Models of two level systems for anisotropic glassy materials

We use an extended version of the standard tunneling model to explain the sound absorption in anisotropic glassy materials and heat transport in mesoscopic slabs and bridges. The glassy properties are determined by an ensemble of two level systems (TLS). In our model a TLS is characterized by a $3\times3$ symmetric tensor, $[T]$, which couples to the strain field, $[S]$, through a $3\times3\times3\times3$ tensor of coupling constants, $[[R]]$. The structure of $[[R]]$ reflects the symmetry of the host lattice. We also propose microscopic theoretical methods and models of TLS by which we test some of the most well known models of glassy materials, together with our own model.