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- Volume 14, 2023
Annual Review of Condensed Matter Physics - Volume 14, 2023
Volume 14, 2023
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A Journey Through Nonlinear Dynamics: The Case of Temperature Gradients
Vol. 14 (2023), pp. 1–19More LessThe overall effect of temperature gradients is stressed for the Earth's core and surface, but also for the Sun's surface. Using Rayleigh–Bénard convection in helium and mercury, we measured all of the scaling properties of the period-doubling cascade and quasiperiodicity. Hard turbulence scaling properties are presented in an experiment using helium gas at low temperature. A scaling law is measured and also an exponential distribution for temperature fluctuations is observed. We present a study of a Rayleigh–Bénard convection cell with an open top and a floater. One of the simplest limit cycles is observed for the floater position. It follows a model proposed by Wilson for continent motion. Using the Soret effect, we study how temperature differences lead to strong accumulation of DNA suspensions. Also using polyethylene glycol concentration gradients, we measured local DNA and RNA accumulation. Finally, using thermal convection, we build one of the smallest PCR machines.
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An Adventure into the World of Soft Matter
Vol. 14 (2023), pp. 21–33More LessSoft matter is a field of condensed matter physics that began to develop in France in the 1970s under the impulse of Pierre-Gilles de Gennes. I had the chance to participate in this adventure, and I describe in this article some of the memorable events. Soft matter is not only linked to physics but also to chemistry and biology, and working in this multidisciplinary field is quite stimulating. My particular expertise deals with liquid surfaces, an area that considerably expanded with the advent of miniaturization, i.e., when surfaces begin to matter. I was able to benefit from the French and European network systems, as well as from many interactions with young students and industrial partners. I show how these favorable conditions contributed to successes in my research.
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Floquet States in Open Quantum Systems
Vol. 14 (2023), pp. 35–56More LessIn Floquet engineering, periodic driving is used to realize novel phases of matter that are inaccessible in thermal equilibrium. For this purpose, the Floquet theory provides us a recipe for obtaining a static effective Hamiltonian. Although many existing works have treated closed systems, it is important to consider the effect of dissipation, which is ubiquitous in nature. Understanding the interplay of periodic driving and dissipation is a fundamental problem of nonequilibrium statistical physics that is receiving growing interest because of the fact that experimental advances have allowed us to engineer dissipation in a controllable manner. In this review, we give a detailed exposition on the formalism of quantum master equations for open Floquet systems and highlight recent work investigating whether equilibrium statistical mechanics applies to Floquet states.
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Generalized Symmetries in Condensed Matter
Vol. 14 (2023), pp. 57–82More LessRecent advances in our understanding of symmetry in quantum many-body systems offer the possibility of a generalized Landau paradigm that encompasses all equilibrium phases of matter. This is a brief and elementary review of some of these developments.
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Non-Hermitian Topological Phenomena: A Review
Vol. 14 (2023), pp. 83–107More LessThe past decades have witnessed an explosion of interest in topological materials, and a lot of mathematical concepts have been introduced in condensed matter physics. Among them, the bulk-boundary correspondence is the central topic in topological physics, which has inspired researchers to focus on boundary physics. Recently, the concepts of topological phases have been extended to non-Hermitian Hamiltonians, whose eigenvalues can be complex. Besides the topology, non-Hermiticity can also cause a boundary phenomenon called the non-Hermitian skin effect, which is an extreme sensitivity of the spectrum to the boundary condition. In this article, we review developments in non-Hermitian topological physics by focusing mainly on the boundary problem. As well as the competition between non-Hermitian and topological boundary phenomena, we discuss the topological nature inherent in non-Hermiticity itself.
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Modeling Active Colloids: From Active Brownian Particles to Hydrodynamic and Chemical Fields
Vol. 14 (2023), pp. 109–127More LessActive colloids are self-propelled particles moving in viscous fluids by consuming fuel from their surroundings. Here, we review the numerical and theoretical modeling of active colloids propelled by self-generated near-surface flows. We start with the generic model of an active Brownian particle taking into account potential forces and effective pairwise interaction, which include hydrodynamic and phoretic interactions. Also, the squirmer as a model microswimmer is introduced. We then discuss the explicit modeling of self-generated fluid flow and the full hydrodynamic-chemical coupling. Finally, we discuss recent advances in selected topics in which modeling of active colloids is used to study motion in crowded and complex environments, microrheology in active baths, active colloidal engines, adaptive responses of active colloids with the help of machine learning techniques, as well as effects of colloid and fluid inertia.
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Spin Seebeck Effect: Sensitive Probe for Elementary Excitation, Spin Correlation, Transport, Magnetic Order, and Domains in Solids
Vol. 14 (2023), pp. 129–151More LessThe spin Seebeck effect (SSE) refers to the generation of a spin current as a result of a temperature gradient in a magnetic material, which can be detected electrically via the inverse spin Hall effect in a metallic contact. Since the discovery of the SSE in 2008, intensive studies on the SSE have been conducted to elucidate its origin. SSEs appear in a wide range of magnetic materials including ferro-, ferri-, and antiferromagnets and also paramagnets with classical or quantum spin fluctuation. SSE voltage reflects fundamental properties of a magnet, such as elementary excitation, static magnetic order, spin correlation, and spin transport. In this article, we review recent progress on the SSE in various systems, with particular emphasis on its emerging role as a probe of these magnetic properties in solids. We also briefly discuss the recently discovered nuclear SSE.
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Superconductivity and Local Inversion-Symmetry Breaking
Vol. 14 (2023), pp. 153–172More LessInversion and time reversal are essential symmetries for the structure of Cooper pairs in superconductors. The loss of one or both leads to modifications to this structure and can change the properties of the superconducting phases in profound ways. Superconductivity in materials lacking inversion symmetry, or noncentrosymmetric materials, has become an important topic. These materials show unusual magnetic and magnetoelectric properties and can host topological superconductivity. Recently, crystal structures with local, but not global, inversion-symmetry breaking have attracted attention. Here, superconductivity can exhibit phenomena not naively expected in centrosymmetric materials. In this review, we first introduce the concept of locally noncentrosymmetric crystals and different material realizations. We then discuss consequences of such local symmetry breaking on the normal state electronic structure and the classification of superconducting order parameters. Finally, we review the expected and, in parts, already observed phenomenology of unconventional superconductivity and possible topological superconducting phases.
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Tensor Network Algorithms: A Route Map
Vol. 14 (2023), pp. 173–191More LessTensor networks provide extremely powerful tools for the study of complex classical and quantum many-body problems. Over the past two decades, the increment in the number of techniques and applications has been relentless, and especially the last ten years have seen an explosion of new ideas and results that may be overwhelming for the newcomer. This short review introduces the basic ideas, the best established methods, and some of the most significant algorithmic developments that are expanding the boundaries of the tensor network potential. The goal of this review is to help the reader not only appreciate the many possibilities offered by tensor networks but also find their way through state-of-the-art codes, their applicability, and some avenues of ongoing progress.
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Spatial and Temporal Organization of Chromatin at Small and Large Scales
Vol. 14 (2023), pp. 193–210More LessDNA molecules with a total length of two meters contain the genetic information in every cell in our body. To control access to the genes, to organize its spatial structure in the nucleus, and to duplicate and faithfully separate the genetic material, the cell makes use of sophisticated physical mechanisms. Base pair sequences multiplex various layers of information, chromatin remodelers mobilize nucleosomes via twist defects, loop extruders create a system of nonconcatenated rings to spatially organize chromatin, and biomolecular condensates concentrate proteins and nucleic acids in specialized membraneless compartments. In this review, we discuss the current state of understanding of some of these mechanisms that influence the organization of the genetic material in space and time.
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Dissecting Flux Balances to Measure Energetic Costs in Cell Biology: Techniques and Challenges
Vol. 14 (2023), pp. 211–235More LessLife is a nonequilibrium phenomenon: Metabolism provides a continuous supply of energy that drives nearly all cellular processes. However, very little is known about how much energy different cellular processes use, i.e., their energetic costs. The most direct experimental measurements of these costs involve modulating the activity of cellular processes and determining the resulting changes in energetic fluxes. In this review, we present a flux balance framework to aid in the design and interpretation of such experiments and discuss the challenges associated with measuring the relevant metabolic fluxes. We then describe selected techniques that enable measurement of these fluxes. Finally, we review prior experimental and theoretical work that has employed techniques from biochemistry and nonequilibrium physics to determine the energetic costs of cellular processes.
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Data-Driven Discovery of Robust Materials for Photocatalytic Energy Conversion
Vol. 14 (2023), pp. 237–259More LessThe solar–to–chemical energy conversion of Earth-abundant resources like water or greenhouse gas pollutants like CO2 promises an alternate energy source that is clean, renewable, and environmentally friendly. The eventual large-scale application of such photo-based energy conversion devices can be realized through the discovery of novel photocatalytic materials that are efficient, selective, and robust. In the past decade, the Materials Genome Initiative has led to a major leap in the development of materials databases, both computational and experimental. Hundreds of photocatalysts have recently been discovered for various chemical reactions, such as water splitting and carbon dioxide reduction, employing these databases and/or data informatics, machine learning, and high-throughput computational and experimental methods. In this article, we review these data-driven photocatalyst discoveries, emphasizing the methods and techniques developed in the last few years to determine the (photo)electrochemical stability of photocatalysts, leading to the discovery of photocatalysts that remain robust and durable under operational conditions.
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Fermiology of Topological Metals
Vol. 14 (2023), pp. 261–309More LessThe modern scope of fermiology encompasses not just the classical geometry of Fermi surfaces but also the geometry of quantum wave functions over the Fermi surface. This enlarged scope is motivated by the advent of topological metals—metals whose Fermi surfaces are characterized by a robustly nontrivial Berry phase. We review the extent to which topological metals can be diagnosed from magnetic-field-induced quantum oscillations of transport and thermodynamic quantities. A holistic analysis of the oscillatory wave form is proposed, in which different characteristics of the wave form (e.g., phase offset, high-harmonic amplitudes, temperature-dependent frequency) encode different aspects of a topologically nontrivial Fermi surface. Which characteristic to focus on depends on (a) the orientation of the magnetic field relative to certain crystallographic axes, (b) the symmetry class of the topological metal, and (c) the separation of Fermi-surface pockets in quasimomentum space. Closely proximate pockets arise when (1) spin–split pockets are nearly overlapping due to a weak spin–orbit force or when (2) two pockets touch at an isolated point, which can be a topological band-touching point or a saddlepoint in the energy-momentum dispersion. The emergence of a pseudospin degree of freedom (in case 1) and the implications of magnetic breakdown (in case 2) are reviewed, with emphasis on new aspects originating from the (nonabelian) Berry connection of the Fermi surface. Future extensions of topofermiology are suggested in the directions of interaction-induced Fermi-liquid instabilities and two-dimensional electron liquids.
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Physics of Human Crowds
Vol. 14 (2023), pp. 311–333More LessUnderstanding the behavior of human crowds is a key step toward a safer society and more livable cities. Despite the individual variability and will of single individuals, human crowds, from dilute to dense, invariably display a remarkable set of universal features and statistically reproducible behaviors. Here, we review ideas and recent progress in employing the language and tools from physics to develop a deeper understanding about the dynamics of pedestrians.
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Random Quantum Circuits
Vol. 14 (2023), pp. 335–379More LessQuantum circuits—built from local unitary gates and local measurements—are a new playground for quantum many-body physics and a tractable setting to explore universal collective phenomena far from equilibrium. These models have shed light on longstanding questions about thermalization and chaos, and on the underlying universal dynamics of quantum information and entanglement. In addition, such models generate new sets of questions and give rise to phenomena with no traditional analog, such as dynamical phase transitions in quantum systems that are monitored by an external observer. Quantum circuit dynamics is also topical in view of experimental progress in building digital quantum simulators that allow control of precisely these ingredients. Randomness in the circuit elements allows a high level of theoretical control, with a key theme being mappings between real-time quantum dynamics and effective classical lattice models or dynamical processes. Many of the universal phenomena that can be identified in this tractable setting apply to much wider classes of more structured many-body dynamics.
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Swimming in Complex Fluids
Vol. 14 (2023), pp. 381–415More LessWe review the literature on swimming in complex fluids. A classification is proposed by comparing the length- and timescales of a swimmer with those of nearby obstacles, interpreted broadly, extending from rigid or soft confining boundaries to molecules that confer the bulk fluid with complex stresses. A third dimension in the classification is the concentration of swimmers, which incorporates fluids whose complexity arises purely by the collective motion of swimming organisms. For each of the eight system types that we identify, we provide a background and describe modern research findings. Although some types have seen a great deal of attention for decades, others remain uncharted waters still open and awaiting exploration.
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Learning Without Neurons in Physical Systems
Vol. 14 (2023), pp. 417–441More LessLearning is traditionally studied in biological or computational systems. The power of learning frameworks in solving hard inverse problems provides an appealing case for the development of physical learning in which physical systems adopt desirable properties on their own without computational design. It was recently realized that large classes of physical systems can physically learn through local learning rules, autonomously adapting their parameters in response to observed examples of use. We review recent work in the emerging field of physical learning, describing theoretical and experimental advances in areas ranging from molecular self-assembly to flow networks and mechanical materials. Physical learning machines provide multiple practical advantages over computer designed ones, in particular by not requiring an accurate model of the system, and their ability to autonomously adapt to changing needs over time. As theoretical constructs, physical learning machines afford a novel perspective on how physical constraints modify abstract learning theory.
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Quantum Many-Body Scars: A Quasiparticle Perspective
Vol. 14 (2023), pp. 443–469More LessWeakly interacting quasiparticles play a central role in the low-energy description of many phases of quantum matter. At higher energies, however, quasiparticles cease to be well defined in generic many-body systems owing to a proliferation of decay channels. In this review, we discuss the phenomenon of quantum many-body scars, which can give rise to certain species of stable quasiparticles throughout the energy spectrum. This goes along with a set of unusual nonequilibrium phenomena including many-body revivals and nonthermal stationary states. We provide a pedagogical exposition of this physics via a simple yet comprehensive example, that of a spin-1 XY model. We place our discussion in the broader context of symmetry-based constructions of many-body scar states, projector embeddings, and Hilbert space fragmentation. We conclude with a summary of experimental progress and theoretical puzzles.
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Odd Viscosity and Odd Elasticity
Vol. 14 (2023), pp. 471–510More LessElasticity typically refers to a material's ability to store energy, whereas viscosity refers to a material's tendency to dissipate it. In this review, we discuss fluids and solids for which this is not the case. These materials display additional linear response coefficients known as odd viscosity and odd elasticity. We first introduce odd viscosity and odd elasticity from a continuum perspective, with an emphasis on their rich phenomenology, including transverse responses, modified dislocation dynamics, and topological waves. We then provide an overview of systems that display odd viscosity and odd elasticity. These systems range from quantum fluids and astrophysical gases to active and driven matter. Finally, we comment on microscopic mechanisms by which odd viscosity and odd elasticity arise.
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