Physics Reports最新文献

In the past few decades, numerous heat conduction models extending beyond Fourier’s have been developed to account for large gradients, fast phenomena, wave propagation, and heterogeneous material structures typical of biological systems, superlattices, and thermal metamaterials. Navigating through these models has become challenging due to their varying thermodynamic backgrounds and potential compatibility issues. Furthermore, recent discoveries in the field of non-Fourier heat conduction have complicated the interpretation and utilization of specific non-Fourier heat equations, especially when designing materials for the new generation of thermal metamaterials. The situation is further compounded by the existence of numerous modeling strategies in the literature, each offering different interpretations of even the same heat equation. This complexity makes it increasingly difficult to gain a comprehensive understanding of this research field. Therefore, this review aims to facilitate the navigation of advanced heat equations beyond Fourier by discussing their properties and potential practical applications in the context of experiments. We begin with the simplest models and their fundamental principles, progressing toward more complex, coupled phenomena, such as ballistic heat conduction.

We do not delve into the often intricate technical details of each thermodynamic framework or aim to compare each approach from a methodological perspective. Instead, we focus on reviewing models primarily from the Rational Extended Thermodynamics, Extended Irreversible Thermodynamics, and Non-Equilibrium Thermodynamics with Internal Variables frameworks. Additionally, we discuss relevant models from kinetic theory, fractional derivatives, thermomass, and phase lag approaches. We provide background information on these models to highlight their origins, any limitations they may have, and the corresponding stability conditions, if applicable. Furthermore, as the field of non-Fourier heat conduction has become quite segmented, this paper also seeks to establish a common foundation, promoting a comprehensive mutual understanding of the fundamentals of each model and the phenomena to which they can be applied.

Physics is a field of science that has traditionally used the scientific method to answer questions about why natural phenomena occur and to make testable models that explain the phenomena. Discovering equations, laws, and principles that are invariant, robust, and causal has been fundamental in physical sciences throughout the centuries. Discoveries emerge from observing the world and, when possible, performing interventions on the system under study. With the advent of big data and data-driven methods, the fields of causal and equation discovery have developed and accelerated progress in computer science, physics, statistics, philosophy, and many applied fields. This paper reviews the concepts, methods, and relevant works on causal and equation discovery in the broad field of physics and outlines the most important challenges and promising future lines of research. We also provide a taxonomy for data-driven causal and equation discovery, point out connections, and showcase comprehensive case studies in Earth and climate sciences, fluid dynamics and mechanics, and the neurosciences. This review demonstrates that discovering fundamental laws and causal relations by observing natural phenomena is revolutionised with the efficient exploitation of observational data and simulations, modern machine learning algorithms and the combination with domain knowledge. Exciting times are ahead with many challenges and opportunities to improve our understanding of complex systems.

Nanotherapies are gaining increased interest for the treatment diverse diseases, particularly cancer, since they target the affected area directly, presenting higher efficacy and reduced side effects than traditional therapies. A promising nanotherapy approach is hyperthermia, where the nanoparticle can induce a local temperature increase by an external stimulus in the sick tissue to selectively kill the malignant cells. Among the diverse hyperthermia methods, photothermia is based on the absorption of light by the nanoparticles and further conversion into heat. Within the very wide range of nanostructured photothermal agents, iron oxides offer remarkable features since they are already approved by the FDA/EMA for various biomedical applications, they are biodegradable, easily manipulated using magnetic fields and can be imaged by diverse techniques. Here, we summarize the advantages of using the second biological window, both from the perspective of the skin and the optical properties of iron oxides. Further, we review the photothermal performance of iron oxide nanoparticles in the first, second and third biological windows. Overall, the results show that, for different types of iron oxide nanoparticles (Fe₃O₄, $\gamma$-Fe₂O₃, wüstite-FeO), both the heating capacity (i.e., induced temperature increase) and the photothermal conversion efficiency, $\eta$, vary in a complex way with the light wavelength, depending critically on the measurement conditions and physiochemical properties of the materials. Despite the spread in the reported photothermal properties of iron oxides, Fe₃O₄ particles tend to perform better than their $\gamma$-Fe₂O${}_3$ counterparts, particularly in the second biological window. Interestingly, FeO, which has not been exploited so far from a photothermal perspective, shows very appealing absorption properties. Our preliminary studies using FeO/Fe₃O₄ core/shell nanoparticles evidence that they have excellent photothermal properties, outperforming Fe₃O₄ in both first and second biological windows. Finally, some applications beyond cancer treatment of iron oxide nanoparticles, exploiting the enhanced properties in the second spectral window, are discussed.

These lectures were given at the Weizmann Institute in the spring of 2019. They are intended to familiarize students with the nuts and bolts of the numerical bootstrap as efficiently as possible. After a brief review of the basics of conformal field theory in $d>2$ spacetime dimensions, we discuss how to compute conformal blocks, formulate the crossing equations as a semi-definite programming problem, solve this problem using SDPB on a personal computer, and interpret the results. We include worked examples for all steps, including bounds for 3d CFTs with $Z_2$ or $O\left(N\right)$ global symmetries. Each lecture includes a problem set, which culminate in a precise computation of the 3d Ising model critical exponents using the mixed correlator $Z_2$ bootstrap. A Mathematica file is included that transforms crossing equations into the proper input form for SDPB.

Cold atomic gases have become a paradigmatic system for exploring fundamental physics, which at the same time allows for applications in quantum technologies. The accelerating developments in the field have led to a highly advanced set of engineering techniques that, for example, can tune interactions, shape the external geometry, select among a large set of atomic species with different properties, or control the number of atoms. In particular, it is possible to operate in lower dimensions and drive atomic systems into the strongly correlated regime. In this review, we discuss recent advances in few-body cold atom systems confined in low dimensions from a theoretical viewpoint. We mainly focus on bosonic systems in one dimension and provide an introduction to the static properties before we review the state-of-the-art research into quantum dynamical processes stimulated by the presence of correlations. Besides discussing the fundamental physical phenomena arising in these systems, we also provide an overview of the calculational and numerical tools and methods that are commonly used, thus delivering a balanced and comprehensive overview of the field. We conclude by giving an outlook on possible future directions that are interesting to explore in these correlated systems.

Frustration in magnetic materials arising from competing exchange interactions can prevent the system from adopting long-range magnetic order and can instead lead to a diverse range of novel quantum and topological states with exotic quasiparticle excitations. Here, we review prominent examples of such states, including magnetically-disordered and extensively degenerate spin ices with emergent magnetic monopole excitations, highly-entangled quantum spin liquids with fractional spinon excitations, topological order, and emergent gauge fields, as well as complex particle-like topological spin textures known as skyrmions. We provide an overview of recent advances in the search for magnetically-disordered candidate materials on the three-dimensional pyrochlore lattice and two-dimensional triangular, kagome and honeycomb lattices, the latter with bond-dependent Kitaev interactions, and on lattices supporting topological magnetism. We highlight experimental signatures of these often elusive phenomena and single out the most suitable experimental techniques that can be used to detect them. Our review also aims at providing a comprehensive guide for designing and investigating novel frustrated magnetic materials, with the potential of addressing some important open questions in contemporary condensed matter physics.

One-dimensional chains are used as a fundamental model of condensed matter, and have constituted the starting point for key developments in nonlinear physics and complex systems. The pioneering work in this field was proposed by Fermi, Pasta, Ulam and Tsingou in the 50s in Los Alamos. An intense and fruitful mathematical and physical research followed during these last 70 years. Recently, a fresh look at the mechanisms at the route of thermalization of such systems has been provided through the lens of the Wave Turbulence approach. In this review, we give a critical summary of the results obtained in this framework. We also present a series of open problems and challenges that future work needs to address.

We review how lattice QCD can contribute to the prediction and the comprehension of tetraquarks, pentaquarks and related exotic hadrons such as hybrids, with at least one heavy quark. We include all families of exotic hadrons, except for the quarkless glueballs, and the hexaquarks which are related to nuclear physics.

Since the discovery of quarks and the development of the QCD theory, there has been a large interest in exotic hadrons, initiated by the tetraquark models developed by Jaffe in 1977. Lattice QCD, being a first principle approach to solve non-perturbative QCD, has been crucial not only to compute precise results, but also to motivate and inspire research in hadronic physics, with particular interest in exotic hadrons.

In the new millennium, this interest exploded with several experimental discoveries of tetraquark and pentaquark resonances with heavy quarks, starting with the $Z_c$ and $Z_b$. So far, lattice QCD has not yet been able to comprehend this $Z$ class of tetraquarks, and is developing new methods to determine their masses, decay widths and decay processes.

The interest in tetraquarks was also fuelled by the lattice QCD prediction of a second class of tetraquarks such as the $T_{bb}$, boundstates in the sense of having no strong decays. Very recently, the $T_{cc}$ tetraquark first predicted with quark models in 1982 by Richard et al, was observed experimentally. We expect the lattice QCD community will be able to explore this $T$ class of tetraquarks in more detail and with very precise results.

We report on all the different direct and indirect approaches that lattice QCD, so far with most focus on tetraquarks, has been employing to study exotic hadrons with at least one heavy quark. We also briefly review the experimental progress in observing tetraquarks and pentaquarks, and the basic theoretical paradigms of tetraquarks, including three different types of mechanisms (diquark, molecular and s pole), comparing them with the results of lattice QCD. We aim to show the journey of Lattice QCD in the exploration of these fascinating and subtle hadrons.

Jamming is a ubiquitous phenomenon that appears in many soft matter systems, including granular materials, foams, colloidal suspensions, emulsions, polymers, and cells — when jamming occurs, the system undergoes a transition from flow-like to solid-like states. Conventionally, the jamming transition occurs when the system reaches a threshold jamming density under isotropic compression, but recent studies reveal that jamming can also be induced by shear. Shear jamming has attracted much interest in the context of non-equilibrium phase transitions, mechanics and rheology of amorphous materials. Here we review the phenomenology of shear jamming and its related physics. We first describe basic observations obtained in experiments and simulations, and results from theories. Shear jamming is then demonstrated as a “bridge” that connects the rheology of athermal soft spheres and thermal hard spheres. Based on a generalized jamming phase diagram, a universal description is provided for shear jamming in frictionless and frictional systems. We further review the isostaticity and criticality of the shear jamming transition, and the elasticity of shear jammed solids. The broader relevance of shear jamming is discussed, including its relation to other phenomena such as shear hardening, dilatancy, fragility, and discrete shear thickening.

Raman spectroscopy, since its discovery in 1928, left millions of footprints touching almost all researchers coming from multidisciplinary research areas and has established itself as an extremely important analytical tool. In recent times, it also has exhibited capabilities to get information about non-traditional physical processes in a material at microscopic levels. For example, the manifestation of temperature/thermal effect on a Raman spectrum. Conventionally termed anharmonic effect has been widely explored in various materials using Raman spectroscopy in elemental semiconductors (Si, Ge), binary materials (GaAs, Si-Ge), two-dimensional layered materials (Graphene, MoS ₂, WS₂), and transition metal oxides (TiO ₂, Fe₂O₃). Anharmonic effects manifest themselves in terms of shift in Raman peak position and broadening in the Raman spectra as a consequence of change in phonon energy and lifetime respectively. A lot of studies are available for temperature dependent Raman spectra which followed the phonon annihilation theory of Balkanski, but there are some materials which do not follow the traditional anharmonic trend only, also show some nonlinear trend with temperature. Deviation from the anharmonic theory in various materials like graphene, heavily doped silicon, thin films and some complex materials raised due to various reasons such as band structure, doping concentration, thickness of the film, etc. which causes the electron–phonon interaction or inherent phase transition in the material. Temperature dependent nonlinear behavior of Raman spectra has been given a very less attention and requires a wide study. Although the materials which show divergence from Balkanski’s anharmonic theory, show the predominance of electron–phonon interaction but at certain temperature anharmonic effect also take part which also needs to be explored and summarized in a perspective framework. A detailed review of available work in this less touched area has been presented here so as to give a different approach to analyze the effect of thermal perturbations on Raman line-shape. A compilation of temperature dependent Raman study from different range of materials has been presented and any observed deviation from the well-known anharmonic theory has been highlighted and possible reason for such deviation has been provided.