Fractional charges and quantum phase transitions in imbalanced bilayer quantum Hall systems

We extend the Composite Boson theory to study slightly im-balanced bi-layer Quantum Hall systems. In the global $U(1)$ symmetry breaking excitonic superfluid side, as the imbalance increases, the system supports continuously changing fractional charges. In the translational symmetry breaking pseudo-spin density wave (PSDW) side, there are two quantum phase transitions from the commensurate PSDW to an in-commensurate PSDW and then to the excitonic superfluid state. We compare our theory with experimental data and also the previous microscopic calculations.Comment: 4+ pages, 2 figures. 1 table, Final version to appear in Phys. Rev. Let

Acoustic Attenuation by Two-dimensional Arrays of Rigid Cylinders

In this Letter, we present a theoretical analysis of the acoustic transmission through two-dimensional arrays of straight rigid cylinders placed parallelly in the air. Both periodic and completely random arrangements of the cylinders are considered. The results for the sound attenuation through the periodic arrays are shown to be in a remarkable agreement with the reported experimental data. As the arrangement of the cylinders is randomized, the transmission is significantly reduced for a wider range of frequencies. For the periodic arrays, the acoustic band structures are computed by the plane-wave expansion method and are also shown to agree with previous results.Comment: 4 pages, 3 figure

Nuclear transparency in quasielastic A(e,e'p): intranuclear cascade versus eikonal approximation

The problem of nuclear propagation through the nuclear medium in quasielastic A(e,e'p) reactions is discussed in the kinematic range 1<Q^2<7 (GeV/c)^2. The coefficient of nuclear transparency is calculated for each Q^2 in the framework of the intranuclear cascade model (INC) and of the eikonal approximation (EA). The predictions of both models are in good agreement with each other and with experimental data recently obtained at SLAC, BATES and TJNAF. The EA gives an explanation of the Q^2 behaviour of the transparency coefficient as a kinematic effect related to the superposition of contributions from each target shell.Comment: RevTeX, 23 pages, 11 figures separately, submitted to Phys. Rev.