569 Emergent States of Matter

Term essays Spring 2021

These essays were written by students taking Physics 569 Emergent States of Matter, Spring 2021, at the University of Illinois at Urbana-Champaign. The copyright of each essay is due to the author.

Please acknowledge the essay title, author, and this course in any citation to these articles.

The information, opinions and interpretations expressed are those of the authors, not necessarily those of the instructor.


Author: Nan Zhang

Title: Cosmic Strings

Abstract:

This essay discusses the generating, gravitational description and observable effects of cosmic strings. In this essay, cosmic strings, as linear topological defects, are shown to be generated by the spontaneously symmetry breaking of gauge fields during the inflationary era. By studying the metric around a single infinite-length straight cosmic string, we explain carefully how the cosmic string changes a flat space into a conical space and results in the deflection of light passing by. We explore the double images, accretion effects and CMB anisotropy caused by the cosmic strings and introduce the efforts to detect cosmic strings based on the observable effects.


Author: Mark Hirsbrunner

Title: Odd Viscosity in Chiral Active Matter: Theory and Experiment

Abstract: Chiral active matter is a hydrodynamic phase composed of self-spinning microscopic constituent particles. The non-equilibrium steady states of chiral active matter realize a novel dissipationless transport coefficient called the odd viscosity. In this paper I provide an overview of theories regarding the formation of odd viscosity in chiral active matter, both from a top-down hydrodynamic perspective and from a bottom-up microscopic perspective. Fluids with an odd viscosity support exotic topological waves and surface flows not found in conventional fluids. I briefly discuss the theory underlying these novel features and present experiments that observe these effects in two very different chiral active fluids.


Author: Adam Bauer

Title: On the emergence of flocking in birds

Abstract: This essay will provide a brief overview of the many approaches scientists have taken to study bird flocking, including numerical, observational, and analytic methods. We discuss the pioneering work first done in numerical modeling and theoretical physics, and how these approaches are challenged by observational data. Lastly, we discuss an observationally motivated theoretical framework for studying flocking.


Author: Chenghao Zhang

Title: Experiment and Theory of Glass transition

Abstract:
Though belong to well-known state of matter, microscopic understanding of glassy state is still challenging for scientists. This article will summarize theoreticaland experimental effort have been made to unveil mystery of glass, begin with experimental phenomena like dramatic change of viscosity below glass transition temperature Tg , fragility, aging and dynamical correlation function of glass etc. For theoretical side, we emphasize random first-order transition theory of glass
transition studied by Peter Wolynes.


Author: Zihan Wang

Title: Emergent Ecology: Neutral Theory of Ecosystems

Abstract: This essay discusses the neutral theory (NT) of ecosystems, from the aspects of analytical model, simulation results and comparison to empirical data. Certain macroecological properties are shown to be emergent from NT. It also discusses how the neutrality itself could be viewed as an emergent property from evolutionary dynamics, and how can the NT be possibly be reconciled with the classical niche theory.


Author: Marc Klinger

Title: Evolutionary Game Theory – From Cooperation to Topological Phases

Abstract:

In this essay, we provide an introduction to the machinery of Rational and Evolutionary Game Theory, and observe how complex and even potentially counter-intuitive phenomena can emerge therein from a relatively simple set of strategic interactions.


Author: Riley Vesto

Title: Turing Pattern Formation from Reaction-Diffusion Equations and Applications

Abstract:

Turing patterns are finite-wavelength, stationary formations which can develop from homogeneous initial conditions following local reaction-diffusion equations. This essay provides a phenomenological description of how Turing patterns form, describes methods of preparing Turing patterns, and provides some examples of Turing patterns which appear in nature.


Author: Rajas Chari

Title: Network theory applications in complex systems

Abstract: Network theory provides a great framework to study a myriad of phenomena occurring in nature. In this report we describe the different ways in which networks are characterized by studying empirical networks. We then study the popular descriptive models used to build and study networks with properties similar to empirical networks. We also explore methods from physics which can be used to analyze networks, including statistical mechanics and dynamical systems. Finally, we discuss the potential of renormalization group theory to study networks.


Author: Shengzhu Yin

Title: Hidden Geometry and Coarse-graining Metabolism Network

Abstract:

Network Cartography is a key visualization of an organism’s mechanism of processing. In a sense, life is an ultimate emergent phenomenon that can be found in nature. However, most cartography only contains topological information, i.e., a mathematical graph. In this essay, we will take a look into series of recent development that further incorporates geometrical information into these metabolic cartography. As a final result, we will see an emergent pattern by utilizing this additional information.


Author: Kuan-Sen Lin

Title: Topological solitons in liquid crystals

Abstract: Ordered media such as liquid crystals (LCs) provide a platform to realize and manipulate nontrivial field configurations in which topological solitons can emerge and behave like particles. In this term essay, we describe some of the most recent studies on numerical modeling, experimental observation, and manipulation of various topological solitons, such as hopfions, skyrmions, and heliknotons, in LCs. In particular, such topological solitons can be tuned electrically, and interact to form emergent structures, such as skyrmion bags and three-dimensional crystals.

Author: Jinchao Zhao

Title: The electron pairing of Iron-based Superconductors

Abstract: Iron-based superconductors are the second family of High-Tc super-conductors  people  have  found  until  now  besides  cuperates.   This  essay presents a review of experimental measurements on iron based superconductors, and aims at the difference and potential links between the pairing mechanism of these two families of high-Tc superconductors.


Author: Dmitry Manning-Coe

Title: Towards an emergent macroeconomics

Abstract:

Despite substantial interest after the financial crisis, interest in deriving macroeconomic phenomena as emergent quantities has waned. I will argue that the existence of robust scaling laws and fluctuations on the order of economic quantities themselves are the kinds of things that should be explained by an emergent framework. To make this plausible I will show how emergent frameworks in biology and population modelling are able to explain similar phenomena.


Author: Michael O’Boyle

Title: The Impact of Superfluids and Superconductors on Neutron Star Cooling

Abstract:

Neutron stars, remnants of stellar collapse whose densities exceed those of atomic nuclei, consist of a strongly interacting liquid of unbounded protons and neutrons (to first approximation) whose temperature is greatly below the Fermi temperature. They are subject to attractive nuclear interactions, so it is commonly believed that Cooper pairs will form in the degenerate matter. This would give rise to superfluid neutrons and superconducting protons. However, modelling degenerate nuclear matter remains an elusive problem, so little is known about the physics of the condensates. This essay will explore perhaps the most significant observational consequence of super-phases in neutron stars: their impact on the star’s rate of cooling from a thermal initial configuration into a degenerate ground state. Specifically, we will discuss Cassiopeia A, the youngest and most rapidly cooling known neutron star, observations of which have allowed constraints to be placed on the super-phase phenomena.


Author: Shubhang Goswami

Title: Particles may not be employed, if they don't pull themselves up by their boostraps

Abstract:

Our current understanding of physics lies in a reductionist approach. An attempt to put physics under a non-hierarchical footing more in line with Emergence was proposed by Chew in 1968. In this essay, I will explore this approach based on self-consistency, talk about its success, its decline, and its renewed life in critical phenomenon. I will describe how time could possibly emerge from the bootstrap approach. I will elaborate on possible future connections with different fields of physics that could benefit from the Bootstrap approach and vice versa. Finally, I will end with a brief remark on whether we can shed the idea of a particle.


Author: Vincent Hickl

Title: Dynamics of topological defects in passive and active liquid crystals

Abstract: Topological defects arise in a variety of physical systems that undergo symmetry-breaking phase transitions into a state of higher order. Liquid crystals (LCs) are a useful set of systems for studying the interactions of multiple defects, particularly their creation and mutual annihilation. In this essay, the basic interactions of defects in LCs are described through the lens of recent experimental and theoretical advances in (quasi-)2-dimensional systems. Then, recent findings in active nematics are described, demonstrating how non-equilibrium interactions can give rise to very different defect behaviors. Unlike equilibrium systems, active nematic liquid crystals can exhibit spontaneous defect creation, leading to turbulent-like dynamics. These systems exemplify how relatively simple interactions between many microscopic objects can lead to complex emergent phenomena at larger scales.


Author: Mayisha Zeb Nakib

Title: Active Flocks that Squawk: Geese on 2D Sheets

Abstract: This essay explores agent based modeling and the Vicsek model to help explain emergent behaviors of migrating snow geese on a 2D lake surface. We will also review other 2D biological flocks such as surf scooters on the ocean. In addition, we will cover 3D swarms of krill in a more recent paper that takes into account transfer entropy and mutual information to explain swarm behavior due to more complicated social interactions.


Title: Using entanglement to characterize topological phases of matter

Author: Faisal Alam

Abstract: Off diagonal long range order is often used to characterize emergent phenomena like ferromagnetism and superfluidity. Similarly entanglement entropy and entanglement spectrum can be used to characterize topological phases of matter.  In such phases the interplay between interactions, symmetry and topology lead to emergent fractional charge, fractional statistics and non-trivial edge states.  In this essay we review how entanglement signatures can be used to deduce these properties from the ground state of the system alone.


Author: Jairo M. Rojas

Title: Criticality in Living Systems

Abstract:

Various phenomena present in living systems, such as tissues, bacterial colonies, and neural networks, are the result of the interaction of a large number of components and, therefore, can be studied using statistical physics techniques. Thanks to new experimental technologies, it is now possible to study biological systems in detail and build statistical mechanics models directly from the data. Interestingly, the parameters for the models found are very close to a critical point. This essay describes experimental observations, simulations, and mathematical analyzes of biological systems where criticality has been found and discusses the presence of self-organizing criticality phenomena as a result of evolution.


Author:  Matthew Thibodeau

Title: Measurement-Induced Phase Transitions

Abstract:

When some unitary quantum circuits are punctuated by periodic measurements, distinct phases
can emerge, where the order parameter is related to the entanglement properties of the circuits.
This term paper describes recent progress in the identification and characterization of these phases.
We provide a selection of circuit models that exhibit this phenomenon, detail the analytic and
numerical arguments that show the emergence of high- and low-entanglement phases, and then
describe some important properties of the circuits and states that can emerge, including topological
protection and quantum error correction capabilities.


Author: Ryan Bogucki

Title: Criticality in living matter: a universal mechanism of charge transport in biomolecules

Abstract
In recent experimental works using metallic contacts attached to proteins, an
anomalously large, temperature-independent long-range conductance has been mea-
sured across numerous proteins with no known role in electron transfer processes.
The exact mechanism by which this phenomenon occurs is unknown, although
several recent theoretical works suggest that proteins belong to a larger class of
biomolecules tuned precisely to a metal-insulator critical point, where decoherence
plays a pivotal role for the robust conductance measured in proteins. Along with
having strong dependence on molecular conformation, the ubiquitous nature of the
phenomenon suggests that it was evolutionarily selected for, as the probability to
find even a single critical molecule by chance is astronomically low. In this paper, we
discuss the current modeling efforts which realize the physics for this phenomenon,
their relation to experiment, as well as potential evolutionary roles.


Author: Daniel Belkin

Title: Anderson Localization

Abstract
This work covers the theory of Anderson localization. The behavior of Anderson’s original model is discussed, as is the derivation of Wegner’s nonlinear σ model. A relationship to Goldstone’s theorem in this context is covered. We then discuss an experimental demonstration of Anderson localization in a three-dimensional ultracold atom system. Finally, extensions to weak interactions via theory and numerics are discussed.


Author: Chunyu Lu

Title:  The development of the inflation models

Abstract: This article is about different inflation models and phase transitions related to the models. We would focus on what kind of observational effects they can predict and explore different cosmological surveys to see the constrains they could give to the inflation model.


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