Dirac cones at (k)over-right-arrow=0 in acoustic crystals and zero refractive index acoustic materials

We show that two-dimensional acoustic crystals (ACs) can be designed to exhibit Dirac cone dispersion at (k) over right arrow = 0. Effective medium theory finds that some of these ACs can have effectively zero reciprocal of bulk modulus 1/kappa(eff) and zero mass density rho(eff), and thus zero refractive indices at the Dirac point. Numerical simulations are used to demonstrate various phenomena associated with the zero spatial phase change inside such materials. (C) 2012 American Institute of Physics. [doi:10.1063/1.3686907]