One component surface waves in materials with symmetry

The existence of one-component surface waves in materials with a plane of symmetry normal to the direction of propagation is discussed, with particular attention given to transversely isotropic materials in this class. A unique feature of these waves is that the traction vector which vanishes at the free surface is zero at all depths, implying that one-component surface waves are also pure modes of slabs. All of the `theoretical materials´ which support the wave have the unusual property that at least one Poisson´s ratio must be negative