Bragg diffraction of microcavity polaritons by a surface acoustic wave

Bragg scattering of polaritons by a coherent acoustic wave is mediated and strongly enhanced by the exciton states resonant with the acoustic and optic fields in the intraband and interband transitions, respectively. In this case, in contrast with conventional acousto-optics, the resonantly enhanced Bragg spectra reveal the multiple orders of diffracted light. For polaritons in GaAs microcavities driven by a surface acoustic wave of νSAW=1 GHz and Iac≲100 W/cm2 the main acoustically induced band gap can be as large as ΔMCac≃0.6 meV and the Bragg replicas up to n=3 can be observed

Magic Numbers and Optical Absorption Spectrum in Vertically Coupled Quantum Dots in the Fractional Quantum Hall Regime

Exact diagonalization is used to study the quantum states of vertically coupled quantum dots in strong magnetic fields. We find a new sequence of angular momentum magic numbers which are a consequence of the electron correlation in the double dot. The new sequence occurs at low angular momenta and changes into the single dot sequence at a critical angular momentum determined by the strength of the inter-dot electron tunneling. We also propose that the magic numbers can be investigated experimentally in vertically coupled dots. Because of the generalized Kohn theorem, the far-infrared optical absorption spectrum of a single dot is unaffected by correlation but the theorem does not hold for two vertically coupled dots which have different confining potentials. We show that the absorption energy of the double dot should exhibit discontinuities at the magnetic fields where the total angular momentum changes from one magic number to another.Comment: 4 pages, 3 Postscript figures, RevTeX. (to appear in Phys.Rev.B

Evaluation of Mode I Fracture Toughness Assisted by the Numerical Determination of K-Resistance

The fracture toughness of a rock often varies depending on the specimen shape and the loading type used to measure it. To investigate the mode I fracture toughness using semi-circular bend (SCB) specimens, we experimentally studied the fracture toughness using SCB and chevron bend (CB) specimens, the latter being one of the specimens used extensively as an International Society for Rock Mechanics (ISRM) suggested method, for comparison. The mode I fracture toughness measured using SCB specimens is lower than both the level I and level II fracture toughness values measured using CB specimens. A numerical study based on discontinuum mechanics was conducted using a two-dimensional distinct element method (DEM) for evaluating crack propagation in the SCB specimen during loading. The numerical results indicate subcritical crack growth as well as sudden crack propagation when the load reaches the maximum. A K-resistance curve is drawn using the crack extension and the load at the point of evaluation. The fracture toughness evaluated by the K-resistance curve is in agreement with the level II fracture toughness measured using CB specimens. Therefore, the SCB specimen yields an improved value for fracture toughness when the increase of K-resistance with stable crack propagation is considered

Reconstruction of macroscopic Maxwell equations: a single susceptibility theory

This book discusses the electromagnetic response function of matter, providing a logically more complete form of macroscopic Maxwell equations than the conventional literature. It shows that various problems inherent to the conventional macroscopic Maxwell equations are solved by the first-principles derivation presented. Applying long wavelength approximation to microscopic nonlocal response theory results in only one susceptibility tensor covering all the electric, magnetic and chiral polarizations, and the book provides its quantum mechanical expression in terms of the transition energies of matter and the lower moments of corresponding current density matrix elements. The conventional theory in terms of epsilon and mu is recovered in the absence of chirality under the condition that magnetic susceptibility is defined with respect to not H, but to B. This new edition includes discussions supporting the basis of the present electromagnetic response theory in a weakly relativistic regime, showing the gauge invariance of many-body Schroedinger equation with explicit Coulomb potential, the relationship between this theory and the emergent electromagnetism, and the choice of appropriate forms of single susceptibility theory and chiral constitutive equations