THz science and technology
Electromagnon in the Y-type hexaferrite BaSrCoZnFe11AlO22
We investigated static and dynamic magnetoelectric properties of single crystalline BaSrCoZnFe11AlO22 which is a room-temperature multiferroic with Y-type hexaferrite crystal structure. THz and Raman spectra reveal an electrically active spin wave (electromagnon) below 300 K at ≈1.2 THz. We show that the electromagnon is activated due to the magnetostriction mechanism involving spin vibrations along the hexagonal axis.
Departure from BCS response in photo-excited superconducting NbN films observed by terahertz spectroscopy
Ultrashort laser pulses can be used to induce transient exotic states of matter and cause phenomena of a vital interest such as room temperature superconductivity. We have focused on the photo-induced dynamics in niobium nitride (NbN) thin films  under strong excitation.
Quantum theory of terahertz conductivity of semiconductor nanostructures
In collaboration with T. Ostatnický of Charles University we participated to the development of the first theory of the quantum conductivity describing the transport in the terahertz spectral range, which does not contain internal contradictions. We have shown that the broken translation symmetry of the nanostructures induces a broadband drift-diffusion current which must be explicitly taken into account.
Picosecond charge transport in rutile at high carrier densities studied by transient terahertz spectroscopy
In rutile the charge carriers form polarons with high effective mass owing to the strong electron-phonon coupling. In this paper we studied ultrafast terahertz photoconductivity in rutile under strong optical excitation.
Ultrafast photoconductivity in semiconductor nanostructures
Time-resolved terahertz spectroscopy provides a useful insight into charge carrier motion in nanostructured semiconductors: it provides a contact-free access to local response of charge carriers inside nanostructures averaged over macroscopic volume of a sample. This is a very pertinent quantity for many applications of disordered materials which still have a larger potential than perfectly aligned nanostructures.
Nonmagnetic microspheres with resonant magnetic response
Metamaterials are artificial resonant composite structures formed by common materials; however, the sizes of the resonators and the distances among them are much smaller than the targeted wavelength of the radiation. A proper choice of materials and of their arrangement can induce an unusual electromagnetic behavior. In this way, it is possible to conceive e.g. a medium with a negative refractive index (i.e. with simultaneously negative dielectric permittivity and magnetic permeability) allowing one to overcome the diffraction limit in the optical imaging.