D. Z. Yao

Far infrared optical properties of the pyrochlore spin ice compound Dy2Ti2O7

Near normal incidence far infrared reflectivity spectra of [111] dysprosium titanate (Dy2Ti2O7) single crystal have been measured at different temperatures. Seven phonon modes (eight at low temperature) are identified at frequencies below 1000 cm−1. Optical conductivity spectra are obtained by fitting all the reflectivity spectra with the factorized form of the dielectric function. Both the Born effective charges and the static optical permittivity are found to increase with decreasing temperature. Moreover, phonon linewidth narrowing and a phonon mode shift with decreasing temperature are also observed, which may result from enhanced charge localization. The redshift of several low frequency modes is attributed to the spin–phonon coupling. All observed optical properties can be explained within the framework of the nearest neighbour ferromagnetic (FM) spin ice model.

Quantum size dependent optical nutation in a core-shell CdSe/ZnS quantum dot

Abstract The energy eigenvalues and eigenfunctions have been obtained for a core-shell CdSe/ZnS quantum dot structure under effective-mass approximation. The electric transition dipole moment is calculated for the 1s–2s electronic transition. The optical nutation signal of the transition of electrons has been calculated numerically based on optical Bloch equations. Particularly, we have investigated the quantum size, the cores radius and the shells thickness, dependent optical nutation. It is shown from calculation results that the optical nutation signal is sensitive to the size and structure change. And the reasons for the variation of the Rabi frequency have been discussed based on the theory of the quantum size confined effect (QSCE).

Electron–phonon coupling in Nb-doped SrTiO3 single crystal

Near normal incident infrared reflectivity spectra of (001) SrTi1−xNbxO3 single crystal have been measured at different temperatures in the frequency region between 100 and 6000 cm−1. The optical parameters of phonons and plasmons are obtained on the basis of the double-damping extended Drude model. The lowest frequency phonon mode at 175 cm−1 softens with decreasing temperature, and the plasmon frequency triples when the temperature decreases from 300 to 10 K. Extra absorption near the highest frequency longitudinal phonon mode shows that the effect of the polarons should be taken into account in addition to the plasmon–phonon coupling. The splitting of the last high reflectivity band, the temperature dependence of the 615 cm−1 structure and the appearance of a new weak peak-like defect mode provide evidence for the existence of small polarons.