Application of Bragg superlattice filters in low temperature microrefrigerators

Abstract

We propose to use the Bragg interference filter technology for fabrication of microrefrigerators. The idea of using superconductor-insulator-superconductor (SIS) or normal metal-insulator-superconductor (SIN) tunnel junctions as cooling elements in micro-refrigerators is attractive because of the absence of (micro-) refrigerators operating below 150 K. The microscopic approach to cooling is based on the "phonon deficit effect" in nonequilibrium regime of tunnel junctions. This effect can be improved by use of phonon filters placed between the tunnel junction and the heath-bath. Such a filter can be the Bragg interference superlattice (Bragg's grating) which is well studied for problems of optical communications. Bragg interference filters are used also for detection of phonons emitted by tunnel junctions. To enhance the refrigeration process one needs filters with very broad spectral transmission properties or a large transmission band with one or two narrow stop bands. The type of the needed filter will depend on the types of the used tunnel junction. Corresponding discussion is presented.