Raman Spectroscopy

General

Inelastic light scattering is a photon in-photon out process and was discovered simultaneously by Raman and Krishnan in liquids and by Landsberg and Mandelstam in quartz about 80 years ago. In these days it is a widely used tool in analytics and basis research. At the WMI Raman scattering is mainly used for the study of electronic properties of superconductors and highly correlated electron systems (link to RMP). In addition, fullerenes, carbon nanotubes, hydrogen, and provskites were investigated.

Generally, an incoming polarized photon is absorbed and another one with different energy, momentum, and polarization is emitted. In the course of the scattering process, an elementary excitation is created in the material with energy and momentum corresponding to the energy and momentum difference of the two photons. Since light can be scattered by molecular vibrations and rotations, lattice modes (phonons), conduction electrons, spin waves, and orbital excitations a host of information can be obtained. Due to the freedom to independently adjust the polarizations of two photons selection rules arise which are widely used for, e.g., the interpretation of vibrational or spin-wave spectra.

In the case of conduction electrons different areas of the Fermi surface can be accessed independently with appropriate combinations of photon polarizations. This allowed us to map out the energy gap in cuprate superconductors or to determine dynamic properties or normal electrons as a function of momentum hence providing information beyond conventional infrared (optical) spectroscopy.