Eric Sembrat's Test Bonanza

Abstract

The interaction between electromagnetic fields and condensed matter not only underpins much of modern technology, but also provides one of the most fundamental ways to study quantum materials. To this end, the ever expanding family of emerging phenomena in these materials calls for new electromagnetic probes working in unexplored parameter spaces. In this talk I will present two cases where deeply subwavelength probes provide new insights into physics at interfaces: the first metallic magnetic domain walls in a magnetic insulator discovered by near-field microwave microscopy, and the first direct recording of ultrafast charge transfer across a sub-nm van der Waals interface by time-domain THz emission spectroscopy. I will also discuss the exciting opportunities provide by combining several of these techniques to create the first extreme-broadband micro-spectroscopy system.

We are witnessing a revolution in which quantum phenomena are being harnessed for next-generation technology. A central challenge in this effort is to gain detailed insights in the behaviors of electrons and spins in quantum materials. In this context, quantum sensing technology realized with nitrogen vacancy (NV) center in diamond has emerged as a powerful probe of advanced materials and devices. Due to its ability to sense magnetic field with high spatial resolution over wide temperature and dynamic range, NV sensors enable the exploration of condensed matter phenomena in parameter space inaccessible to existing probes. In this talk, I will discuss our application of NV quantum sensing technology to study correlated electronic and spin phenomena. We have directly imaged, for the first time, the viscous Poiseuille flow of the Dirac fluid in neutral graphene, a finding that holds implication for other strongly correlated electrons such as those in high-T_c superconductors. Enabled by the NV platform, we have developed new capabilities for probing coherent spin-waves, which can be applied to study novel magnetic materials and spintronic devices, and a tool for charactering low-dimensional high-T_c cuprates without electrical contacts. Looking forward, I will highlight opportunities for advancing the frontiers of quantum materials and quantum technology enabled by NVs and other solid-state atomic qubits.

Studying quantum entanglement over the past decade has allowed us to make remarkable theoretical progress in understanding correlated many-body quantum systems. However in real materials electrons experience spatially random heterogeneities ("dirt") whose theoretical treatment, including strong correlations, has been a challenge. I will describe how synthesizing ideas from quantum information theory, statistical mechanics, and quantum field theory gives us new insights into the role of randomness in 2D correlated quantum spin ("qubit") systems, enabling us to understand a broad variety of experimental observations.

First I will outline our results in two theoretically controlled settings, showing that even weak randomness necessarily nucleates certain topological defects with free spins that control observable physics. Second I will describe how the theory predicts a scaling collapse of the temperature and magnetic-field dependence of the heat capacity that is consistent with experimental observations from multiple materials, suggesting that mild randomness in these materials leads them to exhibit usable long-range entanglement of distant spin pairs. Third I will describe how these results lead us to conjectures of general constraints ("Lieb-Schultz-Mattis theorems") on all possible behaviors of quantum magnets, even with randomness; this surprising connection is enabling our current research on interacting disordered topological insulators ("anomalous localization") and promises further applications to entanglement in quantum technologies and quantum materials.

Abstract

Dr. Tomberlin will discuss species interactions on ephemeral resources such as vertebrate carrion, decomposing plant material, living individuals, and animal wastes in order to better understand the mechanisms regulating arthropod behavior as related to nutrient recycling and protein production.

One facet of his laboratory, which could be of interest to those in attendance at this meeting, is dissecting quorum sensing by microbes and determining its role in regulating interkingdom interactions. His lab has demonstrated quorum sensing by bacteria partially regulates mosquito attraction to blood-meals, fire ant attraction to baits, and blow fly attraction and colonization of carrion. His laboratory, in collaboration with others, has also discovered the ecological relevance of a toxin produced by an environmental pathogen responsible for a neglected tropical disease.

Bio

Dr. Jeffery K. Tomberlin is a Professor, AgriLife Research Fellow, and Presidential Impact Fellow in the Department of Entomology at Texas A&M University. He is also the Director of the Forensic & Investigative Sciences Program at Texas A&M University, and the principle investigator of the Forensic Laboratory for Investigative Entomological Sciences (F.L.I.E.S.) Facility (forensicentomology.tamu.edu) at Texas A&M University.

Since arriving on campus at Texas A&M University in 2007, 14 Ph.D. and 20 M.S. students have completed their degrees under his supervision. In total, he has published numerous papers, proceedings, extension articles, book chapters, and books on decomposition with approximately 6,000+ citations to date. Dr. Tomberlin welcomes those that are interested in collaborating or gaining experience in sustainable agriculture or other areas of his research to visit the F.L.I.E.S. Facility.

Dr. Tomberlin is considered a global leader in research on the black soldier, which is revolutionizing sustainable waste management globally. In fact, this species of insect is considered the crown jewel of the insects as feed industry due to its ability to recycle organic waste and produce insect biomass that can be used as feed for livestock, poultry, and aquaculture. This species has been approved for use in such a capacity globally- including the USA & European Union. Studies published by Dr. Tomberlin serve as the cornerstone allowing for this insect to be industrialized globally, such as systems for captive breeding, pathogen, toxin, and antibiotic reduction, bioenergy production, feed trials, and system optimization through microbiology and genetics/genomics.

Abstract

In native states, animal cells are surrounded by either fluid or a biopolymer network. The cell-environment interactions critically regulate cell function, as well as collective cell motion. The key to this interaction is the biophysical forces that cells generate. In this talk, I will focus on experimental studies of single cell force regulation in two biological systems. One is on tumor cell-extracellular matrix (ECM) interaction, in which we find that cell-ECM interacts reciprocally, cell traction force stiffens the matrix, and matrix in return, promotes cell force generation. Implications of this two-way cell-ECM interaction in tumor invasion will be discussed. In a second example, we studied how sperm cells swim against fluid flows guided by a hydrodynamic force. Interestingly, in both cases, biological matrices/fluids enhance force transmission range and promote cell-cell interaction.  

The detection of neutrinos with IceCube has cracked open a new window in astrophysics at the TeV-PeV energy scale. The revelation of a relatively hard neutrino spectrum and the unknown origin of the flux are two motivations to extend neutrino measurements to even higher energies, the ultra-high-energy (UHE) regime above 1e7 GeV. Another reason to build UHE neutrino detectors is cosmogenic neutrinos, which hold the key to the composition of UHE cosmic rays and their sources. Furthermore, by combining measurements from detectors that are sensitive to different neutrino flavors, it will be possible to search for new fundamental particle physics beyond the standard model.

The seemingly preferred way to search for UHE neutrinos nowadays is with radio detectors employed in ice (e.g., ARA and ARIANNA), on balloons (ANITA), or by pointing antennas at mountainous terrain (GRAND). An alternative detection technique is imaging of air showers. These instruments are sensitive to the Cherenkov and fluorescence emission from neutrino induced particle showers in the atmosphere.   In this talk, I show that imaging detectors are a viable and more cost-effective alternative UHE neutrino instruments if appropriately designed. In this talk, I present the design of TRINITY, a system of six Cherenkov telescopes. I discuss the sensitivity of the system, how to build it, and address operational constraints.

Abstract

Terrestrial animals are faced with the challenge of moving their center of mass using finite leg contacts — and this constraint is most severe in bipedal gaits, where no more than two leg contacts are possible in each stride of locomotion. Conceptual models of locomotion, such as the inverted pendulum (IP) and the spring-loaded inverted pendulum (SLIP) represent a dichotomy between rigid-legged walking and compliant running. However, a more general framework is needed to understand the compliant bipedal walking gaits used by humans and birds. d’Alembert’s principle of ‘virtual work’ can be used to determine the dynamics of locomotion by analyzing the relationship between the velocity of the center of mass and the force acting upon it. We apply this approach to show how humans are able to walk faster and more economically than other bipeds, including birds, robots, and simple models. Humans achieve a nearly constant mechanical cost of transport by increasingly rotating force and velocity vectors toward orthogonal to reduce work as walking speed increases. In contrast, ostriches reach only moderate walking speeds before transitioning to a grounded running gait that rotates force and velocity vectors away from orthogonal, as seen in a SLIP. Understanding dynamic strategies used by bipedal humans and birds can guide inquiry into structure-function relationships of fossil hominids and non-avian theropods, as well as informing the design and control of legged robots or robotic prosthetic and assistive devices.

Abstract

What is the critical load required to crush a soda can or a space rocket shell? Surprisingly, there is no good way to estimate it, because of the high defect-sensitivity of the buckling instability. 

Here we measure the response of (imperfect) soda cans to lateral poking and identify a generic stability landscape, which fully characterizes the stability of real imperfect shells in the case where one single defect dominates. 

By using this new paradigm, I will show how we can accurately and non-destructively predict the buckling load of real imperfect shell structures, thereby promising drastic reduction of the costs of structural engineering experimental tests

Abstract:

Graphene has been widely advertised as the new wonder material that can be produced by exfoliating graphite, using Scotch tape, down to a sheet that is one atom thick .  Because it is a 2-dimensional material, it was expected to revolutionize electronics, but 15 years of exfoliated graphene research has failed to even remotely meet this challenge. Starting in 2000, the Georgia Tech epigraphene electronics group has taken a different approach to graphene-based nanoelectronics, by growing it on single crystals of silicon carbide, using a method that was known for more than 50 years. This form of graphene, called epigraphene, has not only shown a wide variety of important new properties, it also is intrinsically compatible with industrial nanoelectronics fabrication methods.  In this talk I will discuss the historical development of epigraphene starting in the 1880’s and working up to the present day. I will focus on those aspects that sets graphene apart from other electronic materials as well as our recent discoveries of new ballistic edge states and how their quantum mechanical properties might be utilized in a new generation of electronics that utilizes electronic wave interference, like in optics.

Abstract:

Modern machine learning has already proven itself as an indispensable tool incorporating experimental data into existing large-scale computational models of physical systems. However, using machine learning for discovering new physics from experiments is a much harder problem. This is especially true in  biophysics, where traditional theoretical physics intuition based on symmetry and locality is hard to use, and hence automated approaches are likely to be the most impactful. In this talk, I will review a few instances where we were able to discover new physics this way, focusing on behavior of worms and song birds. That is, we were able to make interpretable inferences and generalizations from data, relate them to physical mechanisms, propose new useful experiments, and predict their outcomes, some of which have been confirmed since.