Physics Colloquia

How did the first living cells come into being from the earth’s molecular soup about 4 billion years ago? Despite much speculation – maybe RNA molecules came first, or proteins, or chemical networks – there’s not yet a consensus origins story. We’ve taken a new look, from a physics perspective around three problems. First, before addressing what molecules came first — the chicken and egg problem — we must address the more fundamental question: What was the driving force? What was the autocatalytic dynamics, i.e. the “flywheel” of evolution that started choosing materials in the first place? Second, how did sequence-structure-function arise from random polymers? It’s a “needle-in-a-haystack” statmech problem. Third, what was “fitness” before there was biology? Chemistry doesn’t have such a thing. We have developed theory and simulations, and some experiments, showing how short random proteins could bootstrap their way towards biology.

We plan to construct the next generation of colliders because there is new fundamental knowledge to be gained at the energy frontier — knowledge about both the Standard Model itself and the more fundamental theory that underlies it. I’ll survey the triumphant role of colliders in building the Standard Model, the main open questions now facing particle physics, and the profound motivation these questions provide for successors to the Large Hadron Collider. Among these successors, I’ll devote particular attention to a qualitatively new accelerator complex: a high-energy muon collider. Such a collider, potentially at Fermilab, would powerfully complement experiments across the frontiers of particle physics and chart a convergent path into the future.

The dogma of band engineering in semiconductor heterostructures is that electronic properties can be tailored by combining dissimilar materials with nearly identical lattice constants. Covalent bonding during epitaxial growth registers lattices, and yields crystals with a wide variety of useful and tunable properties. The advent of van der Waals heterostructures of two-dimensional (2D) materials has added a new tool to electronic materials design, namely that of controlling the twist angle between different 2D crystals in a heterostructure. This in turn has opened avenues to tailor interaction and topology in twist-controlled van der Waals heterostructures. This presentation will describe experimental advances in the realization of twist-controlled van der Waals heterostructures, with examples from twist-controlled double layers with independent contacts, and twist-controlled moiré patterns of graphene.

Educational innovation is pushing towards providing students with authentic learning experiences. But what counts as authentic? In this talk, I’ll discuss the various ways we’ve been conceptualizing authenticity in introductory physics labs, from simulating authentic practice to embedding the lab exercises in more advanced physics topics, such as particle physics and active matter. We’ll discuss preliminary data about student learning and perceptions and explore future research questions.

Educational innovation is pushing towards providing students with authentic learning experiences. But what counts as authentic? In this talk, I’ll discuss the various ways we’ve been conceptualizing authenticity in introductory physics labs, from simulating authentic practice to embedding the lab exercises in more advanced physics topics, such as particle physics and active matter. We’ll discuss preliminary data about student learning and perceptions and explore future research questions.

https://physics.umd.edu/~yakovenk/
As a postdoc, I attended a physics colloquium presented by Sergei Kapitza at Rutgers University in the fall of 1992. His talk argued that human population growth is hyperbolic with a singularity in the year 2026. Actually, this claim was first published in Science by Heinz von Foerster et al. in 1960. Using current empirical data from 10,000 BCE to 2023 CE, we re-examine this claim. We find that human population initially grew exponentially in time as N(t)~exp(t/T) with T~3000 years. This growth then gradually evolved to be super-exponential with a form similar to the Bose function in statistical physics. Population growth further accelerated around 1700, entering the hyperbolic regime N(t)=C/(t_s-t) with the extrapolated singularity year t_s=2030, which essentially confirms the claim by Kapitza and von Foerster et al. We attribute the onset of the hyperbolic regime to the transition to massive use of fossil fuels upon the Industrial Revolution, as evidenced by a linear relation that we find between population and the increase in CO2 level from 1700 to 2000. But in the 21st century, the inverse population curve 1/N(t) deviates from a straight line and follows a pattern of "avoided crossing". As a result, the singularity transforms into a square-root Lorentzian peak of the width \tau=32 years. The predicted year t_s=2030 of the peak in human population is much earlier than in other demographic forecasts. We also find that the increase in the CO2 level since 1700 is well fitted by arccot[(t_s-t)/\tau_F] with \tau_F=40 years, which implies a Lorentzian peak in the annual emissions d(CO2)/dt at the same year t_s=2030.
Publication: V. M. Yakovenko, Physica A 661, 130412 (2025)
https://doi.org/10.1016/j.physa.2025.130412 (open access)
Video recording: https://www.youtube.com/watch?v=kJPFApdokrg

The Anderson-Higgs mechanism manifests in quantum materials, with the Meissner effect in superconductors serving as a notable example. Here, photons gain mass through interactions with condensed Cooper pairs, leading to the expulsion of magnetic fields from the superconductor's interior. A similar process has been predicted to occur in a charge density wave (CDW) condensate, where the collective phase oscillations (phasons), which are typically massless, could acquire mass via a Anderson-Higgs-like mechanism. Although the concept of massive phasons was proposed decades ago, it is only recently that THz emission from the unconventional CDW insulator (TaSe4)2I has been detected and linked to this mode. To directly confirm the presence of these massive phasons, local charge oscillations must be measured with femtosecond temporal resolution, which is a challenging task.
In this talk, I will present a pump-probe scanning tunneling microscope that enables local measurement of local charge dynamics. Using this tool, we observe charge oscillations at 0.22 THz, displaying the temperature dependence expected of an excitation acquiring mass through the Higgs mechanism. Remarkably, we also detect a second excitation with equal intensity. I will present evidence that this mode results from the splitting of the massive phason into two massless modes, akin to the decay of a neutral pion into two photons. This work not only confirms the existence of Higgs-ed massive phasons in (TaSe4)2I but also uncovers their complex interactions with other modes, opening new avenues for exploring dynamic phenomena such as light-induced superconductivity.