Robert G. Wheeler

Optical Spectrum of Re4+ in Single Crystals of K2PtCl6 and Cs2ZrCl6 at 4.2°K

The optical spectrum of Re4+(5d3) has been studied at 4.2°K in single crystals of K2PtCl6 and Cs2ZrCl6. The spectrum is characterized by extremely narrow lines in the region from 8500 to 36 000 cm−1. Vibrational structure is observed which is assigned to the odd modes of the ReCl62− complex. A crystal‐field analysis of the 0–0 transitions fits the observed eight electronic transitions with an rms deviation of 209 cm−1 for the parameters A = 0, B = 327 cm−1, C = 1818 cm−1, V = 30 347 cm−1, and λ5d=2392 cm−1. Magnetic‐field measurements of the excited states give g values which are compared with theory. A discussion of the intensities of the transitions is presented which demonstrates that some absorptions observed are magnetic‐dipole transitions. Finally, several conclusions about the study of optical spectra of dn systems are presented.

Electron-phonon scattering rates in GaAs/AlGaAs 2DEG samples below 0.5 K

We have studied electron heating in a 2DEG in GaAs/AlGaAs heterojunctions below 0.5 K. The electron temperature was raised above the lattice temperature using Joule heating. Weak localization and the temperature-dependent sample resistance were used as thermometers for the electrons. The electron-phonon energy relaxation rate was found to be proportional to T 3 . We find that the relaxation rate increases with disorder in the system.

Electron temperature and thermal conductance of GaAs 2D electron gas samples below 0.5 K

Abstract The electron phase coherence length is used as a thermometer to measure the temperature of a 2DEG. We find that the electron temperature differs from the mixing chamber temperature of the refrigerator by as much as 100 mK at base temperature. We also measure the thermal resistance between the electron gas and the mixing chamber and find a resistance comparable to that predicted by the Wiedemann-Franz law for the electron gas alone. Our results indicate an extraneous power level of about 4 pW in our experimental configuration.

The influence of impurities on inter-Landau-level equilibration

Abstract Strong, reproducible fluctuations are observed in the inter-Landau-level scattering rate as the depletion potential along the edge of a Hall conductor is varied using gate electrodes. The fluctuations are thought to be due to the changing influence of immobile impurity atoms on the scattering rate. A scattering length is extracted from the data, and its inverse is found to have a linear temperature dependence. This suggests that an activated hopping model, which predicts an exponential temperature dependence, is not applicable.