This review summarizes recent developments in the theory of spin glasses, as well as pertinent experimental data. The most characteristic properties of spin glass systems are described, and related phenomena in other glassy systems (dielectric and orientational glasses) are mentioned. The Edwards-Anderson model of spin glasses and its treatment within the replica method and mean-field theory are outlined, and concepts such as "frustration," "broken replica symmetry," "broken ergodicity," etc., are discussed. The dynamic approach to describing the spin glass transition is emphasized. Monte Carlo simulations of spin glasses and the insight gained by them are described. Other topics discussed include site-disorder models, phenomenological theories for the frozen phase and its excitations, phase diagrams in which spin glass order and ferromagnetism or antiferromagnetism compete, the Ne\'el model of superparamagnetism and related approaches, and possible connections between spin glasses and other topics in the theory of disordered condensed-matter systems.

Spin glasses: Experimental facts, theoretical concepts, and open questions

Unlike silver and gold, aluminum has material properties that enable strong plasmon resonances spanning much of the visible region of the spectrum and into the ultraviolet. This extended response, combined with its natural abundance, low cost, and amenability to manufacturing processes, makes aluminum a highly promising material for commercial applications. Fabricating Al-based nanostructures whose optical properties correspond with theoretical predictions, however, can be a challenge. In this work, the Al plasmon resonance is observed to be remarkably sensitive to the presence of oxide within the metal. For Al nanodisks, we observe that the energy of the plasmon resonance is determined by, and serves as an optical reporter of, the percentage of oxide present within the Al. This understanding paves the way toward the use of aluminum as a low-cost plasmonic material with properties and potential applications similar to those of the coinage metals.

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Aluminum for Plasmonics

Time-resolved, pulsed terahertz spectroscopy has developed into a powerful tool to study charge carrier dynamics in semiconductors and semiconductor structures over the past decades. Covering the energy range from a few to about 100 meV, terahertz radiation is sensitive to the response of charge quasiparticles, e.g., free carriers, polarons, and excitons. The distinct spectral signatures of these different quasiparticles in the THz range allow their discrimination and characterization using pulsed THz radiation. This frequency region is also well suited for the study of phonon resonances and intraband transitions in low-dimensional systems. Moreover, using a pump-probe scheme, it is possible to monitor the nonequilibrium time evolution of carriers and low-energy excitations with sub-ps time resolution. Being an all-optical technique, terahertz time-domain spectroscopy is contact-free and noninvasive and hence suited to probe the conductivity of, particularly, nanostructured materials that are difficult or impossible to access with other methods. The latest developments in the application of terahertz time-domain spectroscopy to bulk and nanostructured semiconductors are reviewed.

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Carrier dynamics in semiconductors studied with time-resolved terahertz spectroscopy

The physics of one-dimensional interacting bosonic systems is reviewed. Beginning with results from exactly solvable models and computational approaches, the concept of bosonic Tomonaga-Luttinger liquids relevant for one-dimensional Bose fluids is introduced, and compared with Bose-Einstein condensates existing in dimensions higher than one. The effects of various perturbations on the Tomonaga-Luttinger liquid state are discussed as well as extensions to multicomponent and out of equilibrium situations. Finally, the experimental systems that can be described in terms of models of interacting bosons in one dimension are discussed.

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One dimensional bosons: From condensed matter systems to ultracold gases

We present an ultrabroadband thin-film infrared absorber made of sawtoothed anisotropic metamaterial. Absorptivity of higher than 95% at normal incidence is supported in a wide range of frequencies, where the full absorption width at half-maximum is about 86%. Such property is retained well at a very wide range of incident angles too. Light of shorter wavelengths are harvested at upper parts of the sawteeth of smaller widths, while light of longer wavelengths are trapped at lower parts of larger tooth widths. This phenomenon is explained by the slowlight modes in anisotropic metamaterial waveguide. Our study can be applied in the field of designing photovoltaic devices and thermal emitters.

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Ultrabroadband light absorption by a sawtooth anisotropic metamaterial slab

1. Essentials 1.1 Lorentz field 1.2 Clausius-Mossotti 1.3 Maxwell-Garnett 1.4 Bruggeman 1.5 Green's functions formulation 1.6 Summary and equivalence 2. Rigorous results 2.1 Introduction 2.2 Variational bounds 2.3 The concentric shell model 2.4 Spectral representation 2.5 Exactly soluble models 2.6 Reciprocity theorems 3. Dynamical theory 3.1 Introduction 3.2 Review 3.3 Macroscopic electrodynamics 3.4 Quasi-static regime 3.5 Displacement current and wave scattering 3.6 Mie scattering 3.7 Dynamical effective medium theory 3.8 Open problems 4. Limitations and beyond 4.1 Introductory remarks 4.2 Higher order terms 4.3 Percolation and criticality 4.4 Mie resonances 4.5 Multiple scattering 4.6 Competing interactions 4.7 Two body effective medium 4.8 Non-equilibrium 5. Related theories 5.1 Comments 5.2 Coherent potential approximation 5.3 Feynman diagrams 5.4 Localization of light 5.5 Classical theory of liquids 5.6 Density functional theories 5.7 Hubbard model, CPA and DFT 5.8 Summary 6. EMT applications 6.1 Introduction 6.2 Electric and magnetic properties 6.3 Optical properties 6.4 Granular high Tc superconductors 6.5 Hydrodynamics of suspensions 6.6 Mechanical properties 6.7 Nonlinear composites 6.8 Conclusions Appendices A.1 Stationery properties of UP and UR A.2 Evaluation of the last term in equation (2.18)

Effective medium theory : principles and applications

Failure of Bethe-Ansatz solutions of generalisations of the Hubbard chain to arbitrary permutation symmetry

Density of states for a two-dimensional Penrose lattice: Evidence of a strong Van-Hove singularity.

We conclude our investigations of the local magnetic field distributions P(h) by examining disordered spin systems. Exact analytical results are given on the Bethe lattice with random bonds and the Sherrington-Kirkpatrick (SK) spin-glass model. Below the spin-glass transition temperature ${T}_{g}$ of the SK model, the slope of P(0) as a function of temperature is found to be almost linear, frozen to its value at ${T}_{g}$, in a manner reminiscent of other freezing phenomena found for this model. Simulations on finite-range models appear to show a correlated onset of certain features characteristic of the spin-glass phase of the SK (infinite-range) model but at a temperature higher than any associated with a phase transition.

T. C. Choy

Papers

Effective medium theory : principles and applications

Failure of Bethe-Ansatz solutions of generalisations of the Hubbard chain to arbitrary permutation symmetry

Density of states for a two-dimensional Penrose lattice: Evidence of a strong Van-Hove singularity.

Local magnetic field distributions. III. Disordered systems

Some exact results for a degenerate Hubbard model in one dimension