Nonlinear Terahertz spectroscopy on Ga-doped Germanium in high magnetic fields using intense free-electron laser radiation
At HFML-FELIX, researchers exposed hole-doped Germanium to intense free-electron laser radiation and high magnetic fields up to 33T. By combining a high-field magnet and a free-electron laser they were able to simultaneously photo-ionize the Ga-dopants and observe cyclotron resonance of the photo-exited free holes. The used experimental technique and the results of their experiments demonstrate the exciting new possibilities for researching nonlinear magneto-optical processes in solids. The results have been published in Physical Review B (Editors' Suggestion).
The development of pulsed, high-intensity Terahertz (THz) free-electron lasers (FELs) has enabled the investigation of nonlinear phenomena in molecules and solids in the THz regime. To expand their potential, recently THz FELs were combined with high magnetic fields in some laboratories around the world. At HFML-FELIX, researchers used FLARE, a THz FEL, in combination with a 33 Tesla DC magnet to investigate photoionization and cyclotron resonance in the gallium-doped semiconductor germanium over a wide range of THz intensities.
They observed cyclotron resonance transitions of free holes in the magneto-transmission spectra of the semiconductor at low temperatures, using intense radiation with a photon energy much lower than the ionization energy of the Gallium dopants. The magneto-optical spectra are very sensitive to the intensity and frequency of the THz light, providing new insights about the actual ionization mechanism, the saturation of the cyclotron resonance transitions and the excitation of higher energy Landau levels. The spectroscopic technique used here offers an exciting perspective for researching nonlinear magneto-optical processes in solid state materials.
Nonlinear Terahertz transmission spectroscopy on Ga-doped germanium in high magnetic fields, Bence Bernáth, Papori Gogoi, Andrea Marchese, Dmytro Kamenskyi, Hans Engelkamp, Denis Arslanov, Britta Redlich, Peter C. M. Christianen and Jan C. Maan, Phys. Rev. B 105, 205204 (2022)