Enhancement of ballistic thermal conductance in three dimensional double stub structures

We investigate ballistic thermal conductance in three dimensional double stub structures by using the scattering-matrix method. It is found that in such structures the thermal conductance can be clearly enhanced by inhomogeneities despite of the phonon scattering. When the stress-free boundary condition is employed, the enhancement can be observed only at very low temperature, and such the enhancement is strongly sensitive to the coupling length between two stubs. However, when the hall-wall boundary condition is employed, the enhancement can be observed in all explored temperature range, and becomes insensitive to the coupling length. A brief analysis of these results is given.