The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Review of the magnetocaloric effect in manganite materials

M Agnetocaloric M Aterials

In this work we consider the role of aperiodic order in different domains of science and technology from an interdisciplinary approach. To start with, we introduce some general classification schemes for aperiodic arrangements of matter. Afterwards, we review the main physical properties and possible applications of quasiperiodic crystals. Several conceptual links between quasiperiodic crystals and the hierarchical structure of biopolymers are then discussed in connection with the charge transfer properties of both biological and synthetic DNA chains. The widespread presence of Fibonacci numbers and the golden mean in different physical contexts is also discussed. Promising technological applications of aperiodic systems are finally reviewed by considering both current and potential applications. In particular, we analyse the capability of exploiting aperiodic order in the design of novel devices based on semiconductor heterostructures and dielectric multilayers.

https://iopscience.iop.org/article/10.1088/0034-4885/69/2/R03/pdf

The role of aperiodic order in science and technology

Theory of elementary excitations in quasiperiodic structures

The polycrystalline perovskitelike manganese oxides La1-xAxMnO\(_{3 + \delta }\) (A = Na, and K, 0.05 < x ≤ 0.20) have been fabricated by sol-gel technique. For all the compositions explored in this work, the average manganese oxidation state is practically constant, at 3.32 ± 0.02 for A = Na, and 3.40 ± 0.04 for A = K, respectively. A close relationship is confirmed to hold between the Curie temperature (Tc) and the bond distance of Mn-O. Results of magnetic measurements show that these materials can be utilized as suitable candidates for magnetic refrigerants with wide applied temperature span, for their significant entropy change and the easily tuned Curie temperature.

Structure, composition and magnetocaloric properties in polycrystalline La1-xAxMnO\(_{3 + \delta }\) (A = Na, K)

We present in this letter the observation of the optical resonant transmission of Thue-Morse (TM) dielectric multilayers. For the first time the frequency trifurcation feature has been experimentally demonstrated. This effect can be analogous to the electronic energy spectrum of a TM system, which has not yet been directly obtained in experiments. The resonant transmission originates from the positional correlation of the basic units in the TM system, and is sensitive to the modulation of optical thickness. The experimental results are in good agreement with the theoretical analysis.

Resonant transmission and frequency trifurcation of light waves in Thue-Morse dielectric multilayers

We report here the reflection of electromagnetic waves in self-similar Thue-Morse dielectric multilayers, which presents the features of multiple omnidirectional photonic bandgaps (PBGs). The number and the width of omnidirectional PBG depend on the ratio of the refraction indexes and the thicknesses of the dielectric materials. The theoretical result is partly verified by optical observation in Thue-Morse TiO2/SiO2 multilayers with visible and near-infrared light. Our investigations provide a new approach to achieve the omnidirectional reflection in multiple frequency ranges. With this progress, the application of dielectric reflection mirrors can be further widened.

https://iopscience.iop.org/article/10.1209/epl/i2004-10261-y/pdf

Omnidirectional reflection of electromagnetic waves on Thue-Morse dielectric multilayers

The electronic behaviors in quantum wires with serial stubs are studied. A general theory of quantum waveguide based on transfer matrix method is developed and is used to treat periodic stub structures, serial stub structures with a defect stub, and Fibonacci stub structures. A number of interesting physical properties in connection with electronic transmission, energy spectra, and charge density distributions in these structures, are found theoretically. In particular, we find that whether there are periodicity and symmetry in the transmission and energy spectra depends on the commensurability of the length parameters. If one length ratio is incommensurate, then the transmission and energy spectra do not exhibit periodicity and symmetry even for periodic stub structures. In particular, the quasiperiodic behaviors are shown in Fibonacci stub structures proposed by us whenever the length parameters are commensurate. The experimental relevance is also addressed briefly.

/pdf/quantum-waveguide-theory-of-serial-stub-structures-2us09rvcr4.pdf

Quantum waveguide theory of serial stub structures

A new class of quasiperiodic superlattice structures called three-component Fibonacci structures has been studied both theoretically and experimentally. These structures with the characteristic irrational intervals A, B, and C can be produced by the substitution rule A\ensuremath{\rightarrow}AC, C\ensuremath{\rightarrow}B, and B\ensuremath{\rightarrow}A. The projection method is applied to deal with the pattern and index of their diffraction spectrum. The analytical results are compared with the experimental one from three-component Fibonacci Ta/Al superlattices. The experimental results are in good agreement with the numerical calculations using the model for compositionally modulated multilayers. Some possible applications of these structures are discussed.

A. Hu

Papers

Structure, composition and magnetocaloric properties in polycrystalline La1-xAxMnO\(_{3 + \delta }\) (A = Na, K)

Resonant transmission and frequency trifurcation of light waves in Thue-Morse dielectric multilayers

Omnidirectional reflection of electromagnetic waves on Thue-Morse dielectric multilayers

Quantum waveguide theory of serial stub structures

Structural characterization of three-component Fibonacci Ta/Al multilayer films.