Thermal conductance through discrete quantum channels

We have observed a quantized limiting value of the thermal conductance for each propagating phonon channel in a one-dimensional (1D), ballistic phonon waveguide: g(0) = pi (2)k(B)(2)T/3h. To achieve this we have developed nan ostructures with full three-dimensional relief that incorporate integral th ermometers and heaters. These devices are comprised of an isolated thermal reservoir (phonon cavity) suspended above the sample substrate by four narr ow insulating beams (phonon waveguides) with lateral dimensions similar to 100 nm. We employ DC SQUID noise thermometry to measure the temperature of the phonon cavity non-perturbatively. Direct electrical contact from the su spended nanostructure to the room-temperature environment, crucial for thes e experiments, is attained by means of a very significant level of electric al filtering. These first experiments provide access to the mesoscopic regi me for phonons, and open intriguing future possibilities for exploring ther mal transport in very small systems. We are currently adapting and improvin g the ultrasensitive, extremely low dissipation DC SQUID techniques utilize d in this work toward the ultimate goal of detecting individual thermal pho nons. (C) 2001 Elsevier Science B.V. All rights reserved.