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- Volume 12, 2021
Annual Review of Condensed Matter Physics - Volume 12, 2021
Volume 12, 2021
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Have I Really Been a Condensed Matter Theorist? I'm Not Sure, but Does It Matter?
Vol. 12 (2021), pp. 1–13More LessMy life as a physicist has been a blend of field theory, statistical physics, and condensed matter physics over half a century.
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A Career in Physics
Vol. 12 (2021), pp. 15–28More LessOver the course of my career, I have had the opportunity to work on a wide variety of problems in condensed matter physics, benefiting from superb collaborators and environments full of inspiring colleagues. I review here some highlights of my journey so far. Subjects include theories of dynamic critical phenomena, phase transitions in two-dimensional systems, systems with strong disorder, quantum physics of mesoscopic systems, one-dimensional quantum systems, and the quantum Hall effects.
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Mechanical Frequency Tuning by Sensory Hair Cells, the Receptors and Amplifiers of the Inner Ear
Vol. 12 (2021), pp. 29–49More LessWe recognize sounds by analyzing their frequency content. Different frequency components evoke distinct mechanical waves that each travel within the hearing organ, or cochlea, to a frequency-specific place. These signals are detected by hair cells, the ear's sensory receptors, in response to vibrations of mechanically sensitive antennas termed hair bundles. An active process enhances the sensitivity, sharpens the frequency tuning, and broadens the dynamic range of hair cells through several mechanisms, including active hair-bundle motility. A dynamic interplay between negative stiffness mediated by ion channels’ gating forces and delayed force feedback owing to myosin motors and channel reclosure by calcium ions brings the hair bundle to the vicinity of an oscillatory instability—a Hopf bifurcation. Operation near a Hopf bifurcation provides nonlinear generic features that are characteristic of hearing. Multiple gradients at molecular, cellular, and supercellular scales tune hair cells to characteristic frequencies that cover our auditory range.
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On the Role of Competing Interactions in Charged Colloids with Short-Range Attraction
Vol. 12 (2021), pp. 51–70More LessIn this review, we discuss recent advances in the investigation of colloidal systems interacting via a combination of short-range attraction and long-range repulsion. The prototypical examples of this phenomenology are charged colloids with depletion interactions, but the results apply, to a large extent, also to suspensions of globular proteins, clays, and, in general, to systems with competing attractive (hydrophobic) and repulsive (polar) contributions. After a brief introduction to the problem, we focus on the three disordered states that characterize these systems: equilibrium cluster phase, equilibrium gel, and Wigner glass of clusters. We provide a comparison of their static and dynamic observables, mainly by means of numerical simulations. Next, we discuss the few available studies on their viscoelastic properties and on their response to an external shear. Finally, we provide a summary of the current findings and also raise the main open questions and challenges for the future in this topic.
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The Fracture of Highly Deformable Soft Materials: A Tale of Two Length Scales
Vol. 12 (2021), pp. 71–94More LessThe fracture of highly deformable soft materials is of great practical importance in a wide range of technological applications, emerging in fields such as soft robotics, stretchable electronics, and tissue engineering. From a basic physics perspective, the failure of these materials poses fundamental challenges due to the strongly nonlinear and dissipative deformation involved. In this review, we discuss the physics of cracks in soft materials and highlight two length scales that characterize the strongly nonlinear elastic and dissipation zones near crack tips in such materials. We discuss physical processes, theoretical concepts, and mathematical results that elucidate the nature of the two length scales and show that the two length scales can classify a wide range of materials. The emerging multiscale physical picture outlines the theoretical ingredients required for the development of predictive theories of the fracture of soft materials. We conclude by listing open challenges and directions for future investigations.
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Modeling Grain Boundaries in Polycrystalline Halide Perovskite Solar Cells
Ji-Sang Park, and Aron WalshVol. 12 (2021), pp. 95–109More LessSolar cells are semiconductor devices that generate electricity through charge generation upon illumination. For optimal device efficiency, the photogenerated carriers must reach the electrical contact layers before they recombine. A deep understanding of the recombination process and transport behavior is essential to design better devices. Halide perovskite solar cells are commonly made of a polycrystalline absorber layer, but there is no consensus on the nature and role of grain boundaries. This review concerns theoretical approaches for the investigation of extended defects. We introduce recent computational studies on grain boundaries, and their influence on point-defect distributions, in halide perovskite solar cells. We conclude with a discussion of future research directions.
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Creep Motion of Elastic Interfaces Driven in a Disordered Landscape
Vol. 12 (2021), pp. 111–134More LessThe thermally activated creep motion of an elastic interface weakly driven on a disordered landscape is one of the best examples of glassy universal dynamics. Its understanding has evolved over the past 30 years thanks to a fruitful interplay among elegant scaling arguments, sophisticated analytical calculations, efficient optimization algorithms, and creative experiments. In this article, starting from the pioneer arguments, we review the main theoretical and experimental results that lead to the current physical picture of the creep regime. In particular, we discuss recent works unveiling the collective nature of such ultraslow motion in terms of elementary activated events. We show that these events control the mean velocity of the interface and cluster into “creep avalanches” statistically similar to the deterministic avalanches observed at the depinning critical threshold. The associated spatiotemporal patterns of activated events have been recently observed in experiments with magnetic domain walls. The emergent physical picture is expected to be relevant for a large family of disordered systems presenting thermally activated dynamics.
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Stem Cell Populations as Self-Renewing Many-Particle Systems
Vol. 12 (2021), pp. 135–153More LessThis article reviews the physical principles of stem cell populations as active many-particle systems that are able to self-renew, control their density, and recover from depletion. We illustrate the dynamical and statistical hallmarks of homeostatic mechanisms, from stem cell density fluctuations and transient large-scale oscillation dynamics during recovery to the scaling behavior of clonal dynamics and front-like boundary propagation during regeneration.
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Polyelectrolyte Complex Coacervates: Recent Developments and New Frontiers
Vol. 12 (2021), pp. 155–176More LessPolyelectrolyte complex coacervates represent a wide class of materials with applications ranging from coatings and adhesives to pharmaceutical technologies. They also underpin multiple biological processes, which are only now beginning to be deciphered. The means by which molecular-scale architecture propagates into macroscopic structure, thermodynamics, and dynamics in complex coacervates is of central concern in physics, chemistry, biology, and materials science. How does polyion charge sequence dictate thermodynamic behavior? How does one tailor rheology or interfacial tension using macromolecular architecture? What emergent functionality from polymer complex coacervates has biological consequences? Recent developments in coacervate science shed light on many of these issues and raise exciting new challenges for the close integration of theory, simulations, and experiment.
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Enzymes as Active Matter
Vol. 12 (2021), pp. 177–200More LessNature has designed multifaceted cellular structures to support life. Cells contain a vast array of enzymes that collectively perform essential tasks by harnessing energy from chemical reactions. Despite the complexity, intra- and intercellular motility at low Reynolds numbers remain the epicenter of life. In the past decade, detailed investigations on enzymes that are freely dispersed in solution have revealed concentration-dependent enhanced diffusion and chemotactic behavior during catalysis. Theoretical calculations and simulations have determined the magnitude of the impulsive force per turnover; however, an unequivocal consensus regarding the mechanism of enhanced diffusion has not been reached. Furthermore, this mechanical force can be transferred from the active enzymes to inert particles or surrounding fluid, thereby providing a platform for the design of biomimetic systems. Understanding the factors governing enzyme motion would help us to understand organization principles for dissipative self-assembly and the fabrication of molecular machines. The purpose of this article is to review the different classes of enzyme motility and discuss the possible mechanisms as gleaned from experimental observations and theoretical modeling. Finally, we focus on the relevance of enzyme motion in biology and its role in future applications.
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Symmetry Breaking and Nonlinear Electric Transport in van der Waals Nanostructures
Vol. 12 (2021), pp. 201–223More LessThe recent development of artificially fabricated van der Waals nanostructures makes it possible to design and control the symmetry of solids and to find novel physical properties and related functionalities. A characteristic physical property reflecting such symmetry breaking is the nonlinear response, which is typically studied as the second harmonic generation of light, although studies have recently expanded to include various transport phenomena. An important aspect of nonlinear transport for modern condensed matter physics is that it is not only a unique functionality of noncentrosymmetric systems but also an emergent property reflecting underlying physics such as spin–orbit interaction, superconductivity, magnetism, and band geometry/topology.
In this article, we review the nonlinear electrical transport in noncentrosymmetric van der Waals nanostructures obtained by exfoliation, nano-structure fabrication, or the application of an electric field, in particular, nonreciprocal transport resulting from inversion symmetry breaking and the bulk photovoltaic effect in nanomaterials without conventional p-n junctions.
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Band Representations and Topological Quantum Chemistry
Vol. 12 (2021), pp. 225–246More LessIn this article, we provide a pedagogical review of the theory of topological quantum chemistry and topological crystalline insulators. We begin with an overview of the properties of crystal symmetry groups in position and momentum space. Next, we introduce the concept of a band representation, which quantifies the symmetry of topologically trivial band structures. By combining band representations with symmetry constraints on the connectivity of bands in momentum space, we show how topologically nontrivial bands can be cataloged and classified. We present several examples of new topological phases discovered using this paradigm and conclude with an outlook toward future developments.
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Topology and Symmetry of Quantum Materials via Nonlinear Optical Responses
Vol. 12 (2021), pp. 247–272More LessWe review recent progress in the study of photogalvanic effects and optical second-harmonic generation in topological and noncentrosymmetric metals.
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Organization and Self-Assembly Away from Equilibrium: Toward Thermodynamic Design Principles
Vol. 12 (2021), pp. 273–290More LessStudies of biological systems and materials, together with recent experimental and theoretical advances in colloidal and nanoscale materials, have shown how nonequilibrium forcing can be used to modulate organization in many novel ways. In this review, we focus on how an accounting of energy dissipation, using the tools of stochastic thermodynamics, can constrain and provide intuition for the correlations and configurations that emerge in a nonequilibrium process. We anticipate that the frameworks reviewed here can provide a starting point to address some of the unique phenomenology seen in biophysical systems and potentially replicate them in synthetic materials.
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