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Condensed Matter Seminar Thursday, November 21, 2024 3:30 PM Physics, Room 338 
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Condensed Matter Seminar Thursday, November 14, 2024 3:30 PM Physics, Room 338 
"Sarma and Bogomol'nyi Equations in Superconductivity"Mia Kyler , University of Virginia [Host: Eugene Kolomeisky]
ABSTRACT:
Secondorder differential equations are ubiquitous in physics, but every once in a while there are special cases where the order of these equations may be reduced. One example of such a reduction is the quantum harmonic oscillator as solved by P. Dirac. Dirac introduced the annihilation and creation operators, which permit solving of the secondorder problem presented by the linear Schrödinger equation by reduction to a firstorder linear equation. In the context of superconductivity, a system of nonlinear secondorder differential equations describing vortex lines in superconductors may be reduced to firstorder at a particular value of the GinzburgLandau parameter. This reduction can be achieved by two procedures. One approach uses an ingenious minimization of the GinzburgLandau free energy functional tailored to the presence of a topological defect (the Bogomol’nyi procedure). The other uses the GinzburgLandau equations and operators analogous to Dirac’s annihilation and creation operators (the Sarma procedure). The Bogomol’nyi procedure leads to the famous Bogomol’nyi equations, published in 1976. The Sarma procedure was never published in a journal but is hinted at in P. G. de Gennes’s 1966 classic Superconductivity of Metals and Alloys. We will show that, in the particular case of the vortex line, the Sarma procedure recovers the Bogomol’nyi equations and that the Sarma procedure is in fact more general, as to be applicable it does not rely upon the presence of a topological defect. 
Condensed Matter Seminar Thursday, September 5, 2024 3:30 PM Physics, Room 338 
"Monopole Hall effect in a metallic chiral magnet"Dr. Kotaro Shimizu , RIKEN, Japan [Host: GiaWei Chern]
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Topological spin textures like magnetic skyrmions exhibit a stable particle nature due to their topological protection, leading to their utilization as an information carrier in magnetic memory devices. Although exploring the fundamental currentinduced dynamics is a pivotal topic for such applications, the studies have been mostly limited to twodimensional skyrmions [1] and the systematic investigation for threedimensional (3D) magnetic hedgehogs remains largely unexplored. The topological defect at the core of the hedgehog where spin length vanishes, corresponding to monopoles of the emergent magnetic field for electrons, could bring about currentinduced dynamics distinct from skyrmions [2]. 
Condensed Matter Seminar Thursday, June 6, 2024 3:00 PM Physics, Room 323 Note special time. Note special room. https://kotaroshimizu.netlify.app/ 
"Latest Trends and Opportunities in Photoemission Spectroscopy"Luca Moreschini , University of California, Berkeley [Host: Despina Louca]
ABSTRACT:
The transition of many materials of interest for the condensed matter community, particularly in energyrelated applications, from crystalline materials to heterostructures and complex architectures, where different compounds are combined, stacked, interfaced and twisted in different ways, has forced the experimental techniques to evolve accordingly. Angleresolved photoemission (ARPES), which has been for decades a spectroscopy of reference for accessing the low energy excitations in solids, had to implement a number of updates to keep pace with the progress made in materials fabrication. This talk will discuss some of the latest trends in ARPES, how it has advanced and to where it is moving in order to remain an invaluable tool for studying the electronic properties of materials. 
Condensed Matter Seminar Thursday, April 25, 2024 2:00 PM Physics, Room 323 Note special time. Note special room. 
"Voxelated Bioprinting: Digital Assembly of Viscoelastic Bioink Particles"Liheng Cai , University of Virginia [Host: Bellave Shivaram]
ABSTRACT:
Analogues of pixels to twodimensional (2D) pictures, voxels –– in the form of small cubes or spheres –– are the basic units of threedimensional (3D) objects. Digital assembly of bioink voxels may provide an approach to engineering heterogeneous yet tightly organized 3D tissue mimics. However, this approach requires precisely manipulating highly viscoelastic bioink voxels in 3D space, which represents a grand challenge in both soft matter science and biomanufacturing. In this talk, I will introduce a voxelated bioprinting technology that enables the Digital Assembly of Spherical bioink Particles (DASP). First, I will discuss the criteria for the ondemand generation, disposition, and assembly of viscoelastic bioink droplets in an aqueous environment without the help of large interfacial tension. Second, I will describe how to use DASP to create 3D structures consisting of interconnected yet distinguishable bioink particles. Finally, I will share our recent progress in applying DASP to encapsulate islets into multiscale porous scaffolds to treat type 1 diabetes. I will also discuss immediate applications and emerging challenges associated with voxelated bioprinting. 
Condensed Matter Seminar Thursday, April 11, 2024 3:30 PM Gibson Hall, Room 211 Note special room. 
"Computational Approach to Compositionally Complex Materials "Diego Ibarra , University of Virginia [Host: Joe Poon]
ABSTRACT:
High Entropy Alloys (HEAs), also known as Compositionally Complex Alloys (CCAs), embody a transformative class of materials consisting of at least four elemental components. These new types of material open new horizons in alloy design for exploring new structural and functional material properties unknown in traditional alloys. However, the combinatorial nature of HEAs can result in compositional possibilities reaching into the billions or even trillions, making traditional studies challenging. This talk presents an indepth exploration of HEAs, starting with a foundational understanding of their unique characteristics and the importance of their complex phase behavior. It highlights the inherent challenges posed by the expansive compositional space and limitations of conventional materials discovery and design methodologies. The talk emphasizes the pivotal role of computational techniques that provides a strategic blueprint for highthroughput alloy design that accelerates the exploration and optimization of HEAs but also provides a deeper insight into their fundamental behaviors. 
Condensed Matter Seminar Thursday, April 4, 2024 11:00 AM Physics Building, Room 323 Note special time. Note special room. 
"Linearintemperature conductance in electron hydrodynamics"Leonid Levitov , MIT [Host: Dima Pesin]
ABSTRACT:
Linear temperature dependence of transport coefficients in metals is habitually ascribed to nonFermiliquid physics. In this talk we establish this behavior for 2D electron fluids, systems in which carrier collisions assist conduction, leading to resistance decreasing with temperature. As we will see, electron fluids with simple Fermi surfaces obey nonclassical hydrodynamics described by a loop representing the Fermi surface shape evolving in space and time. Replacing the fluid velocity dynamics with an amoebalike loop dynamics leads to a large family of longlived excitations manifest as multiple viscous modes. A cascade of these modes results in a linear T dependence that extends down to lowest temperatures, as well as a Kolmogorovlike fractional power 5/3 scaling of conductivity vs. wavenumber. These dependences provide a smoking gun for nonclassical hydrodynamics and are expected to be generic for stronglycorrelated 2D systems with nearcircular Fermi surfaces. 
Condensed Matter Seminar Thursday, March 28, 2024 2:00 PM Monroe Hall, Room 118 Note special time. Note special room. 
"Exploring the photoluminesce photoswitching properties of photochromic molecule crosslinked PbS quantum dots"Ephraiem Sarabamoun , University of Virginia [Host: Joshua Choi]
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Pairing PbS quantum dots (QDs) with photochromic molecules (PCMs) allows for the synthesis of efficient and reversible near infrared photoluminescence (PL) photoswitches. In our work, we explore the utility space of this hybrid system by systematically comparing and contrasting different types of PCMs and different sizes of QDs. We demonstrate that the amount of photoswitching observed can be affected by (1) varying the size of the QDs, (2) varying the length of the PCMs, (3) fluorinating the PCMs, (4) varying the end group of the PCMs. We further investigate this system to parse out the mechanisms which may be responsible for this behavior. We present strong evidence to suggest that the mechanism driving this switching effect is an interQD tunneling process. We demonstrate a possible link between the energy levels of the PCMs and the magnitude of the switching effect and outline a rough empirical model which can guide the future design of QD/PCM photo switches to produce customized switching properties. 
Condensed Matter Seminar Thursday, March 28, 2024 3:30 PM Gibson Hall, Room 211 Note special room. 
"Intertwining Topology and Geometry: Topological hydrodynamics on curved magnetic membranes"Chau Dao , UCLA [Host: GiaWei Chern]
ABSTRACT:
In this talk, I will discuss our recent work on transport phenomena stemming from the topological properties of magnetic textures. As a specific illustrative case, we study the transport of vorticity on curved dynamical twodimensional magnetic membranes. We find that topological transport can be controlled by geometrically reducing symmetries, which enables processes that are not present in flat magnetic systems. To this end, we construct a vorticity 3current obeying a continuity equation, which is immune to arbitrary local disturbances of the magnetic texture as well as spatiotemporal fluctuations of the membrane. We show how electric current can manipulate vortex transport in geometrically nontrivial magnetic systems. As an example, we propose a minimal setup that realizes an experimentally feasible energy storage device and discuss its thermodynamic efficiency in terms of a vorticitytransport counterpart of the thermoelectric “ZT” figure of merit. 
Condensed Matter Seminar Thursday, March 21, 2024 3:30 PM Gibson Hall, Room 211 Note special room. 
"Study of magnetic and electronic properties of honeycomb layered MTiO3 (M= Mn, Co, Ni) ilmenites"Srimal Rathnaka , University of Virgina [Host: Despina Louca]
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Despite identical R3 crystal structures, honeycomb layered MTiO_{3} ilmenites exhibit diverse magnetic orders and transition temperatures (T_{N}): Gtype antiferromagnetic for MnTiO_{3} (T_{N}=68 K) and Atype antiferromagnetic for CoTiO_{3}(T_{N}=38 K) and NiTiO_{3} (T_{N}=22 K). This work focuses on this intriguing interplay between local structure, electronic properties, and magnetic configurations. CoTiO_{3} has two magnon peaks around 514 meV with a distinct gapless Dirac node nestled between them are observed and the magnon modes are renormalized to lower energies. For CoTiO_{3}, magnetic excitations attributed to spinorbit exciton multiplet transitions show the same temperature dependance as magnon with the intensity dissipating quickly above T_{N}. The energy levels arising from crystal field and spinorbit coupling are gradually thermally populated through T_{ }and reaching maximum at 100 K. However, the NiTiO_{3} system shows a single low energy magnon peak around 24 meV which is renormalized into lower energies, but it does not show Dirac magnon properties. The calculated exchange interactions using SpinW confirm the weaker interplane interaction in CoTiO3 than NiTiO3. Across three system, both transition metal M^{+2} ion and Ti^{+4} ions are in distorted octahedra environment, and the first four nearest neighbors are TiO < MO < TiO < MO with the given bond length order. Across three systems TiO and short MO bond length variation is minimum. However, MO bond length (MnTiO_{3}=2.28 Å, CoTiO_{3}=2.17 Å and NiTiO_{3}=2.12 Å) variation is significant which follows the same variation as reported dielectric constants (MnTiO_{3}=20.4, CoTiO_{3}=19.5 and NiTiO_{3}=17.8 ) and T_{N} and confirms the interplay between these parameters. Within the measured 100 K to 500 K, temperature dependance of local structure is insignificant and for the reported relative dielectric values, the variation is almost constant. This suggests that the interplay between local geometry and magnetic interactions governs the diverse behaviors observed in these honeycomb materials. 
Condensed Matter Seminar Thursday, February 22, 2024 11:00 AM Physics, Room 323 Note special time. Note special room. 
"Exploring emergent quantum phases in twodimensional flat band systems"JiangXiazi Lin , Brown University [Host: Seunghun Lee]
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Quantum phases such as superconductivity and ferromagnetism are among the most important topics in condensed matter physics research. Recently, a family of twodimensional flat band systems, including magicangle twisted graphene, uncovered an abundance of symmetry breaking and novel quantum phases. In this talk, I will introduce the recent advances in these materials and give two examples of how we engineered and revealed new quantum phases of matter in twisted graphene. These include an orbital ferromagnetic state induced by spinorbit coupling and a zerofield superconducting diode effect. Towards the end of the talk, I will mention our ongoing effort of studying a new type of Coulombdriven rotational symmetry breaking state in the moiréless bilayer graphene. These examples establish the twodimensional flat band systems as a versatile platform with multiple tuning knobs, where new physics emerges from the interplay between various quantum phases. 
Condensed Matter Seminar Monday, February 12, 2024 2:00 PM Physics, Room 323 Note special date. Note special time. Note special room. A recording of this talk is available at this link (use passcode #D8FWkr?). 
"Ultranodal state in multiband spin1/2 superconductors"Peter Hirschfeld , University of Florida [Host: Bellave Shivaram]
ABSTRACT:
Recent measurements on the tetragonal phase of the ironbased superconductor FeSe,S support the existence of a remarkable phase where the superconducting state supports a finite residual density of states arising from patchlike nodal surfaces[1,2]. This ``ultranodal"> state can arise in situations where conventional intraband spin singlet pairing is highly anisotropic and coexists with timereversal symmetry breaking interband spin triplet interactions [3]. Here I present a microscopic scenario including ferromagnetic interactions that can account for nonunitary pairing and C4 symmetry breaking in the superconducting state that is also observed in recent experiments.
1) Sato, Y. et al. Abrupt change of the superconducting gap structure at the nematic critical point in FeSe1xSx. Proc. Natl Acad. Sci. 115, 1227??1231 (2018). 2) Hanaguri, T. et al. Two distinct superconducting pairing states divided by the nematic end point in FeSe1xSx. Sci. Adv. 4, eaar6419 (2018). 3) ``Topologically protected ultranodal state in ironbased superonductors", S. Setty, S. Bhattacharyya, Y. Cao, A. Kreisel and P.J. Hirschfeld, Nat. Comm. 11, 523 (2020).

Condensed Matter Seminar Thursday, February 8, 2024 3:30 PM Physics, Room 323 Note special room. 
"Nanoscale quantum sensing of programmable quantum matter"Shaowen Chen , Harvard University [Host: Seunghun Lee]
ABSTRACT:
Characterization and quantum control of complex quantum matter is one of the shared goals for condensed matter and quantum information science research. Toward this end, my research uses van der Waals materials to synthesize topological and correlated states, and quantum sensors based on spin defects to uncover their microscopic picture. Focusing on superconductivity as the theme of this talk, I will first present pathways to program the electron correlation by exploiting the lattice degree of freedom, both in the planar and vertical directions of moiré materials. The challenges to fully characterize the moiré superconductivity will be discussed. In the second part, I will show new experimental observables unlocked by the nanoscale quantum sensing platform can uncover hidden physics. As an example, quantitative visualization of the super current flow in a Josephson junction is used to reveal electrically configurable ground states in the zeroresistance regime. A surprising role of the kinetic inductance and the implications for the Josephson diode effect will be discussed. Finally, I will share my vision to explore intertwined topology and correlation by integrating the programmable quantum materials with nanoscale quantum sensors. 
Condensed Matter Seminar Thursday, February 1, 2024 3:30 PM Physics, Room 323 Note special room. A recording of this talk is available at this link (enter passcode *0m4DSym). 
"Novel Fabrication of Quantum Wires: Towards Fractionalized Excitations"Tomoya Asaba , Kyoto University [Host: Seunghun Lee]
ABSTRACT:
The quest for novel quantum states in condensed matter physics often hinges on the reduction of system dimensionality. In particular, onedimensional systems are theoretically predicted to host a range of fractionalized excitations. These include the TomonagaLuttinger liquid, which exhibits spin and charge separation, and the Majorana particle, a cornerstone for faulttolerant quantum computing. However, fabricating nearperfect onedimensional quantum wires has been a significant challenge, especially those involving strongly correlated electrons. 
Condensed Matter Seminar Monday, January 29, 2024 2:00 PM Physics, Room 323 Note special date. Note special time. Note special room. A recording of this talk is available at this link (enter passcode ^Sa3J2OZ). 
"Nextgeneration artificial van der Waals quantum materials "Dr. Bumho Kim , University of Pennsylvania [Host: Seunghun Lee]
ABSTRACT:
If one can control the atomic symmetries of a material at will, the intrinsic properties of the material will be significantly modified. However, the atomic structures of conventional materials are often constrained by the equilibrium phase of matter. Here, we overcome this fundamental limitation using recent advances in twistronics, enabling precise control over all the individual point group symmetry elements – inversion, mirror, and rotational symmetries – in twisted van der Waals (vdW) material in a new 3D configuration [1]. The resulting 3D twisted materials exhibit emerging optical responses that are fundamentally different from those of natural vdW materials. This novel approach to control symmetries can enable nearly infinite vdW quasicrystalline phases, promising a practical platform to study lessexplored structureproperty relationships of quasicrystals. In addition, we will discuss an ultraclean vdW crystal synthesis method [2]. A selfflux synthesis method we developed has yielded vdW materials with ~ 2 orders of magnitude lower point defect density compared to commercial vdW materials grown by a chemical vapor transport method. These ultraclean vdW materials reveal intrinsic excitonic properties that were previously obscured by lowquality materials. The combination of these ultraclean materials with the symmetry design approach holds great promise for the development of highperformance artificial material systems for nextgeneration technologies.
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Condensed Matter Seminar Thursday, January 25, 2024 3:30 PM Physics Building, Room 323 Note special room. A recording of this talk is available at this link (enter the passcode @mJua4k1). 
"Roomtemperature and manybody quantum states in topological materials "Md. Shafayat Hossain , Princeton University [Host: Seunghun Lee]
ABSTRACT:
Topological states of matter combine quantum physics with topology—a branch of mathematics that explores geometric properties preserved under deformation. Quantum topology can lead to incredible properties. For instance, in a topological insulator, conducting edge states exist within an insulating bulk. Despite continuing progress, the search for such new quantum phases remains a central theme of condensed matter physics. In this talk, I will introduce two of the most soughtafter quantum states—roomtemperature topology and topological exciton insulator. I will first discuss our spectroscopic observation of topological edge states in Bi_{4}Br_{4}. I will show that the topological states, which typically can only be observed at temperatures around absolute zero, survive here at room temperature. I will also show how we probe the quantum transport response of this edge state using quantum interference. These observations mark the first steps in demonstrating the potential of topological materials for energysaving applications. In the second part of my talk, I will discuss our discovery of a unique topological state in Ta_{2}Pd_{3}Te_{5}. Here, the Coulomb interactions pair fermions (electrons and holes) into bosons (excitons), leading to a superfluid condensate state in the bulk while hosting topological edge states on the boundary. Finally, I will touch upon how these discoveries suggest exciting possibilities. This includes new devices and experimental techniques to discover the fundamental physics of topological quantum matter, opening doors for more efficient roomtemperature devices and quantum information technology. 
Condensed Matter Seminar Monday, January 22, 2024 2:00 PM Physics, Room 323 Note special date. Note special time. Note special room. 
"Nonlinear Optical Spectroscopies for Resolution of Electronic Structure and Dynamics"Veronica Policht , U.S. Naval Research Laboratory [Host: Despina Louca]
ABSTRACT:
Rapid and efficient charge transfer following absorption of light is a process of intense interest from the 
Condensed Matter Seminar Thursday, January 18, 2024 3:30 PM Gibson Hall, Room 211 Note special room. A recording of this talk is available at this link (enter the passcode UEd*U6Wr). 
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