph.D. from the Institute of Electrical and Micro Engineering at École Polytechnique Fédérale de Lausanne (EPFL), Switzerland in 2017. During his Ph.D., he conducted experiments on two-dimensional semiconductors and developed techniques to modulate disorder in low-dimensional systems. His thesis earned him the EPFL EDMI PhD thesis distinction award and the Gilbert Hausmann PhD thesis award. He received an early postdoc Swiss National Science Foundation (SNSF) mobility fellowship to research nanoscale van der Waals magnetic devices at the University of Washington with Prof. Xiaodong Xu. Currently, Dmitry is an Assistant Professor at the Department of Physics and Astronomy at the University of Kansas. His work involves exploring the fundamental physics and applications of topological magnets, superconductors, and correlated states in low-dimensional quantum materials.

“Phases and dynamics of dipolar gases and universality of ferromagnetic superfluids” 

This presentation consists of two separate parts. In the first, we will discuss the static properties and the dynamics of dipolar Dysprosium Bose-Einstein condensates subjected to a fastly rotating external magnetic field. The underlying phase diagram with respect to the atom number and relative interaction strengths for various field orientations is mapped out. Transitions  from a superfluid to a supersolid and then to arrays of dipolar droplets characterized by a non-vanishing global phase coherence will be elucidated. Following quenches, across the aforementioned phase transitions, we observe the dynamical nucleation of supersolids or droplet lattices. Three-body losses lead to self-evaporation of the ensuing structures, while the rotating magnetic field enables, for fixed values of the relative interactions, an enhancement of the droplet lifetimes. The second part will be devoted to  address universality in the non equilibrium dynamics of a two-dimensional ferromagnetic spinor gas subjected to modulations of the quadratic Zeeman coefficient. For short timescales we observe the spontaneous nucleation of topological defects (spin-vortices) which annihilate through their interaction giving rise to magnetic domains deeper in the evolution where the gas enters the universal coarsening regime. This is characterized by the spatiotemporal scaling of the spin correlation functions and the structure factor allowing to measure corresponding scaling exponents which depend on the symmetry of the order parameter and belong to distinct universality classes. These results represent a paradigmatic example of categorizing far-from-equilibrium dynamics in quantum many-body systems and reveal the interplay of topological defects for the emergent universality class.

Abstract: Self-assembling peptides have emerged as a cutting-edge class of materials that can be engineered to form one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) nanostructures, with diverse potential applications in bioimaging, tissue engineering, controlled drug delivery, and as catalysts and sensitive elements in biosensors. These peptide compounds are highly versatile molecular building blocks, attributable to their rich chemical diversity and inherent affinity for biological interfacing. The functionalization of these nanomaterials with nanoparticles of transition metals, conjugated polymers, and photoluminescent compounds has expanded their application range within nanotechnology. Moreover, organized systems of peptides have shown significant promise in asymmetric catalysis, particularly in aldol reactions, offering a novel route for synthesizing optically active compounds. This seminar primarily focuses on designing peptide-based materials for asymmetric catalysis and constructing biomimetic systems, emphasizing applications in biosensor devices.

Wendel Andrade Alves is a Full Professor at the Federal University of ABC, Brazil, and a Research Fellow of the Brazilian National Council for Scientific and Technological Development (CNPq), Level 1B. He has a Ph.D. in Chemistry from the University of São Paulo, Brazil, where he also completed a Post-Doctoral fellowship in Physical Chemistry at the Laboratory of Electroactive Materials. His research interests involve the supramolecular assembly of natural and synthetic polymers, the self-assembly of peptides, and biosensor development.
 

Understanding and manipulating quantum superposition are important quests in quantum materials research. One exciting direction emerging in the field is to use the geometry of quantum states – the so-called quantum geometry – as a means of characterizing quantum superposition. This approach has successfully characterized various electric and magnetic properties of materials, which are not easily captured by semiclassical approaches. In this seminar, I will first introduce a general theory of the quantum geometry of resonant optical electric-dipole responses in materials. I will discuss the new insights from this quantum-geometric paradigm, guiding us to discover and investigate new optical phenomena. In the second part, I will talk about an intriguing optical response going beyond electric-dipole transitions: a surprising Kerr effect in certain antiferromagnets that are non-quantized but owe their existence to axion electrodynamics. This response has recently been observed in experiments and used for the optical control of antiferromagnets. Finally, I will give an outlook for future directions.

Weyl semimetals are among the materials proposed to have significant potential in informational technologies and to harbor the necessary elements for quantum computing. They host Weyl nodes at specific points in their Brillouin zone, a pair of relativistic fermions with different chirality, Weyl fermions. The nontrivial momentum-space topology due to the Weyl nodes leads to various fascinating phenomena, such as the chiral anomaly, chiral magnetic effect, anomalous magnetoresistance and Hall effect, large nonsaturating thermoelectric power and ultrafast photocurrents just to name a few. The essential ingredients for the realization of the Weyl semimetal are the absence of inversion symmetry and/or time-reversal symmetry. The RAlX (where R=Rare Earth and X=Ge, Si) family, where both symmetries are broken, has been recently identified as a large class of Weyl semimetal based on systematic first-principles band structure calculations and APRES measurements. In this respect, I will present details and importance of crystal growth of non-centrosymmetric CeAlGe single crystals, their physical properties, anomalous magnetotransport, and discuss the future implications of our findings and the tunability of RAlGe and RAlSi families.  

Cryo–electron microscopy (cryo-EM) has been proven a powerful tool visualizing biological specimen. Method developments in single-particle analysis (SPA) and in situ tomography have enabled more structures to be imaged and determined to attenable resolutions. Sample-to-structure pipeline is essential for an imaging Core in improving the productivity and efficiency in structural determination. As the Director, I am leading the MU Electron Microscopy Core (EMC) in collaboration with MU research laboratories from Physics, Material Science, Computer Science, Biochemistry etc. to develop and implement such a unique pipeline housed in NextGen. Cryo-EM will continue its remarkable growth in technology advancement in the next decades. MU provides great centralized microscopy resource at EMC for scientists from all fields to advance their career and research. We welcome collaborations. 

Abstract:

The conventional electronic system has been developed upon Si-based thin-films because of their cost-effectiveness and mature process. However, there are fundamental limitations in using conventional systems towards future electronics such as wearable devices, biomedical devices, and edge computing devices. One of these most prevalent limitations is that current thin-film electronic systems have been developed on rigid wafers, which causes serious physical constrains because of the thick nature of the materials on the rigid wafers. Thus, an alternative approach has been required to secure mechanically low stiffness of materials and devices.

In this talk, I will discuss about our recent effort to tackle the aforementioned challenge by developing 3D and 2D freestanding nanomembranes. First of all, we have conceived an approach to obtain freestanding single crystalline materials through 2D materials assisted layer-transfer (2DLT). While developing it, we found out that crystallographic information can penetrate through graphene as long as substrates have polarity because of graphene’s information transparency. Also, the slippery nature of graphene enables spontaneous relaxation, which substantially reduces dislocation density in heteroepitaxy. Second, we have developed mechanics to produce 2D materials by playing interfacial toughness contrast. As this approach allows producing various 2D materials at large-scale, various applications can be demonstrated at practical level. Also, we realized that geometrical confinement helps kinetic control of 2D materials, which secures crystallinity, layer-controllability, and heterostructures. As the 3D and 2D freestanding membranes are a new type of building blocks, various opportunities are expected by providing a new platform where physical couplings and practical applications are conceived.

Bio:

Sang-Hoon Bae is an Assistant Professor in Washington University in St. Louis. He was a postdoctoral research associate at Massachusetts Institute of Technology (MIT) working with Professor Jeehwan Kim before joining Washington University. He earned a doctorate in materials science and engineering from University of California, Los Angeles (UCLA) under the supervision of Professor Yang Yang in 2017. He earned bachelor's and master's degrees in materials science and engineering from Sungkyunkwan University (SKKU), Korea, under the supervision of Professor Jong-Hyun Ahn in 2013. He worked at IBM T. J. Watson Research Center (2014) and Samsung Display (2010) as a research intern. He has published more than 70 papers in notable journals including Science, Nature, PNAS, Nature Materials, Nature Nanotechnology, Nature Photonics, and Nature Electronics with over 8000 citations. His h-index is 41 as of March 2023. 

Abstract:

Semiconductor nanocrystals are promising candidates for generating chemical feedstocks through photocatalysis in which photoexcited charge carriers are used to perform charge-transfer reactions. However, the fate of photoexcited charges once they reach the surface, i.e., whether they recombine or are extracted to initiate useful redox reactions, is highly sensitive to the structure of the surface. Our research group is investigating how oxygen vacancies, a common type of surface defect in metal oxide semiconductors, control their photocatalytic activity. Using single-molecule, super-resolution fluorescence microscopy, we image both spatial and temporal variations in the photocatalytic activity of individual semiconductor nanocrystals such as bismuth oxybromide and tungsten oxide. To understand the chemical origins of these variations in activity we apply a combination of ensemble structural characterization, electronic-structure calculations, and the quantitative spatial correlation of multiple fluorogenic probes. Our results show that both photoexcitation and chemical modifications to the surface of semiconductor nanocrystals can be used to tune the concentration and distribution of oxygen vacancies in these materials, which has a significant impact on their resulting catalytic activity. In one system, bismuth oxybromide, a high concentration of oxygen vacancies decreases activity, while in tungsten oxide, it increases activity. Thus, to achieve high performance for a desired catalytic transformation, our results demonstrate it is necessary to tune the concentration and type of defects for the specific photocatalyst. Ultimately, photocatalysts containing a stable, intermediate concentration of oxygen vacancies may prove to be optimal for balancing the activity of both reductive and oxidative transformations in a system that generates chemical fuels from sunlight.

Bio: Bryce Sadtler graduated from Purdue University in 2002 with a B.S. degree in Chemistry. He conducted his graduate studies at the University of California, Berkeley under the guidance of Paul Alivisatos and received a Ph.D. in Physical Chemistry in 2009. He was then a Beckman Institute Postdoctoral Fellow at the California Institute of Technology, where he worked with Nathan Lewis and Harry Atwater. Bryce joined the Department of Chemistry at Washington University in St. Louis in 2014. His research interests include solid-state chemistry and light–matter interactions in nanoscale materials for applications in solar energy conversion and catalysis. He has received an NSF Career award (2018), an ACS PRF Doctoral New Investigator Award (2017), and was named an Emerging Investigator by the Journal of Materials Chemistry (2017). Bryce was promoted to an Associate Professor at Washington University in July 2022.

Abstract:

Surfaces and interfaces, also referred to as phase boundaries, play an important role in material performance for the application in nanodevices. When the surface of a material comes in contact with another phase, interaction occurs at the interface between the phases which initiates the alteration of properties at the phase boundaries. Therefore, the analysis of the surface properties plays a crucial role in understanding the fundamental insights of crystal growth, reaction kinetics and basis for engineering the nanoparticles as well as interpreting the quantum physics and resolving the theoretical prejudice.

Two-dimensional (2D) materials have drawn enormous research interests due to their intriguing physical properties along with potential applications in the next generation nano-devices. The growth of some 2D materials, such as, Xenes, requires supporting substates which have strong impact on the formation of these materials and their properties. Hence, investigating the surface properties of these types of 2D materials has become quite essential. Recently invented 2D boron (B) sheet which is known as borophene, is considered as a promising material; consists of B atoms arranged in triangular lattice with hollow hexagons. The synthesis of 2D B sheet is still challenging and strongly dependent on the supporting substrates and their crystalline faces, and other factors including temperature, deposition rate etc. during preparation. It is evident from surface analysis by Low energy electron diffraction (LEED), Scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) in ultra-high vacuum (UHV) condition that completely different types of B structures are formed on transition metal substrates with different crystalline faces. The dependency of B growth on substrates creates the opportunities to realize the best substrate for the growth of 2D B sheet which can be employed in future applications.