Condensed Matter/Biophysics Seminars
Spring 2021

Condensed Matter/Biophysics Seminars are via Zoom until further notiice
on Mondays @ 4:05 pm to 4:55 pm

Contact: Yasu Takano or Dmitrii Maslov

January 11
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January 18 (No seminar – MLK Jr Day)
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January 25
	Speaker	Bo Zhen (Univ. of Pennsylvania)
	Title	Topological photonics at the nanoscale
	Abstract	Topological photonics has been of great interest due to both fundamental principles and potential applications. In this talk, I will discuss some of our recent results in linear and nonlinear nanophotonic structures, where topological phenomena are achieved. Their applications in photonics integrated circuits and nonlinear optoelectronic devices will also be discussed.
	Host	Xiao-Xiao Zhang

February 1
	Speaker	Yin-Chen He (Perimeter Institute for Theoretical Physics)
	Title	Stiefel liquids: from the Dirac spin liquid to a new critical spin liquid
	Abstract	I will talk about a new type of critical quantum liquids, dubbed Stiefel liquids, that can emerge from the intertwinement of symmetry breaking orders. Our theory is based on 2+1 dimensional nonlinear sigma models on target space SO(N)/SO(4), supplemented with Wess-Zumino-Witten terms. We argue that the Stiefel liquids form a class of critical quantum liquids with extraordinary properties, such as large emergent symmetries, a cascade structure, and nontrivial quantum anomalies. We show that the well known deconfined quantum critical point and U(1) Dirac spin liquid are unified as two special examples of Stiefel liquids, with N=5 and N=6, respectively.Furthermore, we conjecture that Stiefel liquids with N>6 are non-Lagrangian, or in other words are beyond any mean-field descriptions including parton constructions. We further predict that the some of the non-Lagragian Stiefel liquids can be realized as a critical spin liquid in frustrated quantum spin systems, for example, on triangular or kagome lattice, through the intertwinement between non-coplanar magnetic orders and valence-bond-solid orders.
	Host	Yasu Takano

February 8
	Speaker	Yi Li (Johns Hopkins Univ.)
	Title	Topological superconducting and many-body orders in doped semimetals
	Abstract	Electrons in a material can synchronize to exhibit collective effects and various ordered states. I will discuss novel superconducting and density wave orders which capture the topology of the gap function rather than that of quasiparticle states only. The nontrivial geometric phases of Cooper pairs and their non-Abelian generalization lead to fundamentally new topological pairing orders.
.	Host	Yuxuan Wang

February 15
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February 22
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March 1
	Speaker	Jukka Pekola (Aalto Univ., Finland)
	Title	Quantum thermodynamics on superconducting circuits
	Abstract	I will start by introducing ideas and principles of how to realize thermodynamic phenomena and devices in circuits composed of superconducting elements, including qubits, combined with heat baths formed of on-chip electronic reservoirs. This way we have demonstrated quantum-limited heat transport by microwave photons [1,2], quantum heat valves [3] and rectifiers [4] and ultrasensitive calorimetric detectors [5]. Towards the end of the talk I will present how we plan to realize quantum heat engines and refrigerators based on thermodynamic cycles [6] and considerations on ultimate energy resolution of nanocalorimeters [5,7,8]. [1] M. Meschke, W. Guichard, and J.P. Pekola, Nature 444, 187 (2006). [2] A.V. Timofeev, M. Helle, M. Meschke, M. Möttönen, and J.P. Pekola, Phys. Rev. Lett. 102, 200801 (2009). [3] A. Ronzani, B. Karimi, J. Senior, Y.-C. Chang, J. T. Peltonen, C.D. Chen, and J.P. Pekola, Nat. Phys. 14, 991 (2018). [4] J. Senior, A. Gubaydullin, B. Karimi, J.T. Peltonen, J. Ankerhold, J.P. Pekola, Comm. Phys. 3, 40 (2020). [5] B. Karimi, F. Brange, P. Samuelsson, and J. P. Pekola, Nat. Commun. 11, 367 (2020). [6] B. Karimi and J. P. Pekola, Phys. Rev. B 94, 184503 (2016). [7] B. Karimi and J.P. Pekola, Phys. Rev. Lett. 124, 170601 (2020). [8] J. P. Pekola and B. Karimi, in preparation.
	Host	Yasu Takano

March 8
	Speaker	Wei Xue (UF)
	Title	Superfluid effective field theory
	Abstract	In this talk, I will present new developments in an effective field theory (EFT) of helium superfluid. One of the motivation to build this framework is to understand a test particle scattering of the superfluid with its de Broglie wavelength shorter than the average helium spacing. The scattered helium atom will produce a few to thousands of quasi-particles. Due to mixing with different momentum scales, a naive EFT of the superfluid breaks down, but a novel EFT is introduced to describe how helium atoms decay to quasi-particles and quasi-particles are thermalized.
	Host	Tarek Saab

March 15
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March 22
	Speaker	Pinshane Huang (Univ. Illinois Urbana-Champaign)
	Title	How stiff are 2D materials? Designing ultrasoft electronic materials using insights from electron microscopy
	Abstract	Understanding the deformation and bending of two-dimensional (2D) materials is critical for the realization of next-generation electronics and nanomechanical devices. For example, while the mechanics of few-layer graphene have been studied for more than a decade, there is still no consensus on basic properties such as its bending stiffness and how it scales with thickness. In addition, defect and strain engineering of 2D materials is an emerging area of research, where homogeneous or heterogeneous alloying can stabilize exotic electronic phases such as Weyl semimetals or pattern the properties of 2D nanoelectronics and optoelectronics on the nanoscale. Electron microscopy provides a powerful platform for addressing these challenges by enabling measurements of the conformation and strain of 2D materials at atomic resolution. In this talk, I will discuss our work using aberration-corrected scanning transmission electron microscopy (STEM) in order to probe and quantify these deformations in 2D materials at the atomic scale. This work is divided into two areas: 1) using machine learning to expand the precision of atomic resolution STEM in order to visualize local picometer-scale strain fields and understand how single-atom defects interact with the surrounding lattice and 2) using STEM in combination with mechanical modeling to reveal an unusual, slip-mediated softening of graphene and other 2D materials. Our results indicate that the bending stiffness of few layer graphene can be orders of magnitude smaller than previously thought and provide a new lower limit for the fabrication of ultra-soft, high mobility electronic nanodevices based on 2D materials. As a bonus, I will also talk about our recent work imaging small molecules at atomic resolution on graphene substrates.
	Host	Kathryn McGill

March 29
	Speaker	Eduardo Fradkin (Univ. Illinois Urbana-Champaign)
	Title	Duality in condensed matter and high energy physics
	Abstract	I will discuss the subject of duality transformations in condensed matter and in high energy physics both from a historical and modern perspectives. I will focus on the role of recently discovered dualities in 2+1 dimensions in the problem of the quantum Hall plateau transitions and in the theories of non-Abelian quantum Hall states.
	Host	Yuxuan Wang

April 5
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April 12
	Speaker	Serena Bradde (American Physical Society)
	Title	The dimension of a complex system: a physicist perspective
	Abstract	A fundamental problem in science is uncovering the effective number of dynamical degrees of freedom in a complex system. For many real systems, the dimension changes on the spatio-temporal scale at which the system is observed, making the problem of dimensional reduction hard to solve. In this talk, I will propose an approach to describe ‘effectively’ the behavior of complex systems by drawing an analogy with the Renormalization Group.
	Host	Purushottam Dixit

April 19
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