부산대학교 도서관

Localization of elastic waves in two-dimensional (2D) and three-dimensional (3D) media with random distributions of the Lam\'e coefficients (the shear and bulk moduli) is studied, using extensive numerical simulations. We compute the frequency-dependence of the minimum positive Lyapunov exponent $\gamma$ (the inverse of the localization length) using the transfer-matrix method, the density of states utilizing the force-oscillator method, and the energy-level statistics of the media. The results indicate that all the states may be localized in the 2D media, up to the disorder width and the smallest frequencies considered, although the numerical results also hint at the possibility that there might a small range of the allowed frequencies over which a mobility edge might exist. In the 3D media, however, most of the states are extended, with only a small part of the spectrum in the upper band tail that contains localized states, even if the Lam\'e coefficients are randomly distributed. Thus, the 3D heterogeneous media still possess a mobility edge. If both Lam\'e coefficients vary spatially in the 3D medium, the localization length $\Lambda$ follows a power law near the mobility edge, $\Lambda\sim(\Omega-\Omega_c)^{-\nu}$, where $\Omega_c$ is the critical frequency. The numerical simulation yields, $\nu \simeq 1.89\pm 0.17$, significantly larger than the numerical estimate, $\nu\simeq 1.57\pm 0.01$, and $\nu=3/2$, which was recently derived by a semiclassical theory for the 3D Anderson model of electron localization...
Comment: 10 pages, 9 figures