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The terahertz dielectric response of LuFe2O4 is investigated by terahertz time-domain spectroscopy over a temperature range of 6–290 K. It is revealed that besides the central mode associated with the charge-ordered state, a soft TO1 mode at below ∼240 K is identified indicating the existence of displacing ferroelectricity, in addition to the charge-ordering-induced ferroelectricity at below 320 K. The anomaly of the soft mode at ∼180 K reflects the magnetoelectric correlation between the soft TO1 mode and the spin/charge fluctuations revealed recently. Finally, the magnetic property at below ∼240 K is discussed. [ABSTRACT FROM AUTHOR]

Superconductor is a compelling plasmonic medium at terahertz frequencies owing to its intrinsic low Ohmic loss and good tuning property. However, the microscopic physics of the interaction between terahertz wave and superconducting plasmonic structures is still unknown. In this paper, we conducted experiments of the enhanced terahertz transmission through a series of superconducting NbN subwavelength hole arrays, and employed microscopic hybrid wave model in theoretical analysis of the role of hybrid waves in the enhanced transmission. The theoretical calculation provided a good match of experimental data. In particular, we obtained the following results. When the width of the holes is far below wavelength, the enhanced transmission is mainly caused by localized resonance around individual holes. On the contrary, when the holes are large, hybrid waves scattered by the array of holes dominate the extraordinary transmission. The surface plasmon polaritions are proved to be launched on the surface of superconducting film and the excitation efficiency increases when the temperature approaches critical temperature and the working frequency goes near energy gap frequency. This work will enrich our knowledge on the microscopic physics of extraordinary optical transmission at terahertz frequencies and contribute to developing terahertz plasmonic devices. [ABSTRACT FROM AUTHOR]

The terahertz dielectric response of LuFe2O4 is investigated by terahertz time-domain spectroscopy over a temperature range of 6–290 K. It is revealed that besides the central mode associated with the charge-ordered state, a soft TO1 mode at below ∼240 K is identified indicating the existence of displacing ferroelectricity, in addition to the charge-ordering-induced ferroelectricity at below 320 K. The anomaly of the soft mode at ∼180 K reflects the magnetoelectric correlation between the soft TO1 mode and the spin/charge fluctuations revealed recently. Finally, the magnetic property at below ∼240 K is discussed. [ABSTRACT FROM AUTHOR]