Thermal conductance of nanostructured phononic crystals - art. no. 172301

The thermal conductance of mechanically suspended nanostructures has recent ly received much attention, in part due to the recent prediction and observ ation of the quantum limit for thermal conductance, which is observed in lo ng, thin insulating beams at very low temperatures [D. E. Angelescu, M. C. Cross, and M. L. Roukes, Superlattices Microstruct. 23, 673 (1998); K. Schw ab, E. A. Henriksen, J. M. Norlock, and M. L. Roukes, Nature 404, 974 (2000 ); I. G. C. Rego and G. Kirczenow, Phys. Rev. Lett. 81. 232 (1998); M. P, B lencowe. Phys. Rev. B 59. 4992 (1999)]. In this brief report, we describe a model calculation where the simple beam used to calculate quantum conducta nce [L. G. C. Rego and G. Kirczenow, Phys. Rev. Lett. 81, 232 (1998)] is re placed by a beam made from an artificial one-dimensional phononic crystal. We find that at the lowest temperatures and longest thermal-phonon waveleng ths, the quantum limit is recovered, while for intermediate temperatures, w here the dominant phonon wavelength is of the order of the phononic-crystal repeat distance, a significant suppression of the conductance is predicted . At higher temperatures the conductance returns to that of a simple beam.