2023
Dec
6
2023
“Molecular beam epitaxy of functional complex 4d and 5d transition metal oxides.”
ABSTRACT: Thin film synthesis methods of complex transition metal oxides had their wake-up call when superconductivity was discovered in cuprates in 1986. Advancements in sputter deposition, pulsed laser deposition, and most notably in molecular beam epitaxy followed and culminated in customized layering growth methods that allowed for artificially designed complex transition metal oxides. Besides, rich magnetic ordering phenomena in manganates, ferrites, cobaltates, and nickelates triggered a burst into thin film synthesis methods of complex transition metal oxides. Yet, such materials of interest are all centered around 3d complex transition metal oxides. Regarding thin film synthesis methods like pulsed laser deposition, complex transition metal oxides based on 4d or 5d systems are accessible, yet at the cost of crystalline quality. On the other hand, the synthesis of 4d or 5d complex transition metal oxides from bare metals is not feasible owing to the typically low vapor pressures of these elements. We overcame this problem by developing a molecular beam epitaxy system that is empowered exclusively by electron guns. These electron guns are controlled by electron impact emission spectrometry (EIES), where individual elemental fluxes are tuned to meet desired stoichiometries in real time. For 4d and 5d complex transition metal oxides a true rate control system is indispensable as the oxidation process is commonly accompanied by the formation of volatile oxides. For example, for the synthesis of superconducting Sr2RuO4 thin films with ozone as an oxidizing agent, the Ru flux is 13–14% higher than stoichiometrically required. The excess ruthenium will be converted to RuO3 and RuO4 during the synthesis process and eventually condense at the vacuum chamber walls. Furthermore, we discuss the synthesis of Nd2−xCexPdO4 thin films by molecular beam epitaxy. Finally, we will stroll through the synthesis procedures of complex osmates. In there, extremely high temperatures coincide with the formation of extremely volatile species, e.g., OsO3 and OsO4. Nonetheless, this materials synthesis exploration approach is an enabler for hitherto unknown and unexplored materials with intriguing physical properties.
Darrin Communications Center (DCC) 330 4:00 pm
Nov
29
2023
"The Invisible Halo of Gas Around Galaxies"
Abstract: When we think of a galaxy, we often imagine a spinning disk of stars and gas surrounding a glowing center. But galaxies are more than meets the eye, and the disks we see are just a small part of the whole. We now know galaxies to be surrounded by huge halos of gas that provide the material from which stars are formed. In this lecture, we will explore the scope of these nearly invisible halos, describe how we can detect them, and look at computer simulations that help reveal their lesser known properties and their influences, such as magnetic fields!
Darrin Communications Center (DCC) 330 4:00 pm
Nov
15
2023
The Robert Resnick Lecture: "Dark Matter in the Universe"
The nature of the dark matter in the Universe is among the longest and most important outstanding problems in all of modern physics. The ordinary atoms that make up the known universe, from our bodies and the air we breathe to the planets and stars, constitute only 5% of all matter and energy in the cosmos. The remaining 95% is made up of a recipe of 25% dark matter and 70% dark energy, both nonluminous components whose nature remains a mystery. I’ll begin by discussing the evidence that dark matter is the bulk of the mass in the Universe, and then turn to the hunt to understand its nature. Leading candidates are fundamental particles including Weakly Interacting Massive Particles (WIMPs), axions, sterile neutrinos, light dark matter, as well as primordial black holes. I will discuss multiple experimental searches: at CERN in Geneva; in underground laboratories; with space telescopes; with gravitational wave detectors; and even with DNA. I’ll tell you about our novel idea of Dark Stars, early stars made primarily of hydrogen but powered by dark matter heating, and the possibility that the James Webb Space Telescope has already discovered them. At the end of the talk, I'll turn to dark energy and its effect on the future of the Universe.
Darrin Communications Center (DCC) 330 4:00 pm
Nov
8
2023
"Ultra Wide Bandgap Semiconductors and Interfaces for High Power Electronics"
Abstract: Ultra Wide Bandgap Semiconductors (UWBS) have been identified as crucial materials for a new generation of power electronics that would enable the future electricity grid. The UWBS materials of AlN, cubic BN and diamond exhibit high carrier mobility and high thermal conductivity which would support high power electronics. Interfaces of different UWBS must encompass the different crystal structure (cubic vs wurtzite), the different chemical bonding (III-V vs group IV), and the interface electric field (polarization and piezoelectric effects). This talk presents progress on doping of diamond, high current transport in undoped diamond, noise spectroscopy to characterize electrical defects, comparison of polarization and charge transfer for interface doping for transistors, and the challenge of electrical contacts.
Speaker Bio: Robert Nemanich is Regents’ Professor in the Department of Physics at Arizona State University. He leads the DOE EFRC on ULTRA Materials for a Resilient Smart Electricity Grid. His research is focused on growth, interfaces and phenomena of diamond and ULTRA materials.
Darrin Communications Center (DCC) 330 4:00 pm
Nov
1
2023
“Developing optical material platforms for quantum and AI technologies.”
The recent breakthroughs in optical material research led to new application capabilities in information processing, including quantum simulation and photonic deep neural networks.
In the first part of my talk, I will present our proposal and experimental demonstration of using metamaterial, artificial composite materials, to manipulate single-photon quantum interference, which is the central operation unit in photonic quantum information processing. We show the dynamical and continuous control over the quantum photon-photon interactions (between single photons) from bosonic to fermionic, impossible by traditional optics. In the second part of my talk, we build strong coupling of the photon with semiconducting excitonic halide perovskites in the high-quality optical cavity. With this device, we explore analog quantum emulation, which is traditionally widely believed can only be performed with ultracold atoms. I will show the construction of XY spin Hamiltonian and superfluidity using our photonic room-temperature platform.
In the final part of the talk, I will switch gears and introduce our collaborative efforts in experimentally demonstrating the first optical neural network devices based on 2D materials. This is achieved by implementing intrinsic synergistic transitions in 2D materials to enhance and modulate the nonlinear signals of the devices.
Some of my research plans at RPI will also be briefly discussed.
Dr. Wei Bao is currently an assistant professor of materials science and engineering at RPI. Previously, he was an assistant professor of electrical and computer engineering at the University of Nebraska-Lincoln. He received his B.S. in physics (minor in chemistry) at Peking University, followed by the completion of his Ph.D. in materials science and engineering at the University of California, Berkeley. After graduation, he did his postdoc at UC Berkeley's Nanoscale Science and Engineering Center until 2019. Dr. Bao's current research interests broadly focus on optical materials. He is a recipient of the NSF CAREER Award in 2022 and the Rising Star of Light 2022 Award by the Nature Portfolio journal, Light: Science and Application.
Darrin Communications Center (DCC) 330 4:00 pm
Oct
25
2023
“Ultrafast dynamical processes in quantum materials.”
Abstract: Low-dimensional (e.g., atomically thin) continues to gain prominence in applications ranging from electronics to photonics and energy conversion systems. Critical to efficiently developing these systems is the understanding of the fundamental processes related to the dynamics of charge carriers, phonons, and other excitations (i.e. excitons, polaritons). Understanding the principles that govern these excitations will enable the fabrication of optoelectronic and photonic devices with novel and enhanced functionalities. While significant studies of nanomaterials, optical, and electrical transport properties are often made, identifying the mechanisms and timescales governing the interactions between electrons, phonons, and other excitations can be extremely challenging. I will discuss how excited carriers in low-dimensional systems undergo energy relaxation through various dynamical processes that occur over different time scales. Various physical mechanisms such as electron-phonon interactions, phonon-phonon interactions, and carrier recombination are involved in these processes. The electron‒phonon scattering processes are essential to understanding and controlling the energy and charge flow in electronic and energy conversion devices. For this study, we used time-resolved pump-probe spectroscopy with subpicosecond resolution to observe charge carrier dynamics in bilayer graphene.
Bio: Dr. Ioannis Chatzakis earned his Ph.D. in Physics from Kansas State University in Dec. 2009. After completing his coursework, he moved to Columbia University to work on the optical and electronic properties of carbonic materials under the supervision of Prof. Tony F. Heinz. He also holds an M.Sc. degree in Physical Chemistry (Applied Molecular Spectroscopy), and a B.Sc. degree in Electrical Engineering. Before joining TTU, he was an American Society for Engineering Education (ASEE) research fellow residing at the U.S. Naval Research Laboratory (NRL) in Washington, DC. Prior to the NRL appointment, he trained as a postdoctoral researcher at Iowa State University/Ames Laboratory, Stanford University, and the University of Southern California (USC). He is a member of the American Physical Society, Materials Research Society, and Optical Society of America, and he serves the community as a referee in several scientific journals.
Darrin Communications Center (DCC) 330 4:00 pm
Oct
18
2023
"A Social Network Analysis (SNA) approach on why and how LGBT+ and women stay in physics."
Part of a successful career trajectory in physics is building and maintaining a professional network of peers, collaborators, and mentors that supports one’s professional growth and advancement. Building these networks can be challenging for minoritized groups, such as women and LGBT people, and may be one of the reasons leading to the challenges they face in physics. This study applies qualitative Social Network Analysis (SNA) to better understand how these groups build their social networks and the impact of these networks on their careers. In this presentation we focus on experiences contributing to the permanence of women and LGBT physicists in the field of physics, discussing how people in different sectors talk about their trajectories, challenges and ways how their institutions supported (or not) their identities and professional advancement.
Dr. Camila Amaral, University of Utah
Darrin Communications Center (DCC) 330 4:00 pm
Oct
11
2023
“AI guided materials discovery of two-dimensional magnets”
The discovery of van der Waals (vdW) materials with intrinsic magnetic order in 2017 has given rise to new avenues for the study of emergent phenomena in two dimensions. In particular, monolayer CrI3 was found to be ferromagnet. Other vdW transition metal halides were later found to have different magnetic properties. How many vdW magnetic materials exist in nature? What are their properties? How do these properties change with the number of layers? A conservative estimate for the number of candidate vdW materials (including monolayers, bilayers and trilayers) exceeds ~106. A recent study showed that artificial intelligence (AI) can be harnessed to discover new vdW Heisenberg ferromagnets based on Cr2Ge2Te6 [1,2]. In this talk, we will harness AI to efficiently explore the large chemical space of vdW transition metal halides and to guide the discovery of magnetic vdW materials with desirable spin properties.That is, we investigate crystal structures based on monolayer Cr2I6 of the form A2X6, which are studied using density functional theory (DFT) calculations and AI. Magnetic properties, such as the magnetic moment, are determined. The formation energy is also calculated and used as a proxy for the chemical stability. We show that AI combined with DFT can provide a computationally efficient means to predict the thermodynamic and magnetic properties of vdW materials [3]. This study paves the way for the rapid discovery of chemically stable magnetic vdW materials with applications in spintronics and data storage.
[1] T. D. Rhone, et al., “Data-driven Studies of Magnetic Two-dimensional Materials,” Scientific Reports 10, 15795 (2020).
[2] Y. Xie, et al., “Data-Driven Studies of the Magnetic Anisotropy of Two-DimensionalMagnetic Materials,” J. Phys. Chem. Lett., 12, 50, 12048–12054 (2021).
[3] T. D. Rhone et al., “Artificial Intelligence Guided Studies of van der Waals Magnets,” Adv. Theory Simulations, 6, 2300019 (2023).
This research was primarily supported by the NSF CAREER, under award number DMR-2044842.
Darrin Communications Center (DCC) 330 4:00 pm
Oct
4
2023
"A Brief Introduction to the Baryon Circulation Process in the Local Universe"
Have you considered that the air you just breath in and out was once circulated through the Solar System, the Milky Way, and the vast space encompassing billons of stars long time ago? This air is part of the Cosmic Baryon Cycle that flows in and out of a galaxy such as the Milky Way and governs the future fate of the galaxy. Over millions or billions of years, baryonic inflows replenish galaxies to form new stars, while outflows from galaxies erupt like powerful volcanos. In this talk, I'll showcase recent research efforts to capture baryons flow in and out of galaxies in action using large telescopes such as the Hubble and high-resolution hydrodynamical simulations.
Darrin Communications Center (DCC) 330 4:00 pm
Sep
27
2023
Time-domain Paradigm of Analog and RF Design using Advanced CMOS Technology
Abstract: Analog and RF circuits have been traditionally designed using continuous-time operation in voltage domain. With the scaling down of transistors and move to the FinFET technology, this is no longer possible without ruining the performance and power consumption. On the other hand, the low supply voltage and sheer switching speed of transistors favor the newly developed time-domain operation where the signal information is contained not in a voltage level but in a time transition timestamp. This talk will give an overview of such recent advancements in the main areas of a communication channel: 1) frequency synthesizer exploiting all-digital PLLs using digital-to-time converters (DTC) and charge-sharing locking techniques; 2) digital transmitters exploiting switched-mode power-amplifier stage even at mm-wave; 3) discrete-time receivers manipulating the signal as charge packets that undergo extensive charge-sharing for filtering and decimation.
Biography R. Bogdan Staszewski received B.Sc. (summa cum laude), M.Sc. and PhD from University of Texas at Dallas, USA, in 1991, 1992 and 2002, respectively. From 1991 to 1995 he was with Alcatel in Richardson, Texas. He joined Texas Instruments in Dallas, Texas in 1995. In 1999 he co-started a Digital RF Processor (DRP) group in TI with a mission to invent new digitally intensive approaches to traditional RF functions. Dr. Staszewski served as a CTO of the DRP group between 2007 and 2009. In July 2009 he joined Delft University of Technology in the Netherlands where he is currently a part-time Full Professor. Since Sept. 2014 he has been a Full Professor at University College Dublin (UCD) in Ireland. He has co-authored seven books, 11 book chapters, and over 160 journal and 220 conference publications, and holds 210 issued US patents. His research interests include nanoscale CMOS architectures and circuits for frequency synthesizers, transmitters and receivers, as well as quantum computers. He is a co-founder of a startup company Equal1 Labs aiming at building the first practical CMOS quantum computer. He is an IEEE Fellow and a recipient of IEEE Circuits and Systems Industrial Pioneer Award (https://ieee-cas.org/society-achievement-award-recipients-list).
Darrin Communications Center (DC) 330 4:00 pm
Sep
13
2023
Utilizing Nonperturbative Methods to Study CFTs and the AdS/CFT Correspondence
Perturbative methods and phenomena are ubiquitous in theoretical physics as they give us some analytic control over a problem. One drawback is the models or scenarios needed to perform such calculations are usually special, and thus limit the scope of applicability to more complicated, real-world systems. In this talk I will discuss some methods to study nonperturbative phenomena my collaborators and I have used to study conformal field theories (CFTs) and the AdS/CFT correspondence. This mainly includes utilizing lattice methods in hyperbolic space. I will briefly talk about how this can (and has) been put on a quantum computer, as well as other similar research we are working on.
Dr. Cameron Cogburn , Rensselaer Polytechnic Institute
Darrin Communications Center (DCC) 330 4:00 pm