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The properties of a material are often thought to be determined primarily by the elements from which it is made. But what happens when the geometry of a crystal lattice itself becomes a source of new quantum phenomena? In this talk, I will explore this question through the physics of kagome metals—materials whose atoms form a network of corner-sharing triangles. The kagome lattice provides a remarkable example of how geometry can reshape the electronic landscape of a metal. Quantum interference between electronic pathways produces nearly flat electronic bands, while the same lattice can host Dirac-like band crossings and van Hove singularities, where the density of electronic states becomes strongly enhanced. These features can dramatically amplify the effects of interactions between electrons, creating an unusually rich environment for collective quantum phenomena. Kagome materials have consequently emerged as a platform for studying charge-density waves, magnetism, unconventional superconductivity, nematicity, anomalous Hall responses, and other forms of intertwined and potentially topological order. I will discuss how these ideas emerge from the electronic structure and how they manifest experimentally in real materials. In particular, I will highlight recent work from my group using the experimental technique of angle-resolved photoemission spectroscopy (ARPES) to directly visualize the electronic states of several kagome metals and to follow their evolution across the various phase transitions. These experiments reveal an intimate connection between the underlying band structure and the collective behavior of the electrons, while also highlighting the ways in which real materials can depart from simple theoretical pictures.
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Selected Publications
We report on the observation and measurement of astrometry, photometry, morphology, and activity of the interstellar object 3I/ATLAS, also designated C/2025 N1 (ATLAS) with the NSF-DOE Vera C. Rubin Observatory. Comet 3I/ATLAS, the third known interstellar object, was discovered on UT 2025 July 1. Rubin Observatory had coincidentally collected images of the object’s region of the sky during routine commissioning. Facilitated by Rubin’s high resolution and large aperture, we successfully recovered object detections from Rubin observations spanning UT 2025 June 21 (10 days before discovery, when 3I/ATLAS was 4.5 au from the Sun) through the date of discovery, and we acquired additional images through UT 2025 July 20 as part of commissioning. We measure on-sky locations of 3I/ATLAS in Rubin ugrizy bands, with a typical precision of ∼70 mas, and briefly describe the reason this is coarser than our measured static source astrometric precision of ∼3 mas in Rubin images. We measure grizy magnitudes of 3I/ATLAS photometry at ∼0.01 mag precision, detecting no short-term photometric variability above 0.01 mag. We derive an estimated near-nucleus dust-to-nucleus scattering cross-sectional ratio of η ≳ 13 on UT 2025 July 2 based on Rubin photometry and an upper limit nucleus size computed from Hubble Space Telescope observations. We find Rubin colors of g − r = (0.657 ± 0.013) mag, r − i = (0.235 ± 0.018) mag, i − z = (0.147 ± 0.042) mag, and z − y = (0.047 ± 0.052) mag. These data represent the earliest observations of this object by a large (≳8 m class) telescope and illustrate the type of measurements (and discoveries) Rubin’s Legacy Survey of Space and Time will provide after it begins in early 2026.
Artificial intelligence foundation models are increasingly deployed for prostate cancer Gleason grading, where GP3/GP4 distinction directly impacts treatment decisions (active surveillance vs. intervention). However, these models may achieve high validation accuracy by learning specimen-specific artifacts rather than generalizable biological features, limiting real-world clinical utility. We introduce PANDA-PLUS-Bench, a curated benchmark dataset derived from expertly annotated prostate biopsies designed specifically to quantify this failure mode. The benchmark comprises nine carefully selected whole slide images from nine unique patients containing diverse Gleason patterns, with non-overlapping tissue patches extracted at both 512 × 512 and 224 × 224-pixel resolutions across eight augmentation conditions. Using this benchmark, we evaluate seven foundation models (Virchow, Virchow2, UNI, UNI2, Phikon, Phikon-v2, and HistoEncoder) on their ability to separate biological signals from slide-level confounders. Our results reveal substantial variation in robustness across models: the Virchow models achieved the lowest slide-level encoding among large-scale models (slide ID accuracy: 80.7–81.0%), yet Virchow2 exhibited the lowest cross-slide accuracy (47.2%). HistoEncoder, trained specifically on prostate tissue, demonstrated the highest cross-slide accuracy (59.7%) and the strongest slide-level encoding (slide ID accuracy: 90.3%), suggesting tissue-specific training may enhance both biological feature capture and slide-specific signatures. All models exhibited measurable within-slide vs. cross-slide accuracy gaps, though the magnitude varied from 19.9 percentage points (HistoEncoder) to 26.9 percentage points (Phikon). We provide an open-source Google Colab notebook enabling researchers to evaluate additional foundation models against our benchmark using standardized metrics. PANDA-PLUS-Bench addresses a critical gap in foundation model evaluation by providing a purpose-built resource for robustness assessment in the clinically important context of Gleason grading.
Pyrochlore magnets of the form 𝑅2𝐵2O7, in which rare-earth ions on the 𝑅 site form a three-dimensional network of corner-sharing tetrahedra, provide a canonical setting for geometrical frustration. Ho-based pyrochlores host a dipolar spin-ice ground state, characterized by Ising moments constrained by the ice rules and elementary excitations analogous to magnetic monopoles. Here we examine how controlled chemical disorder influences this state by introducing site mixing on the nonmagnetic 𝐵 site in two compounds. Ho2GaSbO7 contains only Ga3+/Sb5+ charge disorder, whereas Ho2ScSbO7 exhibits both charge and substantial size disorder arising from the large ionic-radius mismatch between Sc3+ and Sb5+. Although both materials retain the pyrochlore structure, neutron-scattering measurements reveal a reduced correlation length for the 𝑅/𝐵-site cation ordering and enhanced local structural distortions in Ho2ScSbO7. Despite these structural differences, bulk thermodynamic measurements and magnetic diffuse scattering demonstrate that both systems exhibit the defining signatures of a dipolar spin-ice state. Low-energy inelastic neutron spectroscopy further uncovers broad magnetic excitations that develop within the dipolar spin-ice regime, a feature absent in pristine Ho pyrochlores and indicative of disorder-induced splitting of the non-Kramers ground-state doublet. Together, these results show that controlled disorder generates tunable transverse-field-driven quantum fluctuations in Ho-based pyrochlores, although the dipolar spin-ice state is remarkably robust to this disorder.
Borna disease virus 1 (BoDV-1) is a non-segmented negative-strand (NNS) RNA virus that uniquely replicates in the nucleus of mammalian host cells, in contrast to most NNS RNA viruses that replicate in the cytoplasm. The mechanisms underlying nuclear replication of BoDV-1 and related bornaviruses with their RNA-dependent RNA polymerase (RdRp) complexes remain poorly understood. Here, we report the 2.8 Å cryo-EM structure of the BoDV-1 RdRp complex, comprising the large (L) protein and tetrameric phosphoprotein (P). The L protein features an N-terminal superdomain containing the RdRp and GDP polyribonucleotidyltransferase (PRNTase, mRNA-capping enzyme) domains, along with three C-terminal appendages, including a methyltransferase-like domain. The RdRp initiates de novo RNA synthesis internally at the genomic promoter, producing 5′-triphosphorylated transcripts corresponding to the 5′ end of the anti-genome. P interacts with the fingers RdRp subdomain of L. Structure-guided mutagenesis shows that the residues involved in the L–P interaction are essential for efficient transcription initiation and, consequently, for viral gene expression. A flexible loop within the PRNTase domain, analogous to the rhabdovirus priming-capping loop, appears critical for transcription initiation. These findings provide the structural and functional insights into the BoDV-1 RdRp and support a shared evolutionary origin between nuclear and cytoplasmic NNS RNA viruses.
Glycine receptors (GlyRs), pentameric ligand-gated ion channels (pLGICs), mediate sensory and motor functions. GlyR functional states are well characterized; however, structural details of transitions between states remain undefined. Here, we determined cryo–electron microscopy structures of GlyRα1β (with gephyrin E-domain) at varying concentrations of ivermectin, a transmembrane domain (TMD) allosteric agonist, and at saturating concentrations of strychnine, a competitive antagonist at the extracellular domain (ECD). Electrophysiology shows that ivermectin activates GlyR even with strychnine present. Structures with both ligands reveal intermediate states featuring a desensitized TMD and an ECD between closed and desensitized conformations, providing insights into domain cooperativity and ligand efficacy. Molecular dynamics simulations show how ivermectin affects strychnine dynamics. These data support a model where ivermectin activates GlyRs through a concerted and near-symmetric TMD mechanism, whereas allosteric ECD motions are graded and spatially heterogeneous. These findings reveal unanticipated features of GlyR gating and establish principles of allosteric modulation applicable to pLGICs.
Glycine receptors (GlyRs) mediate inhibitory neurotransmission in the central nervous system. The GlyRα2 subtype contributes to critical neural circuitry in early neurodevelopment and is also found in adults. GlyRα2 dysfunctions are implicated in neurodevelopmental disorders, including autism, epilepsy, and cognitive delays. GlyRα2 functional properties and pharmacology are distinct from GlyRα1, but the structural basis for these differences remains poorly defined. Here, we report cryo-electron microscopy structures of full-length, human GlyRα2 reconstituted in peptidiscs captured in multiple conformational states. In addition to symmetric resting and desensitized states, we resolved an asymmetric open state, previously observed only in heteromeric GlyRs. This suggests that asymmetry is intrinsic to GlyRα2, independent of β-subunit incorporation. Furthermore, we identified distinct conformations of GlyRα2 with the pore-blocker picrotoxin, providing new insights into allosteric interactions. These findings uncover the structural basis of GlyRα2 function, providing a foundation for understanding its role in development and in GlyRα2-associated disorders.