Condensed Matter / Biophysics Seminars |
Spring 2023 |
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Condensed Matter/Biophysics Seminars
Mondays at 4:05pm in 2205 NPB
Committee: Yuxuan Wang, Xiao-Xiao Zhang and Purushottam Dixit |
January 9 |
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| Speaker | Xiaomeng Liu (Princeton University) | |
| Title | VdW heterostructures: a new route to designing quantum matters | |
| Abstract | In quantum materials, fascinating phenomena arise from trillions of interacting electrons, such as superconductivity and non-abelian anyons. Harnessing these quantum properties is the key to future quantum technologies. Over the past decade, the development of two-dimensional (2D) materials and their heterostructures has revolutionized the quantum material field. Mechanically assembled layer-by-layer and held together by the van der Waals (vdW) force, vdW heterostructures place no constraint on constituent layers' chemical compositions and lattice parameters. The versatility and tunability of these 2D platforms have enabled a wide range of quantum states of matter, spanning various correlated and topological orders. In this talk, I will feature two examples of designing quantum matters with vdW heterostructures. The first example exploits Coulomb interactions across separate atomic layers to create a novel superfluid--the exciton condensate. By varying the pairing strength, the nature of this condensate is tuned from the strongly-coupled BEC regime to the weakly-coupled BCS regime, realizing the long-sought BEC-BCS crossover of fermion condensates. In the second example, two 2D layers (Bernal bilayer graphene) are placed directly on each other but with a twist. The beating between the two atomic lattices gives rise to a moiré pattern that defines a new length scale and reforms the energy structure. With electric control, highly-degenerate electron bands are achieved, leading to strong electron correlation and spontaneous symmetry breaking. More broadly, the rich interplays across atomic interfaces in vdW heterostructures provide gateways to major themes in condensed matter physics and new quantum devices, both of which will be the focus of my future lab. I will also briefly share my recent works and envisioned efforts to apply local probe techniques to reveal hidden quantum properties in 2D platforms. |
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January 16 |
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January 23 |
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| Speaker | Rahul Nandkishore (CU-Boulder) | |
| Title | Ultrafast interrogation of quantum materials | |
| Abstract | Developments in non-linear ultrafast spectroscopy allow us to probe many body quantum dynamics in the solid state, yielding novel insights into quantum materials. I highlight key advances in this emerging field, including the application of non-linear spectroscopic techniques to resolve longstanding open problems in silicon, and proposals to use such techniques for diagnosis and characterization of fractionalized excitations in quantum spin liquids and beyond. Refs: Observation of a marginal Fermi glass. Fahad Mahmood, Dipanjan Chaudhuri, Sarang Gopalakrishnan, Rahul Nandkishore, N. P. Armitage, Nature Physics 17, 627-631 (2021). Spectroscopic fingerprints of gapped quantum spin liquids, both conventional and fractonic. Rahul M. Nandkishore, Wonjune Choi and Yong-Baek Kim, Phys. Rev. Research 3, 013254 (2021) Extracting spinon self-energies from two-dimensional coherent spectroscopy. Oliver Hart and Rahul Nandkishore, arXiv: 2208.12817 |
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| Host | Yuxuan Wang | |
January 30 |
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February 6 |
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February 13 |
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February 20 |
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February 27 |
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| Speaker | Prof Na Hyun Jo (University of Michigan) | |
| Title | Manipulation of Quantum Materials Through Strain | |
| Abstract | A major question in basic physical research is how to understand the collective behavior of interacting quantum objects that cannot be treated as non-interacting particles. Many-body interactions in complex quantum materials are an ideal platform because the interactions cause fascinating phenomena such as high-temperature superconductivity, exotic magnetic systems, correlated topological materials, and many others. In addition, four fundamental degrees of freedom, lattice, charge, orbital, and spin, provide strong tunability on the exotic properties, which allow enhancing our understanding of interacting quantum objects. Strain is a novel way of approaching the four parameters without extrinsic perturbations. In this talk, a modern uniaxial stress device for electrical transport and angle-resolved photoemission spectroscopy (ARPES) will be introduced. With the device, we studied the fundamental response of electronic structure as a function of strain, which contains key information about the intrinsic physical properties of quantum materials. We will also discuss our recent findings of stain tuning of topological states | |
| Host | Yoon Lee | |
March 6 |
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March 20 |
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| Speaker | Yiming Wu (Stanford) | |
| Title | Mechanism of pair-density-wave from electron repulsion | |
| Abstract | While uniform superconductivity has been observed in many materials, that with finite center-of-mass momentum pairing, also known as pair-density-wave, stays rare in nature. In this talk I will introduce both weak and intermediate coupling theories to explain the underlying mechanism for PDWs from electron repulsion. The weak coupling theory generally involves Fermi surface nesting in the particle-particle channel, while the intermediate coupling theory requires local suppression and is a threshold phenomenon. Typical examples such as moire bilayer systems and Kagome metals will be discussed. | |
| Host | Yuxuan Wang | |
March 27 |
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April 3 |
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| Speaker | BingKan Xue (UF Physics) | |
| Title | Physical limits of biological adaptation, interaction, and perception due to individual variations | |
| Abstract | The field of biological physics has grown from applying physics methods to biological systems to searching for new principles in biological systems that expand the scope of physics. One such principle that uniquely characterizes biological systems is the fact that individuals in any biological population are so diverse in their traits that they cannot be treated as "identical particles", as often done in physical modeling. Such individual variation has important consequences on the ecology and evolution of biological species. In this talk, I will present work in my group that has looked at several examples of biological processes where individual variations result in various constraints on the extent to which species can adapt to changing environments, persist under species interactions, and perceive patterns from signals. I will first discuss the benefit of population diversity for adaptation in varying environments and show that the benefit can be increased by organisms utilizing external and internal sources of information. Then I will consider predatory interactions between species and show that trait variation within species can lead to unexpected outcomes, such as the predator being able to promote the abundance of the prey rather than reducing it. Finally, I will mention our latest work on mimicry and color perception, where individual variation of display patterns may redefine the criterion of resemblance and explain the "imperfect mimicry problem" in evolution. | |
| Host | Xiaoguang Zhang | |
April 10 |
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| Speaker | Yakov Gindikin (University of Minnesota) | |
| Title | Pair spin-orbit interaction in low-dimensional electron systems' | |
| Abstract | The work is devoted to the effects of the pair spin-orbit interaction (PSOI) in Rashba materials. The PSOI is the electron-electron interaction component that depends on the spin and momentum of the electrons. Being produced by the Coulomb fields of interacting electrons, it exists already in vacuum, but becomes orders of magnitude larger in materials with the giant Rashba effect. The main nontrivial feature of the PSOI is that it is attractive for electrons in certain spin configurations tied to their momentum and competes with the Coulomb repulsion of the electrons. Under certain conditions attainable in modern low-dimensional structures the PSOI prevails. The resulting attraction between the electrons leads to the formation of the bound electron pairs, the binding energy of which can be controlled by electrical means. In many-electron systems the PSOI results in the instabilities of the uniform ground state with respect to the density fluctuations, which develop on different spatial scales, depending on the geometry of the electric fields that produce the PSOI. If the PSOI is not too strong the electronic system is stable, but its collective excitations reveal the highly unusual spin-charge structure and spectrum, which manifest themselves in the frequency dependence of the dynamic conductivity. | |
| Host | Dmitrii Maslov | |
Condensed Matter / Biophysics Seminars |
Fall 2022 |
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Condensed Matter/Biophysics Seminars
Mondays at 4:05pm in 2205 NPB
Committee: Yuxuan Wang, Xiao-Xiao Zhang and Purushottam Dixit |
August 29 |
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September 5 |
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September 12 |
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September 19 |
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September 26 |
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October 3 |
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| Speaker | Chunjing Jia (UF Physics) | |
| Title | Searching for excitonic insulators in low-dimensional systems | |
| Abstract | The excitonic insulator is a long-conjectured quantum phase that could occur in narrow-gap semiconductors or semimetals. In these systems, electron-hole pairs (excitons) can be created spontaneously and Bose condense into a collective state at low temperatures. Many of the EI candidates are also known to exhibit a structural transition across the putative EI phase transition, complicating the unambiguous identification of EI in these materials. In my talk, I am going to discuss two studies on the investigation of excitonic insulator candidates. One is about monolayer 1T-ZrTe2, a sister compound of excitonic insulator candidate 1T-TiSe2 in the two-dimensional limit. With a combination of theoretical calculation and angle-resolved photoemission spectroscopy measurement, exciton gas phase was observed above transition temperature Tc, suggesting a BEC type of excitonic insulator. [1] The second study is about Ta2NiSe5, a quasi-one-dimensional material. Combination of resonant inelastic x-ray scattering measurement and theoretical calculations show that gap opening in Ta2NiSe5 below transition temperature Tc is likely driven by the structural transition, although a minor contribution from excitonic insulator state may not be excluded. [2]
[1] Arxiv: 2201.11592 (2022) [2] Phys. Rev. B. 103, 235150 (2021) |
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October 10 |
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| Speaker | Andrey Chubukov (UMN) | |
| Title | Interplay Between Superconductivity and Non-Fermi Liquid at a QCP in a Metal | |
| Abstract | I discuss the interplay between non-Fermi liquid behaviour and pairing near a quantum-critical point (QCP) in a metal. These tendencies are intertwined in the sense that both originate from the same interaction mediated by gapless fluctuations of a critical order parameter. The two tendencies compete because fermionic incoherence destroys the Cooper logarithm, while the pairing eliminates scattering at low energies and restores fermionic coherence. I discuss this physics for a class of models with an effective dynamical interaction V Ω ~1/|Ω|y (the y-model). This model describes, in particular, the pairing at a 2D Ising-nematic critical point (y=1/3), a 2D antiferromagnetic critical point (y=1/2) and the pairing by an Einstein phonon with vanishing dressed Debye frequency (y=2). I argue the pairing wins, unless the pairing component of the interaction is artificially reduced, but the pairing mechanism is fundamentally different from BCS and is associated with the emergence of complex exponents for the pairing susceptibility. I will further argue that there is a topological transition in the y-model, at y=2. | |
| Host | Yuxuan Wang | |
October 13 - SPECIAL SEMINAR |
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| Speaker | Shuyi Li (Rice University) | |
| Title | Topological bosonic excitations in frustrated magnetic systems | |
| Abstract | Topological band theory has emerged as one of the central themes in condensed matter physics. In analogy with electrons, the bosonic excitations from spin waves (magnons) and lattice vibrations (phonons) can also exhibit non-trivial topological properties in magnetic insulators with broken inversion or time reversal symmetry. In this talk, I will showcase two such examples: first, I shall discuss the topological magnons and the associated thermal Hall effect in a layered honeycomb ferromagnet [1] motivated by the discovery of CrI3. We find several topological phase transitions and Weyl magnon behavior induced by the interlayer coupling. Second, I will discuss another type of topological bosonic excitations, the polaritons, arising from the magnon-phonon hybridization in a monolayer antiferromagnet FePSe3 [2].
[1] Topological Weyl magnons and thermal Hall effect in layered honeycomb ferromagnets, S. Li and A. H. Nevidomskyy, Phys. Rev. B 104, 104419 [2] Topological magnon-phonon hybridization in two-dimensional antiferromagnets, J. Luo, S. Li, Z. Ye, R. Xu, H. Yan, J. Zhang, G. Ye, L. Chen, D. Hu, X. Teng, W. A. Smith, B.I. Yakobson, P. Dai, A. H. Nevidomskyy, R. He, H. Zhu (under review of Nature Communications) |
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| Host | Chunjing Jia | |
October 17 |
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| Speaker | Armita Nourmohammad (University of Washington) | |
| Title | Learning the shape of the immune and protein universe | |
| Abstract | The adaptive immune system consists of highly diverse B- and T-cell receptors, which can recognize a multitude of diverse pathogens. Immune recognition relies on molecular interactions between immune receptors and pathogens, which in turn is determined by the complementarity of their 3D structures and amino acid compositions, i.e., their shapes. Immune shape space has been previously introduced as an abstraction of molecular recognition in the immune system. However, the relationships between immune receptor sequence, protein structure, and specificity are very difficult to quantify in practice. In this talk, I will discuss how the growing amount of immune repertoire sequence data together with protein structures can shed light on the organization of the adaptive immune system. I will introduce physically motivated machine learning approaches to learn representations of protein micro-environments in general, and of immune receptors, in particular. The learned models reflect the relevant biophysical properties that determine a protein's stability, and function, and could be used to predict immune recognition and to design novel immunogens e.g. for vaccine design. | |
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October 24 |
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| Speaker | Richard Greene (University of Maryland) | |
| Title | Strange metal transport, ferromagnetism and the Planckian scattering rate limit in electron-doped cuprates | |
| Abstract | I will discuss recent transport studies on thin films of the electron-doped cuprate system La2-xCexCuO4 that exhibit strange metal transport in the normal state down to 35 mK. These results strongly suggest that the high-Tc superconductivity emerges from this strange metal normal state. The strange metal behavior is manifested as a linear-in-T resistivity from 35 mK to 20K and a ~T^2 resistivity from 50K to 400K over a range of doping above and below a Fermi surface reconstruction at x = 0.14 [1-2]. Other indications of strange metal behavior include a low temperature linear-in-H magnetoresistance and a low temperature lnT thermopower [3-5] over the same range of doping. At the present time these results have not been explained and they represent a challenge to the theory of the cuprates.
In addition, I will discuss a study of these films via a combination of dc conductivity and optical conductivity [6], which shows that the electron scattering rate far exceeds the conjectured Planckian bound on inelastic scattering at temperatures above 20K. This suggests that recent highly publicized claims of a Planckian bound on transport in solids are not universal and that the temperature dependence of the normal state resistivity of the cuprates remains an unexplained mystery. If time permits I will discuss experiments that suggest ferromagnetism exists below 4K for electron-doping beyond the superconducting dome [7]. References [1]. T. Sarkar et al., Phys. Rev. B 103, 224501 (2021) [2]. T. Sarkar et al., Phys. Rev. B 98, 224503 (2018) [3]. R. L. Greene et al., Ann Rev Cond. Matt. Phys. 11, 213 (2020) [4]. T. Sarkar et al., Sci. Adv. 5, eeav6753 (2019) [5]. P. R. Mandal et. al., PNAS 116, 5991 (2019) [6]. N. R. Poniatowski et al., Phys. Rev. B 104, 235138 (2021) [7]. T. Sarkar et al., Science 368, 532 (2020). |
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| Host | David Tanner and Peter Hirschfeld | |
October 31 |
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| Speaker | Qiong Yang (University of Michigan) | |
| Title | From molecules to development: biological timing and patterning | |
| Abstract | Organisms from bacteria to humans employ complex biochemical or genetic oscillatory networks, termed biological clocks, to drive a wide variety of cellular and developmental processes for robust timing and patterning. Despite their complexity and diversity, many of these clocks share the same core architectures that are highly conserved from species to species, suggesting an essential role of network structures underlying clock functioning. The Yang lab, bridging biophysics, quantitative systems biology, and the young field of bottom-up synthetic biology, has integrated modeling with experiments in minimal cells and live embryos to elucidate universal physical mechanisms underlying these complex processes. In this talk, I will focus on our recent efforts in understanding the design and interaction of cellular clocks of cell cycles and a developmental clock to control segmentation patterns. Computationally, we have identified network motifs, notably incoherent inputs, that enhance robust performance. Experimentally, we developed artificial cells in microfluidic droplets to analyze circuits and functions of robustness and tunability. We also established single-cell assays of zebrafish embryos combined with biomechanics to analyze the role of energy and mechanical and biochemical signaling in spatiotemporal patterns. | |
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November 2 - SPECIAL SEMINAR at 1:00pm in Room 2165 |
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| Speaker | Daniel Rhodes, MSE & Physics, University of Wisconsin-Madison | |
| Title | Moving Beyond Graphene and 2D Semiconductors: Superconductivity and Ferroelectricity in Few-Layer Td-MoTe2 | |
| Abstract | 2D materials are layered materials that may be readily exfoliated down to a single atomic layer, presenting an opportunity to control electronic states and magnetic ordering noninvasively and efficiently. In this talk, I discuss the materials challenges faced by the 2D community in exploring novel 2D materials beyond graphene and 2D transition metal dichalcogenide semiconductors. The materials challenges are not trivial to solve, and meaningful solutions must include complete control over material synthesis and device fabrication, in combination with contact engineering. After discussing these challenges, I will follow up an example material (Td-MoTe2), whereby solutions to the materials challenges allow us to probe how topology emerges from the bulk down to monolayer thicknesses for Td-MoTe2. We will explore how the influence of an electrostatic gate allows us to identify a unique superconducting state in bilayer Td-MoTe2 and its profound influence even when no change in the chemical potential is made. Our results indicate that superconductivity in bilayer Td-MoTe2 can be completely quenched by an electrostatic gate, and that the superconducting behavior is connected to Fermi surface nesting between electron and hole pockets. Not only, because of the monoclinic crystal structure ferroelectric behavior is established and its effects on superconductivity investigated. | |
| Host | Xiao-Xiao- Zhang | |
November 7 |
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| Speaker | Alexander Balatsky (U. Connecticut) | |
| Title | Quantum Materials and Dark Matter Sound | |
| Abstract | I will outline the ideas of using quantum matter for dark matter (DM) detection. The lower end of dark matter particles mass make it possible to use collective modes of condensed matter systems for dark matter detection[1,2]. I will outline recent proposal using materials with entangled quantum orders as detectors for DM[3]. I will also outline recent discussion of Dark Matter sound mode as another excitation that can be used for DM detection[4].
[1]Materials informatics for dark matter detection RM Geilhufe, B Olsthoorn, AD Ferella, T Koski, F Kahlhoefer, J Conrad, physica status solidi (RRL)âpid Research Letters 12 (11), 1800293 (2018) [2]Mass fluctuations and absorption rates in dark-matter sensors based on Dirac materials B Olsthoorn, AV Balatsky Physical Review B 101 (4), 045120 (2020) [3]Axion-matter coupling in multiferroics HS Roising, B Fraser, SM Griffin, S Bandyopadhyay, A Mahabir, Physical Review Research 3 (3), 033236 (2021) [4]Dark sound: Collective modes of the axionic dark matter condensate AV Balatsky, B Fraser, HS Roising, Physical Review D 105 (2), 023504 (2022) |
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| Host | Peter Hirschfeld | |
November 9 - Special Seminar at 2pm in 2260 |
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| Speaker | Brian Cowan (Royal Holloway College) | |
| Title | NMR as a probe of many body dynamics and collective excitations | |
| Abstract | Nuclear Magnetic Resonance Techniques are proving to be a especially valuable for probing many modern many body problems from fluctuations in unconventional superconductivity to the fundamental dynamics of quantum fluids at very low temepratures. The talk will review the NMR theory that probes collective behaviors along with modern examples. | |
| Host | Neil Sullivan | |
November 14 |
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| Speaker | Li Fang (UCF) | |
| Title | Ultrafast X-ray and XUV spectroscopy of charge dynamics in molecular systems | |
| Abstract | Thanks to recent advances in laser and light source technology, the scientific investigation of the fundamental aspects of photointeractions with the basic building blocks of matter is now possible in both the short and long wavelength regime. I will present recent research and future opportunities of using ultrafast photon sources for time-resolved studies of charged-particle dynamics subsequent to the initial photoionization or photoexcitation of isolated as well as aggregated atomic and molecular systems. I will discuss the necessary photon source parameters that enable advanced spectroscopic methods and the insightful information these time-domain and multi-dimensional experimental methods can possibly achieve. Specifically, I will present a study of the photo-induced electron motion with attosecond pulses in the XUV and x-ray regime at the atomic spatial and temporal resolution and a study of the formation of nanoplasmas in gaseous clusters using ultrashort laser pulses at short and long wavelength. Finally, I will introduce the capabilities of a User Facility for Attosecond Soft x-rays and Terahertz (UFAST) which will be constructed at University of Central Florida. | |
| Host | Xiao-Xiao Zhang | |
November 21 |
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| Speaker | Robb Moore (ECE, UF) | |
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| Host | Yoonseok Lee | |
November 28 |
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| Speaker | Daniel Weissman (Emory) | |
| Title | SARS-CoV-2 evolution within and between hosts | |
| Abstract | The global population of SARS-CoV-2 is structured into discrete infections within hosts. How does this affect the evolution of the pandemic? First, I will show how one can use the evolution between pairs of hosts to infer how many virus particles contribute to a new infection. Second, I will discuss how the observed timing and dynamics of the Variants of Concern suggest that rare chronic infections are the key drivers of global infection. Finally, I will briefly touch on a case study of rapid evolution and diversification within a chronic infection. | |
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December 5 |
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| Speaker | Andriy Nevidomskyy (Rice) | |
| Title | Quantum Melting of Spin `Solids' in 2D | |
| Abstract | For several decades, the attention of both theoretical and experimental physicists has focused on finding examples of quantum spin liquids (QSL) exotic phases of matter characterized by the spin fractionalization, whereby the energy and momentum are carried not by spin waves, but by the emergent elementary excitations. By contrast, defining a quantum spin `solid' as a state that spontaneously breaks the lattice translation symmetry (be it via Né order or by forming a valence bond crystal), I will pose the following question how do quantum solids `melt' and how does entanglement establish itself in a QSL? To answer this question, I will present our recent work on several 2D systems, from the familiar spin-1/2 on a frustrated square lattice, to the perhaps less familiar models of spin-1 and SU(3) objects. We study these models using the density matrix renormalization group (DMRG) and infinite projected entangled-pair states (iPEPS) techniques, supplemented by the analytical mean-field and linear flavor wave theory calculations. In the last part of the talk, I will discuss another mechanism of quantum `melting,' induced by a strong magnetic field the conventional picture is that this process can be understood as a BoseEinstein condensation of the auxiliary bosons. Here we show that a more exotic, non-BEC transition occurs when magnetic frustration drives the system across the Lifshitz point, and we find an exotic bosonic liquid that avoids the BEC altogether so-called Bose metal with algebraic correlations. | |
| Host | Peter Hirschfeld | |
December 12 |
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