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

Modified gravity theories on a nutshell: Inflation, bounce and late-time evolution

This review discusses how low-energy, valence excitations created by swift electrons can render information on the optical response of structured materials with unmatched spatial resolution. Electron microscopes are capable of focusing electron beams on sub-nanometer spots and probing the target response either by analyzing electron energy losses or by detecting emitted radiation. Theoretical frameworks suited to calculate the probability of energy loss and light emission (cathodoluminescence) are revisited and compared with experimental results. More precisely, a quantum-mechanical description of the interaction between the electrons and the sample is discussed, followed by a powerful classical dielectric approach that can be in practice applied to more complex systems. We assess the conditions under which classical and quantum-mechanical formulations are equivalent. The excitation of collective modes such as plasmons is studied in bulk materials, planar surfaces, and nanoparticles. Light emission induced by the electrons is shown to constitute an excellent probe of plasmons, combining sub-nanometer resolution in the position of the electron beam with nanometer resolution in the emitted wavelength. Both electron energy-loss and cathodoluminescence spectroscopies performed in a scanning mode of operation yield snap shots of plasmon modes in nanostructures with fine spatial detail as compared to other existing imaging techniques, thus providing an ideal tool for nanophotonics studies.

/pdf/optical-excitations-in-electron-microscopy-3d2rfnfkst.pdf

Optical excitations in electron microscopy

Dynamics of Phononic Materials and Structures: Historical Origins, Recent Progress, and Future Outlook

The form of energy termed heat that typically derives from lattice vibrations, i.e., phonons, is usually considered as waste energy and, moreover, deleterious to information processing. However, in this Colloquium, an attempt is made to rebut this common view: By use of tailored models it is demonstrated that phonons can be manipulated similarly to electrons and photons, thus enabling controlled heat transport. Moreover, it is explained that phonons can be put to beneficial use to carry and process information. In the first part ways are presented to control heat transport and to process information for physical systems which are driven by a temperature bias. In particular, a toolkit of familiar electronic analogs for use of phononics is put forward, i.e., phononic devices are described which act as thermal diodes, thermal transistors, thermal logic gates, and thermal memories. These concepts are then put to work to transport, control, and rectify heat in physically realistic nanosystems by devising practical designs of hybrid nanostructures that permit the operation of functional phononic devices; the first experimental realizations are also reported. Next, richer possibilities to manipulate heat flow by use of time-varying thermal bath temperatures or various other external fields are discussed. These give rise to many intriguing phononic nonequilibrium phenomena such as, for example, the directed shuttling of heat, geometrical phase-induced heat pumping, or the phonon Hall effect, which may all find their way into operation with electronic analogs.

/pdf/colloquium-phononics-manipulating-heat-flow-with-electronic-3ofg34ywrl.pdf

Colloquium : Phononics: Manipulating heat flow with electronic analogs and beyond

Negative refraction of acoustic waves in two-dimensional phononic crystals has been demonstrated through both analysis and exact numerical simulation. The methods to achieve this behavior have been discussed. A microsuperlens for acoustic waves has also been designed. It is shown that refractive devices based on phononic crystals behave in a manner similar to that of optical systems. Therefore, a negative square root of the effective density or negative refraction index for acoustic waves can be introduced to describe this phenomena very well as the case of electromagnetic waves in the photonic crystals.

Negative refraction of acoustic waves in two-dimensional phononic crystals

It is shown, for the first time, that the Zitterbewegung of photons can appear near the Dirac point in a two-dimensional photonic crystal. The superiority of such a phenomenon for photons is that it can be found in different scaling structures with wide frequency regions. It can be observed by measuring the time dependence of the transmission coefficient through photonic crystal slabs. Thus, it is particularly suited for experimentally observing this effect. We have observed such a phenomenon by exact numerical simulations, confirming a long-standing theoretical prediction.

Observing Zitterbewegung for photons near the Dirac point of a two-dimensional photonic crystal.

This paper studies the transport properties of charge carriers through graphene superlattices consisting of monolayer or bilayer graphene on the basis of the transfer-matrix method. Emphasis is placed on the relationship between the Klein paradox and resonant tunneling in double-barrier junctions. It is shown that normal incidence transmission probabilities for two kinds of graphene structure exhibit different features. Independent of structure parameters, they are always perfectly transmitted in a monolayer graphene structure. In contrast, the transmission resonances occur in a bilayer graphene structure. However, the angularly averaged conductivities for both depend on the thickness and height of the barriers as well as the width and number of the well. That is to say, the angularly averaged conductivities in monolayer and bilayer graphene superlattices can be controlled by changing the structure parameters even if Klein tunneling exists.

Klein paradox and resonant tunneling in a graphene superlattice

Based on the two-band model, we present a transfer-matrix treatment of the tunnel conductance and magnetoresistance for tunneling through ferromagnet/insulator (semiconductor) single junctions and double junctions subject to a dc bias. Our results are qualitatively in agreement with the experimental measurements for the single junction. For the double junction, we find that there exists, spin-polarized resonant tunneling and giant tunnel magnetoresistance. The highest value of the magnetoresistance in a double junction can reach 90%. We anticipate that our results will stimulate some interest in experimental efforts in designing spin-polarized resonant-tunneling devices.

Spin-polarized tunneling and magnetoresistance in ferromagnet/insulator(semiconductor) single and double tunnel junctions subjected to an electric field

A recent publication [Nature (London) 404, 740 (2000)] claimed that absolute photonic gaps can be realized in 12-fold quasicrystalline arrangement of small airholes in a matrix of silicon nitride or glass. The result is rather surprising since silicon nitride $(n=2.02)$ and in particular, glass $(n=1.45)$ have rather low refractive index. In this work, we have studied the transmission properties of the same systems by using the multiple-scattering method. We found that the 12-fold triangle-square tiling is indeed very good for the realization of photonic gaps and we found absolute gaps in systems with airholes in dielectric, dielectric cylinders in air, and metal cylinders in air. However, for the case of air-holes in a dielectric background, absolute gaps appear only when the dielectric contrast is sufficiently high, and both silicon nitride and glass have refractive indices below the threshold.

/pdf/absolute-photonic-band-gaps-in-12-fold-symmetric-photonic-13c3xrpxyp.pdf

Xiangdong Zhang

Papers

Negative refraction of acoustic waves in two-dimensional phononic crystals

Observing Zitterbewegung for photons near the Dirac point of a two-dimensional photonic crystal.

Klein paradox and resonant tunneling in a graphene superlattice

Spin-polarized tunneling and magnetoresistance in ferromagnet/insulator(semiconductor) single and double tunnel junctions subjected to an electric field

Absolute photonic band gaps in 12-fold symmetric photonic quasicrystals