Tin- and lead-tunnel junctions as quantitative detector for intense thermal phonon pulses |
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Authors: | M Nover O Weis |
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Institution: | (1) Abteilung für Festkörperphysik der Universität Ulm, Oberer Eselsberg, D-7900 Ulm/Donau, Federal Republic of Germany;(2) Present address: Krupp Forschungsinstitut, 4300 Essen, FRG |
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Abstract: | Pulse-heated constantan films emit thermal phonon pulses into an a-cut sapphire held at a temperature of some Kelvin. The frequencies of these thermal phonons depend on the radiation temperature and can easily be shifted into the THz range. After a path of 6 mm these phonons are detected by observing the momentary current/voltage characteristics of evaporated symmetric tin- or lead-tunnel junctions during irradiation time. These characteristics correspond to characteristics taken in thermal equilibrium at higher substrate temperature which means that a momentary temperature of the electronic system can be deduced. Using a set of model assumptions concerning phonon transmission across interfaces, phonon propagation in the anisotropic sapphire, absorption in the superconducting detector film and reemission of the absorbed power into the substrate, a comparison with theoretically expected diode temperatures within the one-temperature model for the detector material can be made. Using a variety of quite different experimental conditions there is a remarkable and astonishing well agreement between experiment and theory by fitting only two parameters for each phonon polarization and metal:i) the phonon absorption coefficient in the normal state andii) a phonon cutoff-frequency for the detected phonons. From this fit an information about these important, so far unknown parameters is achieved.Supported by Deutsche Forschungsgemeinschaft |
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