2023

Apr
12
2023
Darrin Communications Center (DCC) 330 4:00 pm

Mar
29
2023
Darrin Communications Center (DCC) 330 4:00 pm

Mar
22
2023

Mar
1
2023
"Our Galaxy in motion: Ripples, ridges and spirals in the Milky Way"

Data from ESA’s Gaia mission is already revolutionizing Galactic astronomy, providing an unprecedented view of the Solar neighborhood and beyond. However, while it provides us a great opportunity to transform our understanding of the Milky Way, it has also highlighted how far from equilibrium our Galaxy is. The spiral pattern in vertical position vs. velocity is a signature of our Galaxy’s past interaction with perturbing influences such as merging dwarf galaxies, or internal substructure. We dissect and analyze these ‘phase spirals’, showing the first discovery of two armed ‘breathing spirals’ in the inner disc, and show how we can leverage high resolution galaxy models and dynamical theory to learn about the structure and history of our Galaxy.

 

Darrin Communications Center (DCC) 330 4:00 pm

Feb
15
2023
"Quasi-1D Topological Insulators"

The discovery of topological insulators (TIs) has created a revolution in condensed matter physics and beyond that is likely to continue having far ranging implications over coming decades. In this colloquium, I will introduce a new generation of TIs that are van der Waals semiconductors with two distinct stacking directions. In particular, I will elucidate why such quasi-1D TIs are superior to the quasi-2D (layered) ones, how they have realized experimentally the first weak TI and the first higher-order TI, with a room-temperature transition between the two extremely rare phases, and the ongoing efforts toward the realization of room-temperature quantum spin Hall effect and helical Luttinger liquid in their monolayer devices. The talk will be concluded with a model that unifies all the discussed TIs and an outlook on their future exploration.

Darrin Communications Center (DCC) 330 4:00 pm

Feb
8
2023
"Planetary Perspectives on the Emergence of Life"

We advocate for an alternative approach to life’s origins that conceives of the earliest prebiotic chemistry within the context of the fundamental planetary processes that defined the Hadean. Planetary evolution generated an array of localized and dynamic environments, each with specific physicochemical characteristics and dynamics that subsequently produced an even more extensive suite of abiotic chemistries. While some likely never generated organic molecules, others might have produced extensive organic inventories. In some cases, these chemistries and environments co-evolved, ushered along by planetary processes and local physicochemical conditions, eventually leading to life’s emergence.  Here we postulate a new paradigm for the study of life’s origins: Only through experimental and theoretic constructs that replicate dynamic early Earth environments can we understand the chemistry that arose during the Hadean, and this chemistry is, necessarily, the prebiotic chemistry that laid the foundation for life’s emergence. In this talk I will describe the Earth First Origins Project, which aims to apply a combination of experimental and virtual facilities to the question of life’s origins.  By developing new experimental and modelling platforms that more faithfully replicate early Earth conditions, we aim to explore various early Earth environments for their potential to host productive chemical reaction networks that could give rise to life on Earth.  We will explore a variety of prebiotic chemistries along the abiotic→prebiotic→biotic transition, from CO2 reduction through complex polymer selection.  I am also excited to introduce NASA’s broader initiative to reimagine origins of life research within the Prebiotic Chemistry and Early Earth Environments Consortium, and the many opportunities for global community participation.

Darrin Communications Center (DCC) 330 4:00 pm

2022

Nov
30
2022
Title and abstract to be annouced.

 

Abstract: In this conversation I represent the committee to share (1) various research funding  opportunities in the US, (2) example of merit review process in competitive proposals, (3) elements for success in pursuit of advanced degree in graduate study and beyond. This include but not limited to emotional intelligence and personal traits, and (4) the responsibilities of a student receiving financial support in research to the funding source and global scientific community.

Bio: Wang served as Physics Dept head form 2000-2010. Fellow of professional societies (APS, AVS, MRS, and AAAS). She enjoys teaching and hands-on research.

 

Juan Borja, Ph.D. , Rensselaer Polytechnic Institute
Darrin Communications Center (DCC) 4:00 pm

Nov
2
2022

Oct
12
2022
"Room-Tempretaure Rashba/Dresselhaus Effect in a Switchable Quantum Well"

We show the discovery of the persistent spin helix in an organic–inorganic hybrid ferroelectric halide perovskite whose layered nature makes it intrinsically like a quantum well. We demonstrate that the spin-polarized band structure is switchable at room temperature via an intrinsic ferroelectric field. We reveal valley–spin coupling through a circular photogalvanic effect in single-crystalline bulk crystals. The favoured short spin helix wavelength (three orders of magnitude shorter than in III–V materials), room-temperature operation and non-volatility make the hybrid perovskite an ideal platform for understanding symmetry-tuned spin dynamics, towards designing practical spintronic materials and devices that can resolve the control-relaxation dilemma.

Darrin Communication Center (DCC) 324 4:00 pm

Oct
5
2022
"MODELS POLITICAL POLARIZATION IN US CONGRESS AND PRESIDENTIAL ELECTIONS"

Our research was motivated by a highly disturbing puzzle. Confronted with a deadly global pandemic that threatened not only massive loss of life but also the collapse of our medical system and economy, why were we unable to put partisan divisions aside and unite in a common cause, such as the Great Depression and the Second World War that led to the national mobilization? We used a statistical physics model to search for an answer. The model reveals asymmetric hysteresis trajectories with tipping points that are hard to predict and that make polarization extremely difficult to reverse once the level exceeds a critical value. Political scientists have documented increasing partisan division and extremist positions pronounced more among political elites than among voters, raising a question how polarization might be attenuated. In the talk, we introduce a general model of opinion change to see if the self-reinforcing dynamics of influence and homophily may be characterized by tipping points that make reversibility problematic. The model applies to a legislative body or other small, densely connected organization, but does not assume country-specific institutional arrangements that would obscure the identification of fundamental regularities in the phase transitions. Agents in the model have initially random locations in a multidimensional issue space consisting of membership in one of two equal-sized parties and positions on 10 issues. Agents then update their issue positions by moving closer to nearby neighbors and farther from those with whom they disagree, depending on the agents’ tolerance of disagreement and strength of party identification compared to their ideological commitment to the issues. We conducted computational experiments in which we manipulated agents’ tolerance for disagreement and strength of party identification. Importantly, we also introduced exogenous shocks corresponding to events that create a shared interest against a common threat (e.g., a global pandemic). Phase diagrams of political polarization reveal difficult-to-predict transitions that can be irreversible due to asymmetric hysteresis trajectories. We conclude that future empirical research needs to pay much closer attention to the identification of tipping points and the effectiveness of possible countermeasures. Next, we focus on social media that is decentralized, interactive, and has been transforming political communication dynamics for over a decade. Using nearly a billion tweets, we analyze the change in Twitter’s news media landscape between the 2016 and 2020 U.S. Presidential elections. Using political bias and fact-checking tools, we measure the volume of politically biased content and the number of users propagating such information. We observe that the fraction of fake and extremely biased content declined between 2016 and 2020. We then identify influencers, users with the top ability to spread news in the Twitter network. The more influential 2016 users were, the higher was their rate of being active and keeping their ranks in 2020. We also analyze changes in influencers’ real-world affiliations, political biases, and in users’ choices as to which influencers to retweet and which ideology to support. Despite a decrease in extremely biased content and fake news on Twitter, results show increasing echo chamber behaviors and latent ideological polarization across the two elections at the user and influencer levels.

Darrin Communication Center (DCC) 324 4:00 pm

Sep
28
2022
"Making use of Non-Hermitian Spectral Degeneracies"

The topological structure associated with non-Hermitian spectral degeneracies known as exceptional points (EP) can provide tools for controlling the propagation of light and its interaction with matter. In this talk, I will briefly discuss the emergence of discrete EPs and the formation of exceptional surfaces (ES) - hypersurfaces on which every point is an EP-   in photonic systems, and then discuss some of our research outcomes: I will first discuss how an ES can be utilized for optical sensing and chiral perfect absorption [1]. Then, I will show the emergence of an EP in the interaction of THz light with an ensemble of molecules and how it affects the phase and amplitude of the THz light [2]. I will end my talk with a discussion of the opportunities and challenges in classical and quantum photonics with non-Hermitian settings.

 

[1] Soleymani et al. Nat Commun 13, 599 (2022).

[2] Ergoktas et al. Science 376, 184 (2022).

Darrin Communication Center (DCC) 324 4:00 pm

Sep
21
2022
“What it takes to succeed in graduate research and beyond?”

Interested attendees please bring a device (laptop or iphone) to access a web link to be provided in the talk.
 

Abstract: In this conversation I represent the committee to share (1) various research funding  opportunities in the US, (2) example of merit review process in competitive proposals, (3) elements for success in pursuit of advanced degree in graduate study and beyond. This include but not limited to emotional intelligence and personal traits, and (4) the responsibilities of a student receiving financial support in research to the funding source and global scientific community.

Bio: Wang served as Physics Dept head form 2000-2010. Fellow of professional societies (APS, AVS, MRS, and AAAS). She enjoys teaching and hands-on research.

Darrin Communications Center (DCC) 324 4:00 pm

Sep
14
2022
"Revisiting Nonlinear Optics using Structured light."

I will give an overview of the research that is taking place in my lab: I will introduce methods for generating, manipulating, and controlling structured lights as they interacts with nonlinear media , Biological samples, an applications in free space optical communication.  

Darrin Communication Center (DCC) 324 4:00 pm

Apr
20
2022
“Microchip Powered Terahertz Wave Absorption Spectroscopy for Gas Analysis”

Terahertz (THz) wave absorption measurements provide selective identification of gas molecules through their characteristic rotational spectra. The presentation describes the scientific foundation for quantitative gas analysis via THz wave absorption and a novel THz wave technology for gas spectroscopy relying on microchips capable of generating THz waves. The current research is focused on filling knowledge gaps in the THz spectroscopy database for gas species of interest in industry, the environment and health care, and undertakes the technology development necessary for electronic THz wave gas sensors with applicability as field instruments. The realization of the technology development requires a multidisciplinary approach that involves the disciplines of physics, electrical engineering, and combustion chemistry.

The implementation of a THz wave spectrometer operating in the 220 to 330 GHz frequency band using state-of-the-art electronic THz wave radiation sources and detectors will be outlined [1, 2]. The novel technology for THz wave gas phase spectroscopy has been successfully validated by the detection of a broad range of relevant volatile organic compounds [2], halogenated hydrocarbons [3], commercial refrigerants, and nitrogen compounds. The sensitivity of the spectrometer meets gas species detection limits set by, e.g. occupational health and safety standards. The large bandwidth (220 to 330 GHz), high frequency resolution (0.5 MHz), and rapid frequency scanning (160 GHz/s) of the spectrometer enables the important analysis of gas mixtures. Towards full miniaturization of the novel gas sensing technology a twin-FET (field effect transistor) THz wave detector monolithically integrated with a dual-feed antenna has been designed, fabricated, and tested. Fabricated in Global Foundries 22nm FD-SOI process, the detector covers a measured frequency range from 220 GHz to 300 GHz. The microchip THz wave detector was tested in the THz wave spectrometer and found to match the performance of state-of-the-art commercial Schottky detectors for the detection of a range of important volatile organic compounds.

Webex Meeting: https://rensselaer.webex.com/rensselaer/j.php?MTID=m55f4f03e022938f6851b48dc1d3fb88a 4:00 pm

Apr
13
2022
“Suspended 1D nanomaterials: synthesis via floating catalyst and direct assembly as high-performance network materials”

Fostering the enormous potential of nanomaterials requires assembling them as organized structures on a macroscopic scale. For 1D nanomaterials a natural embodiment is as aligned fibres or fabrics that efficiently exploit the axial properties of their constituents. This talk describes a method to produce macroscopic solids made of 1D nanostructured directly collected as they grow floating in the gas phase. The strategy consists in synthesising 1D nanostructures suspended in a gas stream using an aerosol of catalyst nanoparticles, i.e. via floating catalyst chemical vapour deposition (FCCVD). Under this synthesis mode, growth is ultrafast, around 1000 faster than in substrate-based processes. The resulting high aspect ratio (> 200) enables the aggregation of nanomaterials in the gas phase and ultimately the formation of network solids.

The first of the talk reviews the use of this synthetic route to produce different nanotubes (e.g. carbon nanotubes – CNTs) and nanowires (SiNW). It analyses the factors that control the different possible reaction path in FCCVD and introduces a basic kinetic model to rationalise aspects of the reaction inferred from analysis of the nanostructures. 

Next, the talk shows that some of these macroscopic ensembles behave as “macromolecular” networks with many unusual or superior properties compared to monolithic materials: fibres of carbon nanotubes have tensile mechanical properties above many high-performance polymer fibres; sheets of silicon nanowires are flexible and have high cyclability as lithium-ion battery anodes.

The final part of the talk discusses the formation of intercalation compounds by insertion of different intercalants in fibres of carbon nanotubes, including observation of elongated ordered domains of intercalant, measurements charge transfer and bulk transport properties.

References:

Tough sheets of nanowires produced floating in the gas phase, Materials Horizons 7, 2978-2984, 2020.

Tensile properties of carbon nanotube fibres described by the fibrillar crystallite model. Carbon 133, 44-52, 2018.

Eliminating Solvents and Polymers in High-Performance Si Anodes by Gas-Phase Assembly of Nanowire Fabrics. Advanced Energy Materials, 2022. DOI: 10.1002/aenm.202103469

Macroscopic yarns of FeCl3-intercalated collapsed carbon nanotubes with high doping and stability. Carbon 173, 311-321, 2021.

Webex Meeting: https://rensselaer.webex.com/rensselaer/j.php?MTID=md2ec8882cd26cc233d00a1816861d5cf

Meeting number: 2622 145 2999

Password: P7SehtHiq38

Juan Jose Vilatel, IMDEA-MAT Madrid
Webex 4:00 pm

Apr
6
2022
Webex Meeting: https://rensselaer.webex.com/rensselaer/j.php?MTID=m55f4f03e022938f6851b48dc1d3fb88a 4:00 pm

Mar
30
2022
"2D Lateral Heterostructures via Sequential Edge-epitaxy and Laser-Induced Chalcogen Exchange."

Atomically thin layers are known as two-dimensional (2D) materials and have attracted a growing attention due to their great potential as building blocks for a future generation of low-power and flexible 2D optoelectronic devices. Similar to the well-established 3D electronics, the development of functional 2D devices will depend on our ability to fabricate heterostructures and junctions where the optical and electronic properties of different compounds are brought together to create new functionalities. Vertical heterostructures can be produced by selective van der Waals stacking of different monolayers with distinct chemical composition. However, in-plane lateral heterostructures, where different materials are combined within a single 2D layer, have proven to be more challenging. During the formation of the hetero-junction, it is important to minimize the incorporation of undesired impurities and the formation of crystal defects at the junction that will impact the functionality of the 2D device. When fabricating periodic structures, it is equally important to control the domain size of each material.

Join by meeting number:
Meeting number (access code): 2621 911 8730 
Meeting password: 6A6ryAAGvX3

 

Webex: https://rensselaer.webex.com/rensselaer/j.php?MTID=mab56abe9a19ef82c80287a7c9acd83ab 4:00 pm

Mar
15
2022

Mar
3
2022
"Time for New Narratives - Negotiating Diversity and Equity in Physics"

The environment in research institutes, physics departments, and lecture halls appears to be quite homogeneous. A majority of physicists is white, healthy, heterosexual, and cis-male. Increasingly, this is understood as a problem. Scientific societies, academic workplaces and research institutes are starting to welcome diversity in physics and to create and promote an appreciative work environment for all physicists. Yet, diversity is not only a characteristic of people. In this talk we learn more about diversity, the theoretical concept and its dimensions. Diversity Studies is a framework to reflect on the reproduction of social inequalities. It can be understood as an eye opener for the gendered, classed and raced politics of knowledge-producing processes.


We will review empirical studies, which show why and how diversity is entangled with physics in many different ways. We reflect on the power of norms and exclusions in the culture, representation, and teaching of physics. We look, for example, at communications in research labs, educational settings at universities, physicists’ behavior at conferences, and contents of physics textbooks. Teaching physics is not only about educating factual physical knowledge but at the same time transmits representations and norms of physical talent, technological competence, heroes in the history of physics, presumptions of heterosexual normativity, and hegemonic masculinity to the students. In doing so, we encourage some (male, white, middle class,...) students and erect barriers for others (female, students of color, working class,…). We discuss strategies to invent and present new, positive narratives about diversity and physics in the 21st century. These strategies may help to create and promote physics as a more welcoming environment for everybody. Moreover, awareness and understanding of the results of Diversity Studies in physics will foster the development of contemporary physics.

Short CV:
Dr. Helene Götschel has an interim professorship for education and digitalization at the Institute for General and Vocational Pedagogy at Technical University of Darmstadt, Germany. Previously, she was Professor for Gender and Diversity in Engineering and Computer Science at the University of Applied Sciences and Arts, Hannover, Germany, where she taught physics and interdisciplinary courses to students in electrical, mechanical, and industrial engineering. In her lifelong learning process, she was trained in physics (with a focus on experimental particle physics), history of science, social history, higher education, and gender studies. Her transdisciplinary research explores the entanglement of gender, diversity and physics.

 

Via WebEx: https://rensselaer.webex.com/rensselaer/j.php?MTID=m55f4f03e022938f6851b48dc1d3fb88a 4:00 pm