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Condensed Matter / Biophysics Seminars

Spring 2024

Condensed Matter/Biophysics Seminars Mondays at 4:05pm in 2205 NPB


Committee: Yuxuan Wang, Xiao-Xiao Zhang and BingKan Xue


January 8

  Speaker Sangyun Lee, Los Alamos National Lab
  Title Examining symmetry of the superconducting order parameter in UTe2 via specific heat measurements in magnetic field
  Abstract Spin-triplet superconductivity is one of the key platforms with the potential to host Majorana zero modes for topological qubits in quantum computation. I will focus on UTe2, a recently discovered unconventional superconductor where electron Cooper pairs take on a spin-triplet ground state. Here, I will discuss the specific heat C(H,T) of a high-quality single crystal of UTe2 with a single specific heat anomaly at the superconducting transition temperature Tc 2 K and a small zero-field residual Sommerfeld coefficient \gamma0 = C/T (T=0) 10 mJ/mol-K2. Magnetic field is applied up to 12 T along the three principal crystallographic axes of UTe2 to probe the nature of the superconducting state. The evolution of the residual Sommerfeld coefficient as a function of magnetic field, \gamma0 (H), is highly anisotropic and reveals distinct regions. In magnetic field up to 4 T applied along a, b, and c axes, I find \gamma0\alpha_i \sqrt(H), with i=a,b,c, as expected for an unconventional superconductor with nodes (zeros) of the superconducting order parameter on the Fermi surface. A pronounced kink in \gamma0(H), however, is observed at roughly 4 T for field applied along both a and b axes, whereas a smooth change from square-root to linear behavior is observed at 4 T for H||c. These results strongly indicate that a zero-field ground state is stable up to 4 T and undergoes a field-induced evolution above 4 T. ac >aa>ab, indicating that the nodes in the low-field state are predominantly located in the vicinity of the a b plane. The modification of the order parameter is strongest when field is applied in the a b plane, which causes nodes to move away from the direction of the applied field. Both B2u+iB1u and B2u+iAu two-component order parameters can account for my observations. Furthermore, I will introduce my expertise concerning the measurement of physical properties under extreme conditions and highlight the significance of exploring the gap symmetry of materials in such extreme conditions. Also, I will explain to you the techniques used to investigate these gap symmetry, with a specific focus on specific heat measurements at HBT at UF.
  Host Mark Meisel

January 15 (MLK Day)

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January 18 (special date)

  Speaker Guang Yue, University of Illinois Urbana-Champaign
  Title A Study on Quantum Devices and Quantum Materials
  Abstract The Josephson junction device is a powerful tool to study physics. In this presentation the weak link Josephson junction and the topological insulator-based Josephson junction devices will be discussed. First, a superconducting quantum interference device made of weak link Josephson junctions can work directly in a high magnetic field which provides high sensitivity and spacial resolution on magnetic sample measurement. Such a device has been built into a spin resonance measurement setup to study quantum spin for quantum computing purposes. Second, the Majorana bound state physics are studied on the topological insulator-based Josephson junction devices. Evidence of the Majorana bound state is discussed together with methods to utilize such state for topological quantum computing.
  Host Mark Meisel

January 22

  Speaker Zhaoyu Liu, University of Washington, Seattle
  Title Straining Unconventional Superconductors
  Abstract The quantum critical point (QCP) and associated fluctuations play an essential role in understanding the superconducting pairing in the iron-based superconductors. However, the nature of the ground state is still in debate. In this talk, I will focus on the study of the electronic nematic phase and the associated fluctuations by strain techniques. First, I will present a doping evolution of nematic fluctuations in isovalent-doped iron-based superconductors, indicating a nematic QCP at optimal doping. With the application of large uniaxial strain, we can suppress the nematic fluctuations by enhancing the nematic order. Remarkably, the superconductivity is simultaneously suppressed, implying the beneficial role of nematic fluctuations in superconducting pairing. Moreover, we have entirely disrupted the superconducting order from nearly 30 K and revealed, for the first time, an anomalous metal state within a three-dimensional (3D) unconventional superconductor in the dilution temperature range (<100 mK). These observations mark significant leaps in our understanding of the superconducting mechanism in iron-based superconductors. I will also briefly introduce my career path in the development of strain techniques and related research in both 3D and 2D quantum materials.
  Host Mark Meisel

January 23 (4:05PM special seminar)

  Speaker Jiabin Yu (Princeton)
  Title Band geometry and topology in correlated quantum materials
  Abstract Band geometry (or quantum geometry) and band topology describe, respectively, the local and global properties of Bloch electron wavefunctions in quantum materials. These concepts have already triggered a revolution in quantum materials based on single-particle physics, but their significance in interacting systems is much less explored. In this talk, I will discuss two recent advances in this direction for the two major interactions in solids: electron-phonon interaction and electron-electron Coulomb interaction. First, I will explain how quantum geometry contributes crucially to the electron-phonon interaction, potentially offering a new design principle for higher-temperature superconductors. Second, we show that band geometry/topology and band mixing are key to explaining various experimental puzzles centered around fractional Chern insulators (FCIs) recently observed in twisted MoTe2 and graphene-hBN superlattices. FCIs, the zero-field analogs of the fractional quantum Hall effect, are induced by the Coulomb interaction in fractionally filled, (nearly-)flat topological bands, and their discovery heralds the discovery of more exotic topologically ordered phases. These phases, and the diverse computational tools required to predict them, will be discussed.
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January 29 (4:05PM special colloquium)

  Speaker Zachary Nicolaou (University of Washington)
  Title Discovery and design of complex dynamics and pattern formation
  Abstract Complex systems exhibit emergent and collective behavior that defy expectations and amount to more than the sum of their parts. Several classes of systems have been studied in some depth by now, and universal mechanisms have been recognized leading to, for example, synchronization in coupled oscillators, symmetry breaking in pattern-forming systems, and the development of chaos. Recently, data-driven system identification methods have emerged to automate and streamline the discovery of parsimonious and accurate models of real complex systems. This understanding may enable new technological paradigms for computation, information processing, and self-assembly that leverage complexity, much in the way that biological systems have evolved to do. In this talk, I will discuss some recent efforts to design and manipulate emergent behavior in mechanical metamaterials, networks of coupled oscillators, and pattern-forming fluid systems.
  Host BingKan Xue

January 30 (4:05PM special seminar)

  Speaker Zachary Nicolaou (University of Washington)
  Title Spontaneous symmetry breaking in networks of coupled oscillators
  Abstract Complexity in extended systems often emerges through spontaneous symmetry breaking resulting in localized states. Some universal mechanisms for localization have been characterized, such as in the snaking bifurcations of steady states in pattern-forming partial differential equations. While much of this understanding has been targeted at steady states, recent studies have noted complex dynamical localization phenomena in systems of coupled oscillators. I will discuss several recent examples in detail, including examples of chimera states exhibiting a coexistence of coherence and incoherence in symmetric networks of coupled oscillators and gap solitons emerging in the band gap of parametrically driven networks of oscillators. Additionally, I will detail the important role of system symmetry in the continuation and bifurcations of such states as parameters vary.
  Host BingKan Xue

February 1 (3PM special colloquium in NPB 1002)

  Speaker Sumitabha Brahmachari (Rice University)
  Title Physical modeling of chromosomes across species: Mechanistic insights and biological consequences of emergent structural features
  Abstract Chromosomes are long polymers of DNA that are folded into a tiny nucleus by a concerted activity of various proteins. Quantitative understanding of the mechanistic link between protein activity, chromosome architecture, and biological function is nascent but imperative to comprehend how the DNA code governs cellular life. Establishing these links will steer biological research and yield fruitful discoveries in the physics of active polymers. In this talk, I will focus on a physical simulation framework that incorporates genomic data and furnishes mechanistic insights into regulating chromosome structure. I will discuss how this framework has been crucial in rationalizing our observations, linking the activity of specific proteins to conserved architectural features of chromosomes across species spanning the tree of life. We find that the species-wide diversity of structures emerges from a competition between three kinds of generalized forces, where the balance between these forces depends on the relative abundance of specific proteins and is a predictor of the structure. Using this framework, we further explore the elusive link between chromosome structure and crucial biological functionality like segregation or replicated DNA. The developed framework is an essential stride towards a cohesive, physics-based understanding of the chromosome architecture and its implications for cellular life.
  Host BingKan Xue

February 2 (3PM special seminar)

  Speaker Sumitabha Brahmachari (Rice University)
  Title Deciphering the role of the physicochemical properties of DNA in governing biological function
  Abstract Genomic DNA contains the code of cellular life. Understanding the principles regulating transcription of the genetic code is imperative to comprehend biological functions like stress response, disease progression, and cellular differentiation. However, more than just learning the sequence is often required to decode these principles. Appreciating that the chromosomes are folded polymers with well-defined chemical or epigenetic identities and proteins are locally-acting nano-machines that apply forces and torques and catalyze chemical reactions is crucial to unveiling the regulatory principles. In this talk, I will discuss a model for active genic segments that uncovers the role of mechanical constraints in regulating transcription. We propose distinct regimes of DNA twist-mediated coupling between various transcription machinery components that explain novel experimental signatures and make testable predictions. I will conclude with our ongoing efforts toward an integrated picture where an interplay between transcription, epigenetic characteristics, and the three-dimensional architecture of the genome regulate phenotypical characteristics like epigenetic stability and cell fate.
  Host BingKan Xue

February 5

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February 8 (3PM special colloquium in NPB 1002)

  Speaker Gabriel Birzu (Stanford University)
  Title Do bacteria form species? Long term evolution leads to frequent hybridization in a natural microbial community
  Abstract Genetic sequencing of natural bacterial populations often reveals distinct genomic clusters, which are usually interpreted as distinct species. At the same time, recent studies have shown extensive recombination across a wide range of genetic divergences, raising the question of how clusters can be maintained over time. Previous studies have shown that ecological separation can emerge within highly-recombining bacterial populations. However, whether this mechanism can prevent the hybridization and merging of distinct clusters is not known. Here, I show that thermophilic cyanobacteria from the Yellowstone National Park form a rare natural experiment to address this question. By analyzed a large collection of single-cell genomes, I demonstrate that despite their different ecologies, continual hybridization and natural selection have gradually eroded the genetic differences between clusters. These results suggest that ecological barriers cannot by themselves maintain genomic clusters over long evolutionary times and highlight the importance of spatial dynamics for maintaining microbial diversity.
  Host BingKan Xue

February 9 (3PM special seminar)

  Speaker Gabriel Birzu (Stanford University)
  Title Spatial and temporal scales of microbial evolution in theory and nature
  Abstract Microbial evolution occurs across a vast range of spatial and temporal scales. But most of our understanding of evolutionary dynamics comes from studying well-mixed populations over relatively short time scales. Here, I present two approaches that go beyond these constraints. In the first part, I show how fine-scale patterns of genetic diversity within a natural bacterial population can reveal surprising quantitative insights into their evolutionary history. By combining information from geological records with genetic sequencing analysis, I find that on time scales of ~10^4 years barriers between species are gradually eroded. This very slow hybridization process occurs over an area of ~3500 km^2, in which the population is effectively well-mixed. These results suggest that effective parameters describing microbial evolution on long time scales may be very different from the parameters measured in experiments, which poses exciting new challenges for theory. In the second part, I present recent theoretical work on describing the genealogical structure of expanding populations. I show that genealogical trees across a wide range of models fall into three distinct universality classes, characterized by a single dynamical variable proportional to the expansion velocity. This surprisingly simple result provides a robust mechanism that can lead to genealogies similar to those from populations under strong selection.
  Host BingKan Xue

February 12 (4:05PM special colloquium)

  Speaker Ugur Cetiner (Harvard Medical School)
  Title Insights from life: a physicist's perspective
  Abstract Life is inherently away from thermodynamic equilibrium. However, the analysis of non-equilibrium steady states has been hampered by combinatorial complexity. In the midst of this complexity, there are still interesting thermodynamic structures. I am going to exploit a graph-theoretic representation of Markov processes to reformulate non-equilibrium steady-state probabilities in a way that makes their descriptions independent of system size and gives them thermodynamic meaning. I am going to conclude by showing how analyzing the non-equilibrium physics of living systems can provide new physics insights.
  Host BingKan Xue

February 13 (4:05PM special seminar)

  Speaker Ugur Cetiner (Harvard Medical School)
  Title The role of energy in cellular information processing
  Abstract The development of new experimental methods in biology and the ability to probe life at the nanoscale have been redrawing the intellectual landscape of non-equilibrium physics. I am going to discuss how energy expenditure can be used to gain new functional capabilities, especially in the context of biological error correction. Also, I am going to discuss new, energy-induced bounds on cellular information processing and suggest experiments to test these ideas. These bounds are universal, in the sense of holding for any Markov process, irrespective of underlying parameter sets, and they are valid even if the underlying system operates far from thermodynamic equilibrium. Our results suggest how we can “follow the energy” to unravel the functional logic of non-equilibrium systems in physics and biology.
  Host BingKan Xue

February 19

  Speaker Julius de Rojas, Oklahoma State
  Title Current(less) Trends in Spintronics: Magnetoionics & Magnonics for Energy Efficient Devices
  Abstract Fundamental hurdles, including power constraints and manufacturing limitations, have left conventional computing hardware struggling to maintain energy efficiency as dimensions continue to shrink, leading to several approaches to low-energy data storage and processing. In this talk, I will present magneto-ionics and magnonics, two emerging branches of spintronics which offer potential as low-energy platforms for data storage and processing. I will then present our study of magneto-ionics in oxygen-based and nitrogen-based systems as a low-energy means to toggle magnetization states. I will focus on the structural ion approach, in which the mobile ions are already present in the target material and discuss its potential advantages and challenges. I will then conclude with our investigation into the static and dynamic behavior of pseudo-3D trilayer square artificial spin ice structures for magnonic applications, in which a nonmagnetic copper layer of varying thick-ness is inserted between Permalloy (Ni81Fe19) layers. We show that the copper thickness enables interlayer coupling between layers to be finely controlled, leading to bespoke magnetization states and resonance spectra tuning, a potentially programmable degree of freedom for magnonic and microwave devices.
  Host Dominique Laroche

February 21 (Special Seminar) 4:00pm in NPB 2205

  Speaker Wei Chen, Pontifical Catholic University
  Title Seeing topological charge by naked eyes
  Abstract We uncover that the opacity of graphene, which is known to be given by the fine structure constant, is actually protected by the topological charge of the Dirac point owing to a correspondence between quantum metric and topological charge. As a result, one can literally see the topological charge by naked eyes, and moreover it implies that the fine-structure constant is topologically protected. We further predict that the opacity of 3D topological insulators in the infrared region is also given by the fine structure constant, implying that one can see the topological surface states through an infrared lens. These optical observation of topological order can be generalized to atomic scale measurements through utilizing the concept of topological markers, which allow the effect of disorder to be quantified. Based on these markers, we will present an analytical proof for the conditions under which the topological invariant remains quantized in the presence of disorder, which reminisces Anderson's theorem in disordered superconductors.
  Host Peter Hirschfeld

February 26

  Speaker Rudi Hackl (IFW Dresden)
  Title Raman Study of Electronic Interactions in Kagome Lattice Systems
  Abstract Quasi two-dimensional systems with some of the atoms sitting on a kagome network of alternating hexagons and triangles display a variety of intriguing properties such as exotic magnetic ordering phenomena, quantum spin liquid phases, density wave order or superconductivity. Practically all of these phenomena are related to the electronic band structure hosting Dirac points, Weyl nodes and flat bands as result of the specific arrangement of atoms. It remains a challenge to properly pin down the interactions which are responsible for the ordering phenomena and the various ground states. In Fe3Sn2, a ferromagnet having a Curie temperature TC of 670 K, the spins reorient from parallel to perpendicular to the kagome plane below approximately 150 K. CsV3Sb5 exhibits a charge density (CDW) wave below 94 K and becomes superconducting below 2.5 K. It is still under debate in which direction the Vanadium atoms move below TCDW. In Co3Sn2S2, the Co spins form a nearly frustrated antiferromagnet below TC = 177 K with a very weak ferromagnetic moment perpendicular to the plane. Ferromagnetism becomes stronger at low temperature having a moment of approximately 0.3 uB per Co parallel to the c-direction. We used polarization-resolved Raman spectroscopy to clarify the origin of some of these phenomena and to shed light on the underlying interactions. We find phonon anomalies at the ordering temperatures of CsV3Sb5 and Co3Sn2S2 and in the range where the spins in Fe3Sn2 reorient. In both CsV3Sb5 and Co3Sn2S2, one A1g phonon exhibits a significant asymmetry indicating strong electron phonon coupling. In CsV3Sb5, also the A1g CDW amplitude mode is asymmetric. In both CsV3Sb5 and Co3Sn2S2, the electronic intensity is redistributed indicating a large CDW gap and, respectively, a splitting of the conduction bands in spin up and spin down bands. The simulations using density-functional theory (DFT) reproduce the observed spectral changes. For CsV3Sb5, the simulations show that both energy considerations and spectroscopy support the tri-hexagonal rather than the Star of David distortion. The large electronic gap, the enhanced anharmonic phonon-phonon coupling, and the Fano shape of the amplitude mode are more supportive of a strong-coupling phonon-driven CDW transition than of a Fermi surface instability or an exotic mechanism.
  Host Chunjing Jia

March 4

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March 18 (POSTPONED)

  Speaker Orit Peleg, University of Colorado Boulder
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  Host BingKan Xue

March 25

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April 1

  Speaker Zhen Bi, PSU
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April 8

  Speaker Luca Delacretaz, U Chicago
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  Host Yuxuan Wang


April 15

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April 22

  Speaker Saurabh Maiti (Concordia University)
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  Host Hirschfeld and Maslov


Condensed Matter / Biophysics Seminars

Fall 2023

Condensed Matter/Biophysics Seminars Mondays at 4:05pm in 2205 NPB


Committee: Yuxuan Wang, Xiao-Xiao Zhang and BingKan Xue


August 28

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September 4

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September 11

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September 18

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September 25

  Speaker Youngmin Park, UF Math
  Title High-Order Accuracy Computation of Coupling Functions for Strongly Coupled Oscillators
  Abstract We develop a general framework for identifying phase reduced equations for finite populations of coupled oscillators that is valid far beyond the weak coupling approximation. This strategy represents a general extension of the theory from [Wilson and Ermentrout, Phys. Rev. Lett 123, 164101 (2019)] and yields coupling functions that are valid to higher-order accuracy in the coupling strength for arbitrary types of coupling (e.g., diffusive, gap-junction, chemical synaptic). These coupling functions can be used to understand the behavior of potentially high-dimensional, nonlinear oscillators in terms of their phase differences. The proposed formulation accurately replicates nonlinear bifurcations that emerge as the coupling strength increases and is valid in regimes well beyond those that can be considered using classic weak coupling assumptions. We demonstrate the performance of our approach through two examples. First, we use diffusively coupled complex Ginzburg-Landau (CGL) models and demonstrate that our theory accurately predicts bifurcations far beyond the range of existing coupling theory. Second, we use a realistic, synaptically coupled, conductance-based models of a thalamic neuron and show that our theory correctly predicts asymptotic phase differences for non-weak synaptic coupling. In both examples, our theory accurately captures model behaviors that weak coupling theories cannot.
  Host Juan Guan, Bingkan Xue, and Yoonseok Lee


October 2

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October 9

  Speaker Nicolas Silva, UF Maglab HighB/T
  Title Spherical Neutron Polarimetry at Oakridge National Laboratory
  Abstract Spherical Neutron Polarimetry (SNP) analyzes complex magnetic structures through distinguishing contributions from nuclear-magnetic interference and chiral structure in addition to nuclear magnetic scattering separation. This analysis is achieved through determining all components in the polarization transfer process. The SNP device consists of three units: incoming/outgoing neutron polarization, sample environment and a zero-field chamber. The incoming/outgoing neutron polarization regions use high- superconducting YBCO films and mu-metal to achieve full control of neutron polarization. The sample environment is an orange cryostat with a customized tail piece placed into the zero-field chamber. The device has been tested at the University of Missouri research reactor (MURR), HYSPEC, HB-1, and CG-4B. The testing demonstrates that the device functions as intended but can still be improved. Further testing explores improvements to the device via magnetic shielding and polarization control. These efforts are to create the optimal device to be included into the user program at ORNL.
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October 16

  Speaker Denis Karaiskaj, University of South Florida
  Title Coherent and magneto-optical Kerr spectroscopy at extremely high magnetic fields
  Abstract Magnetic field- and polarization-dependent measurements on bright and dark excitons in monolayer MoSe2 and WSe2 combined with time-dependent density functional theory calculations reveal intriguing phenomena. Magnetic fields up to 25 T parallel to the WSe2 plane lead to a partial brightening of the energetically lower lying exciton, leading to an increase of the dephasing time. Using a broadband femtosecond pulse excitation, the bright and partially allowed excitonic state can be excited simultaneously, resulting in coherent quantum beating between these states. The magnetic fields perpendicular to the WSe2 plane energetically shift the bright and dark excitons relative to each other, resulting in the hybridization of the states at the K and K valleys. Our experimental results are well captured by time-dependent density functional theory calculations. These observations show that magnetic fields can be used to control the coherent dephasing and coupling of the optical excitations in atomically thin semiconductors.

In the presence of magnetic fields perpendicular to the MoSe2 plane the coherence at negative and positive time delays is dominated by intervalley biexcitons. We demonstrate that magnetic fields can serve as a control to enhance the biexciton formation and help search for more exotic states of matter, including the creation of multiple exciton complexes and excitonic condensates. Finally, static and magneto-optical Kerr effect measurements are used to investigate a host of kagome lattice helimagnets and topological magnetic materials. These measurements are performed at extremely high magnetic fields and as a function of temperature enabling us to investigate their full phase diagram.

N. P. Pradhan et al., Nanoscale 15, 2667 (2023)
Liu et al., Physical Review B 106, 035103 (2022)
V. Mapara et al., Nano Letters 22, 1680 (2022)
J. Paul et al., Rev. Sci. Instrum. 90, 063901 (2019)
P. Das et al., Nanoscale 12, 22904 (2020)
C. E. Stevens et al., Nature Communications 9, 3720 (2018)
C. E. Stevens et al., Optica 5, 749 (2018)
J. Paul, et al., Phys. Rev. B 95, 245314 (2017)
C. E. Stevens, et al., Solid State Commun. 266, 30 (2017)
P. Dey, et al., Phys. Rev. Lett. 116, 127402 (2016)
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October 23

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October 30 (POSTPONED)

  Speaker Orit Peleg, University of Colorado Boulder
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November 6

  Speaker Yingying Wu, UF ECE
  Title Towards Ultralow-Power and Scalable 2D Topological Spintronics Using Quantum Devices
  Abstract The current electronics industry is facing challenges both from the fundamental physics limit of silicon on the small scale, and the new demand for big-data applications on the large scale. Spintronics, utilizing spin degree of freedom, is a promising for future beyond-CMOS devices and systems, thanks to their low power consumption, nonvolatility, and easy 3D integration. The emerging 2D magnets can preserve single-phase magnetism even in monolayer (~0.8 nm) limits, and thus they are promising to further scale down devices. They have a sharp interface and atomically thin nature, promising for designer quantum devices and more functionalities (e.g. stacking order, twist angle, thickness, and voltage control).

In this talk, I will discuss 2D spintronics with quantum devices on skyrmions and antiferromagnets, and their potential applications. I will begin by presenting my observations of real-space topological spin textures - magnetic skyrmions. This work represents the first report of skyrmion lattice imaging in 2D layered magnets. Building on this, I will present my findings on the vertical imprinting of skyrmions onto neighboring layers in a 2D ferromagnet/2D ferromagnet system, demonstrating new functionality for skyrmion-based spintronics. I will then discuss the exchange coupling and voltage controlled 2D antiferromagnetism in devices, a step towards ultralow-power and ultrafast spintronics. In addition, future work on quantum devices is motivated that would focus on energy-efficient control in magnetism, for neuromorphic and quantum computing.
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November 13

  Speaker Gordon Berman, Emory University
  Title Measuring the hidden dynamics of animal behavior
  Abstract Unlike most physical systems, animal behavior consists of an intricate hierarchy of dynamics, from brief muscle twitches to stereotyped behaviors to longer-lived states like hunger, aggression, and parenting to are difficult to parse apart through typical analytical means. How does an animal bridge these timescales to create complex sequences of actions? The approach that most researchers take when studying sequences of behaviors tends to be strictly probabilistic, observing how discrete states transition in a largely memoryless, Markovian fashion. In this talk, I will describe a different approach: fitting dynamical models to long behavioral sequences from fruit flies and rodents. We show that these models replicate many summary statistics of the underlying behavioral sequence data and that their fixed points have a geometry that mirrors the geometry of the animals' behavioral repertoires. In addition, we show that the long timescales generated by this model are best explained by a hierarchy of interacting dynamical subsystems. These results can be used to make predictions about the underlying "hidden" physiological states governing behavior and how behaviors may evolve.
  Host BingKan Xue

November 20

  Speaker Ryan Need (they/them) , UF Materials Science and Engineering
  Title Ordered States in Disordered Magnets and Superconductors
  Abstract The interplay order and disorder in condensed matter has intrigued scientists for decades and continues to be an active area of research today. Recently, a new approach to synthesizing materials with extreme amounts of point-defect disorder has been developed and successfully applied to both metal alloys and ceramics. This process is known as "entropy-stabilized" or "entropy-enhanced" alloying and works by placing 4-5 elements on a lattice site that typically only hosts 1 element. This increases the number of possible microstates and configurational entropy of the material, which in turn drives the free energy negative and stabilizes homogeneously-mixed, single-phase materials with large disorder.

In this talk, I will describe two recent studies where my group has used entropy-enhanced alloying to study the effects of disorder localized to specific lattice sites on the stability of ordered phases like magnetism and superconductivity. In the first study, we entropy-alloyed different sites in the perovskite (ABO3) crystal structure and measured the system's ability to form long-range magnetic structures. Alloying on the perovskite B-site causes the magnetic structure to fragment into a mixed phase microstructure, whereas alloying on the A-site resulted in only minor perturbations to the expected long-range magnetic structure. In the second study, we applied entropy-alloying to the high-temperature cuprate superconductor, YBa2Cu3O7-x. Remarkably, our results show almost no suppression of the electron pairing interaction strength as measured by the transition temperature, despite large amounts of spin disorder added to the system. Taken together, these studies highlight how electronic and magnetic order in materials can be sensitive to some types of disorder while robust to others, and demonstrate how entropy-alloyed materials provide a highly versatile platform for re-examining order-disorder phenomena in condensed matter.
  Host Mark Meisel (he/him)

November 27

  Speaker Ryan Need (they/them) , UF Materials Science and Engineering
  Title MagLab High B/T Facility: review of year one and future plans
  Abstract The National High Magnetic Field Laboratory (MagLab) High B/T Facility (HBT) in the Department of Physics is nearing the end of the first year of the 5-year (2023-2027) NSF grant [1]. The purpose of this talk is to provide a review of recent work, an update on present activities, and a projection of future directions. In addition, a few moments will be devoted to discussing the visits of the two finalists for the MagLab Director position [2]. As part of the discussion about HBT activities and operations, comments from the 2023 annual reports from the MagLab External Advisory Committee [3] and Users Committee [4] will be presented as a springboard to addressing the issue of future HBT faculty engagement and leadership. The significance of MagLab connectivity to the Department of Physics, experiment and theory, is an underlying theme of the presentation.
  Host Mark Meisel (he/him)

December 4

  Speaker Arthur Porto, UF Florida Museum Curator of AI
  Title Constraints in the evolution of form of an unique group of marine invertebrates
  Abstract Marine invertebrates are an excellent model system for the study of long-term morphological evolution, largely in part due to their extensive fossil record and complex skeletal features. As a consequence, this group should be at the forefront of current discussions on the nature of evolvability, such as: Why are rates of evolution so different between short- and long-term studies? What factors make certain species exceptional evolvers? What constraining mechanisms are shaping the evolutionary diversification of certain lineages? By applying computer vision-based techniques to scanning electron microscopy images encompassing multiple lineages of marine invertebrates, including the stratigraphically rich Steginoporella magnifica, I will discuss the critical role of functional constraints in shaping the course of morphological evolution in this group.
  Host BingKan Xue

December 11

  Speaker Ting Ge, University of South Carolina
  Title Mechanics of Non-Concatenated Ring Polymers: Effects of Topology Revealed by Molecular Simulations
  Abstract Few aspects are as prevalent and vital as topology in polymer mechanics, which provides an essential foundation for versatile functions of polymeric materials. Recent advances in chemistry have enabled the precise synthesis of non-concatenated ring polymers with distinctive topology. While many aspects of the statics and dynamics of ring polymers have been elucidated in the past several decades, the structure-property relationship has not been completely established for ring polymer mechanics. Using molecular simulations with perfect control of polymer topology, we make elastomers and thermoplastics out of non-concatenated ring polymers and investigate their mechanical properties during large deformation and failure. The simulations reveal that the elastomers made of cross-linked ring polymers are significantly more stretchable than cross-linked linear polymers [1]. Compared to linear polymers, the entanglements between ring polymers do not act as effective cross-links. As a result, the stretchability of cross-linked ring polymers is determined by the maximum extension of polymer strands between cross-links rather than between trapped entanglements, which is the case in cross-linked linear polymers. The simulations also reveal that the thermoplastics made of ring polymers fail through crazing as their linear counterparts under tensile loading [2]. The stable craze formation indicates the existence of an entanglement network in glassy ring polymers. Nevertheless, the entanglement network consists of only a fraction of the topological constraints that determine the conformations of ring polymers. Both the structural features of the ring polymer craze and the drawing stress during the craze formation are related to the underlying entanglement network. Besides the simulations, molecular theories have been developed to delineate the mechanical behaviors of ring elastomers and ring thermoplastics. The studies demonstrate the use of ring polymers as a transformative pathway to tailor polymer mechanics, propelling a new paradigm of topological polymer physics entering materials science.
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