Abstract: Strongly correlated and topological phases in condensed matter systems are at the cutting edge of fundamental physics studies, as well as being promising candidates for the next generation of technological capabilities like quantum computing. In recent years, a remarkable amount of progress has been made in creating and controlling such phases by introducing a small twist angle or lattice mismatch between two-dimensional (2D) materials. These systems, called moiré systems, have facilitated the surprising discovery of strongly correlated phases where one might not expect them (e.g. superconductivity in “magic-angle” twisted bilayer graphene) or long-sought new physics (e.g. the fractional quantum anomalous Hall effect (FQAHE) in twisted MoTe2). However, much of the work in this rapidly developing field have focused on the case where the constituent 2D materials of the moiré system are monolayers, or at most bilayers. I will show that this restriction to one or two atomic layers is unnecessarily limiting. Surprising new phenomenology can be realized in graphitic moiré systems, where at least one component is three-layers or more. Most notably, we find that a new type of “moiré enabled” electron crystallization can occur that spontaneously breaks the moiré translational symmetry and has dissipationless edge modes, analogous to a topological version of a Wigner crystal. Our results suggest that these topological electron crystals 1) are at least somewhat common across multilayer graphene moiré systems, 2) can have uniquely tunable magnetization states, and 3) closely compete with the newly discovered FQAHE. Understanding this competition, as well as the novel phenomenology of the topological electron crystal phase, will be of fundamental interest in future studies of strongly correlated topological systems. 

We have developed a new cloud model, CARMA Cloud, for the NCAR Community Earth System Model that is designed to simplify the cloud model and improve its representation of cloud aerosol interactions. Rapid, unexpected, global warming since 2003 seems to be due to a combination of cloud feedback to global warming and strong response to aerosol changes. While the model is currently aimed at terrestrial cloud physics, the basic code has recently been used for exo-planet studies, and an early version of the model was used for studies of Martian ice clouds.

All current climate models assume that rain and snow are separate entities and can be represented with minimal information such as cloud mass and particle numbers. The Community Aerosol and Radiation Model for Atmospheres, CARMA, instead, computes the particle size distributions for the clouds which unites cloud and rain, as well as ice crystals and snow. The model also includes dust and sulfate aerosols inside of the ice clouds, one step towards improving cloud aerosol interactions.

CARMA shows, in agreement with observations, that there is a continuous distribution of particles between rain and cloud as well as ice and snow, showing the major assumption of cloud and rain with distinct modes in other cloud models is wrong. In addition, it shows that satellite data from MODIS do not span a wide enough size range to measure cloud mass. Therefore, the disagreement between models, showing liquid water content rises with cloud number density, and satellite observations showing the opposite, is likely due to misinterpreting the satellite data.

The global albedo of the modeled clouds is very sensitive to details of the calculation of rain formation, and to the interaction of clouds and aerosols. In the model, we tune several key parameters (aerosol activation, coagulation/coalescence kernel) to create the best case that’s in alignment with observations regarding liquid/ice water path, liquid/ice water content, and radiative properties.

Continued evolution of the model is expected to make the cloud aerosol interactions more realistic and to improve computational eWiciency.

The Department of Physics at the University of Colorado Boulder in collaboration with CUbit and JILA is hosting the third annual Physics and Quantum Career & Internship Fair on Friday, October 17^th from 12:00 - 3:00 p.m. in the Glenn Miller Ballroom.

This event will feature employers across all areas of theoretical, experimental, and computational physics. The fair will connect physics undergraduate and graduate students and recent alumni with laboratory and industry leaders to learn about internships and employment opportunities.

Sign up online

Handshake is CU's online recruiting tool used by thousands of employers. It is recommended, but not required for students to sign up for the 2025 Physics and Quantum Career Fair on Handshake.

Abstract:  Interacting electrons in strong magnetic fields give rise to rich phenomena, exemplified by the quantum Hall effect. In rhombohedral graphene, remarkably similar behavior has been observed even without an external field. In this talk, I will describe how electron–electron interactions in this system can spontaneously generate giant effective magnetic fields, reaching hundreds of Tesla. These emergent fields originate from self-organized layer-skyrmion textures, whose dynamics give rise to distinctive collective shape modes that can be experimentally probed. Strikingly, much of this physics can be captured analytically in an “ideal limit”, revealing precisely how interactions can reproduce the essential ingredients of quantum Hall physics - without any external magnetic field.

Abstract: Non-methane volatile organic compounds (NMVOC) are emitted into the Earth’s atmosphere by varied biogenic and anthropogenic sources. Though the concentrations of these compounds are minute, they exert an outsized influence on atmospheric composition, primarily through their oxidation chemistry. This chemistry leads to the formation of key secondary species including tropospheric ozone, a harmful pollutant, and secondary organic aerosol (SOA), a key component of atmospheric particulate matter with implications for climate and air quality. Oxidation chemistry is a dense web of interconnected reactions. The branch points in this web are reactive intermediates: short-lived, open-shell species that often have several chemical removal pathways available to them. Peroxy radicals, RO2, formed from the reaction of alkyl radicals and molecular oxygen, are key intermediates in the atmospheric oxidation process. In the atmosphere, RO2 generally have 4 pathways available to them: 1) reaction with NO, 2) reaction with HO2, 3) isomerization, and 4) self- or cross-reactions. The relative importance of these pathways is often determinative of the ultimate outcomes of oxidation chemistry, affecting the extent to which oxidation results in the formation of secondary species, including ozone and SOA. Our group uses a variety of model-informed experimental approaches to investigate the fates of atmospheric peroxy radicals and their impacts on atmospheric composition. In this talk, I will focus on a series of recent, unconventional environmental chamber experiments designed to probe the product distributions that arise from isomerizations and self- or cross-reactions or single isomers of RO2.  These pathways remain uncertain, and have only recently been appreciated as important in the formation of secondary organic aerosol. Studying these pathways has proven challenging in traditional environmental chamber experiments due to coupling of oxidant generation with generation of HO2 or NO. To circumvent this, we use direct photolytic approaches to the generation of RO2. Here, an organic precursor with a photolabile functional group is introduced into an environmental chamber and photolyzed under UV lamps, yielding a single-isomer alkyl radical, which then reacts with O2 to form RO2. This simplifies downstream chemistry, and removes the need for an oxidant, giving greater control over experimental conditions and allowing for experiments where pathways 3 and 4 are the dominant fates of RO2. In parallel, we use a modified version of the Framework for 0D Atmospheric Modeling (F0AM) to select experimental conditions, tuning competition between different RO2 fates. By examining product distributions and kinetics, we examine the role of reactivity conditions and RO2 structure in determining RO2 fate and its impacts on downstream product formation and atmospheric composition. Further, I will discuss several computationally-informed environmental chamber experiments that are focused on finding so-called “uncanonical” reactions of RO­2, that is, reactions that involve molecular processes not typically considered for simple RO2 radicals. Using automated reaction mechanism generation, we identify several novel reactions of functionalized RO2. We perform carefully designed environmental chamber experiments with the goal of identifying products that are signatures of these unconventional pathways. The results are highly suggestive of these previously unexplored pathways, but also illustrate the extent to which a mechanistic understanding of atmospheric oxidation remains incomplete, motivating future work in this area.

The corona is a layer of hot plasma that surrounds the Sun, traces out its complex magnetic field, and ultimately expands into interplanetary space as the supersonic solar wind. This complex and unpredictable system varies over many orders of magnitude in space and time, so it's not surprising that we still do not have a complete theoretical understanding of its origins. In this talk, I will present some new observations and theoretical concepts that are helping us get closer to finally identifying and characterizing the physical processes responsible for the corona and solar wind. This will involve data from ground-based telescopes such as DKIST, space telescopes that observe in UV and X-ray wavelengths, and interplanetary probes such as Solar Orbiter and Parker Solar Probe. The theoretical concepts involve waves, turbulent eddies, and their evolution together with particles in collisionless plasmas. I hope to also discuss how this work feeds into the practical world of "space weather forecasting" and how it is being extended to better understand the high-energy activity and dynamic outflows of other stars. There are many lessons to be learned from the decades of advancements that came before us, and I will highlight some insightful work from my own mentors. Also, I am excited to talk about the great work being done on these topics by CU Boulder students. Lastly, I will conclude with future plans, including a brief review of new instruments over the next decade that will help us test (i.e., conclusively validate or falsify) our fanciful theoretical ideas.

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The Moon offers multiple types of resources. It is a scientific resource, an exploration resource, and also a commercial resource. The Moon is a cornerstone for multiple science disciplines, not just lunar; it can help us learn how to effectively explore further into the Solar System with humans and robots, and it can enable commercial activities that support science and exploration. Intuitive Machines has conducted two lunar surface missions, including the first commercial landing in February 2024. In this talk, I will discuss the value of the Moon as well as present details on past and future IM missions, as well as other upcoming activities

Control of spin and valley polarizations opens opportunities for spintronic and quantum information applications. Monolayer transition-metal dichalcogenides (TMDs) offer an appealing platform to harness such polarizations. TMDs host excitons in valley-shaped regions of their band structure, featuring well-defined carrier spins and obeying chiral optical selection rules. However, the technological potential of excitons in TMDs is impeded by rapid spin–valley relaxation.

I will present our theoretical/computational efforts to address and enhance spin–valley polarizations in TMDs through strong coupling to photons. Recognizing that chiral light is a manifestation of photonic spin, I will show such strong coupling to allow for efficient spin transduction through the formation of "chiral polaritons". I will furthermore show how a breaking of chiral symmetry in optical cavities allows valley–spin relaxation to be suppressed in embedded TMDs.

I will also discuss our efforts to unravel how spin–valley relaxation in TMDs is driven by lattice phonons. Towards this goal, my group has advanced nonadiabatic methodologies that allow delocalized phonon modes and topological effects to be incorporated within a mixed quantum–classical framework. Results for TMDs indicate this approach to enable the modeling of solid-state phonon-driven processes at realistic dimensionalities.

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The Hubble Space Telescope story has been a fascinating study in public policy, engineering, ethics, and science. The Hubble is perhaps the most productive scientific instrument ever created by humans. In May 2009, a team of astronauts flew to the Hubble Space Telescope on space shuttle Atlantis. On their 13-day mission and over the course of 5 spacewalks they completed an extreme makeover of the orbiting observatory. They installed the Wide Field Camera-3, the CU/Boulder Cosmic Origins Spectrograph, repaired the Advanced Camera for Surveys and the Space Telescope Imaging Spectrograph, as well as a number of maintenance activities. These Hubble spacewalks are considered the most challenging and complex efforts ever of people working in space. Now, 16 years later the Hubble is still going strong. Building on the servicing heritage of Hubble the Habitable Worlds Observatory is in the initial planning stages and promises to be a worthy successor to Hubble. As part of the design the Habitable Worlds Observatory will be serviceable, albeit by robotic means. The adventures of Hubble servicing and the future servicing of Habitable Worlds will be presented in this talk.

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Mid-Infrared (MIR) light can interact with molecules by selectively exciting molecular vibrational modes. In combination with photonic structures, MIR can target specific vibrational states of molecular to influence chemical reactions. In this talk, I will explain how photonic environments can modify molecular dynamics through strong light-matter coupling. This strong coupling leads to the molecular vibrational polaritons – a hybrid quasiparticle between light and matter. Using two-dimensional infrared (2D IR) spectroscopy, we have demonstrated that strong coupling to photonic environments can efficiently promote energy transfer within or between molecules, subsequently slowing down competing reaction pathways. We further explored the criteria to fulfill polariton-enabled energy transfer, by which we discovered and verified a new principle to enable intermolecular energy transfer through polaritons in disorder materials. Lastly, we employed a polariton propagation experiment to determine the number of active polariton states versus the inactive dark states. This research progress provide insights into a rational mechanism and designing photonic structures to modify chemical landscapes and influence reaction pathways.

The Department of Biochemistry invites professors and scientists from other universities and institutes to present seminars at the University of Colorado Boulder throughout the academic year. These seminars provide an opportunity for faculty and students to learn about exciting current research.

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The Department of Biochemistry invites professors and scientists from other universities and institutes to present seminars at the University of Colorado Boulder throughout the academic year. These seminars provide an opportunity for faculty and students to learn about exciting current research.

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Abstract: Modeling gas-phase chemical kinetics relevant to combustion and atmospheric chemistry requires a complete description of elementary reactions involving ephemeral species such as hydroperoxyalkyl radicals, Q̇OOH, which undergo competing sets of unimolecular reactions and bimolecular reactions with O2. The balance of flux from the competition affects rates of chain-branching and inherently depends on temperature, pressure, and oxygen concentration. Accordingly, the influence of [O2] on species formed via reactions of O2 with carbon-centered radicals (Ṙ), and the subsequent fate of Q̇OOH and related products, is central to developing accurate chemical kinetics mechanisms. However, reactions consuming intermediates from Ṙ + O2 are often simplified to such a degree that mechanism truncation error (uncertainty derived from incomplete reaction networks) becomes significant and precludes high-fidelity simulations of chemical systems for sustainable transportation energy.

Intermediates produced from Ṙ + O2 reactions of hydrocarbons and biofuels include cyclic ethers and alkene isomers, which are shown to undergo two unique types of reactions that are neglected in current gas-phase combustion models: (1) non-Boltzmann reactions, wherein rovibrationally excited radicals produced during H-abstraction undergo prompt ring-opening prior to collisional stabilization, and (2) stereochemical-dependent reaction pathways originating in closed-shell cyclic ethers that follow from the preceding ring-closing transition state [Q̇OOH]≠ and from subsequent cyclic ether peroxy radicals, both of which can facilitate new reaction channels including chain-branching pathways.

To ameliorate predictive deficiencies, results from a coupled experimental-computational workflow are outlined wherein sub-mechanisms, informed by speciation experiments, are developed and utilized as input into AutoMech, an open-source code for quantum chemical mechanism development. AutoMech is employed to calculate ab initio thermochemical and rate coefficeints for all species and reaction pathways in an initial mechanism. Elementary reactions are translated by AutoMech from 2D descriptions into stereochemically-enumerated representations. Potential energy surfaces are calculated using explicitly-correlated coupled-cluster energies with dispersion-corrected double-hybrid density functional theory geometries and frequencies. Master equation theory is used to calculate pressure- and temperature-dependent rate coefficients and partition functions for each reaction and species including for non-Boltzmann reactions. Results discussed include ongoing projects on species derived from cyclopentyl radicals and alkyl-substituted cyclic ethers produced from pentyl radical isomers. 

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The Department of Biochemistry invites professors and scientists from other universities and institutes to present seminars at the University of Colorado Boulder throughout the academic year. These seminars provide an opportunity for faculty and students to learn about exciting current research.