The interaction between light and matter is one of the main sources of information about the physical properties of the world around us. The way the electrons and nuclei interact with electromagnetic waves of different wavelengths reflects their microscopic self-organization in the materials. In particular, their collective modes, such as plasma waves of electrons, lattice vibrations and excitonic (interband) transitions, make specific imprints in the terahertz, infrared and visible spectra, which, when deciphered, provide invaluable scientific insights and clues for new applications.
It is extremely important to understand the material properties at the nanoscale. However, the Abbe’s principle limits the resolution in optical microscopy to about one-half of the wavelength when the light source is located by more that one wavelength from the studied object (far-field illumination). This ‘malediction’ can be removed using near-field optical methods, which already exist for many decades but have only recently become mature enough to be routinely used in the fundamental material research. In particular, the method of scattering-type scanning near-field optical microscopy (s-SNOM), which combines the atomic-force microscopy (AFM) with optical illumination, has demonstrated a wavelength-independent spatial resolution of about 10 nanometers in an extremely broad spectral range from the terahertz to the visible.
Our group conducts infrared optical studies of functional oxides and 2D van der Waals materials, which present significant interest for optoelectronic and plasmonic applications. We use a combination of near-field and far-field techniques under variable temperature with a possibility to apply external magnetic field and electrostatic gating. A central and most unique piece of our instrumentation is a cryogenic s-SNOM system (Neaspec GmbH) equipped with several tunable monochromatic and broadband laser sources covering the wavelength range between 5 and 17 microns (photon energies between 73 – 310 meV). This instrument allows us to perform infrared nanoscopy at temperatures down to 6 K, using closed-cycle cooling. Additionally, we use a conventional FT-IR microscope (Bruker Optics) equipped with optical and magneto-optical cryostats. All studies are done in a close collaboration with other groups inside and outside the DQMP specialized in the crystal and thin-film growth, transport measurements, Raman spectroscopy and ARPES.
Our current research projects include:
- electromagnetic properties of two-dimensional electron gas (2DEG) formed at oxide interfaces
- electronic phase separation at metal-insulator transitions in transition-metal oxides
- electrically tunable surface phonon-polaritons (PhPs) in functional oxides and van der Waals materials
- magneto-plasmons in graphene
- quantitative methods spectral modelling in the near-field and far-field experiments.