Observation of Metastable and Stable Energy Levels of EL2 in Semi-insulating GaAs

By using combination of detailed experimental studies, we identify the metastable and stable energy levels of EL2 in semi-insulating GaAs. These results are discussed in the light of the recently proposed models for stable and metastable configurations of EL2 in GaAs

Splitting between quadrupole modes of dilute quantum gas in a two dimensional anisotropic trap

We consider quadrupole excitations of quasi-two dimensional interacting quantum gas in an anisotropic harmonic oscillator potential at zero temperature. Using the time-dependent variational approach, we calculate a few low-lying collective excitation frequencies of a two dimensional anisotropic Bose gas. Within the energy weighted sum-rule approach, we derive a general dispersion relation of two quadrupole excitations of a two dimensional deformed trapped quantum gas. This dispersion relation is valid for both statistics. We show that the quadrupole excitation frequencies obtained from both methods are exactly the same. Using this general dispersion relation, we also calculate the quadrupole frequencies of a two dimensional unpolarized Fermi gas in an anisotropic trap. For both cases, we obtain analytic expressions for the quadrupole frequencies and the splitting between them for arbitrary value of trap deformation. This splitting decreases with increasing interaction strength for both statistics. For two dimensional anisotropic Fermi gas, the two quadrupole frequencies and the splitting between them become independent of the particle number within the Thomas-Fermi approach.Comment: 8 pages, 3 ps figs, to appear in The European Physical Journal