Ultrafast spectroscopy in high magnetic fields (Presentation Recording)

Two-dimensional systems offer a rich array of physical phenomena that include the integer and fractional quantum Hall effects, both of which have been observed in multiple materials systems to date. The mitigation and control of coherence in quantum states in 2D systems is an area of great current interest that is critical for the development of the next generation of solid state electronics based on quantum phenomena. In the first experiments that I will discuss, we investigate the terahertz frequency properties of a high mobility (μ ≥ 106 cm2 V-1 s-1) gallium arsenide two-dimensional electron gas (2DEG) at cyclotron resonance in a perpendicular magnetic field, which results in the formation of a spectrum of Landau levels. Our experiments reveal a strong increase in the decoherence at low temperatures and a power law dependence to the decoherence time from T = 0.4 - 100 K. In the second part of the talk, I will discuss our high fluence, nondegenerate pump-probe spectroscopic experiments of GaAs in the Florida Split Helix magnet at 15 K and 25 T. We model the electronic component of our data with an approximate four level system, from which we have extracted scattering and recombination rates in high magnetic field. We also observe coherent phonons, which were isolated and fitted to a sinusoid with an oscillation frequency of 43.5 GHz at 25 T, which is 3.0% larger than the previously measured zero field frequency.