In this paper, a two-dimensional square photonic crystal sPCd with superconductor cylinders is proposed to realize tunable negative refraction. Based on the dependence of the superconductors' permittivity on temperatures, photonic band structures thus negative refraction could be tuned by temperatures, whereby the refractive angle could be scanned from positive to negative. The feasibility of the PC operating in infrared and visible regions was discussed. The tunability resulted from the lattice, superconductors, operating frequency, and incident angle may lead the PC to great promise in photoelectronics and superconductor electronic applications.

The phonon-polariton dispersion relation is calculated in the piezoelectric superlattice (PSL). In this specific case, the coupling could take place not only between the electromagnetic (EM) waves (photons) and the transverse superlattice vibrations (transverse phonons), but also between the EM waves and the longitudinal superlattice vibrations (longitudinal phonons), which gives rise to two types of phonon polaritons. It differs with the case in an ionic crystal, where the phonon polariton could only originate from the coupling between transverse lattice vibrations (transverse optical phonons) and EM waves. The two types of phonon polaritons are experimentally observed in the one-dimensional PSL with a periodicity of micrometer scale, corresponding to the frequency region of microwave. The PSL is based on a congruent lithium tantalite (LiTaO3) crystal and fabricated by the method of electric field poling at room temperature. Both microwave absorption and dielectric abnormality are observed and the sizes of band gaps are measured for the two types of phonon polaritons.

Phonon-polaritons are studied both theoretically and experimentally in a one-dimensional two-component generalized quasiperiodic piezoelectric superlattice. The experimental observation of phonon-polaritons through dielectric abnormality is carried out at the microwave region. Some potential applications are discussed.

Single-phase insulating BiFeO3 ceramics have been synthesized by a simple but effective method that conventional solid state reaction is followed immediately by quenching processing. At room temperature, the ceramics show a metastable, distorted rhombohedral phase and the refined structure parameters are presented based on x-ray diffraction. It is revealed that the formations of Fe2+ and oxygen deficiency are greatly suppressed by the quenching processing. Awell-saturated ferroelectric hysteresis loop with a large remnant polarization (2Pr=23.5μC/cm2) is observed with an applied field of 155kV/cm. Temperature-dependent magnetic property is investigated and weak ferromagnetism with a remnant magnetization of 4×10−6μB/Fe at 10K is established. These results may have implications for further studies on multiferroics.

To realize the hole-mediated ferromagnetism, manganese and nitrogen-codoped ZnO(Zn1-xMnxO:N) films were prepared on sapphire (0001) by reactive radio-frequency (rf) magnetron sputtering from Zn0.97Mn0.03O ceramic targets using N2 gas. X-ray photon spectra reveal that the doped Mn ions are mainly in divalent states and the coexistence of O-Zn and N-Zn bonds in the films. According to the absorption spectra, the band gap of Zn0.97Mn0.03O: N films is about 3.15eV, which is slightly lower than that of ZnO films (3.20eV). Compared with Zn0.97Mn0.03O films, ferromagnetic behavior of Zn0.97Mn0.03O: N films were significantly changed with a coercivity of about 70 Oe, a saturation magnetization of 0.92μB/Mn2) and a remanance over 0.15μB/Mn2) at 300K, while at 10K, they increased to be about 110 Oe, 1.05μB/Mn2) and 0.23μB/Mn2), respectively. However, rapid thermal annealing treatment in pure oxygen results in a significant decrease on the magnetic properties of the films.