Development of Superconducting Tunnel Junction Detector Using Hafnium for COBAND Experiment
We present the development of a Superconducting Tunnel Junction detector using hafnium (Hf-STJ) as a far infrared single photon detector for COsmic BAckground Neutrino Decay search (COBAND) experiment. The photon energy spectrum from the decay of cosmic background neutrino is expected to have a sharp edge at the high energy end in a far-infrared region ranging from 14–25 meV in the cosmic infrared background and the overwhelming infrared foreground from the zodiacal emission. We are developing a Hf-STJ which is expected to have 2% energy resolution for a single photon of 25 meV. We have successfully produced a superconductor-insulator-superconductor structure using Hf. However, it is found to suffer from a large leakage current and needs modification of the Hf-STJ to reduce it. We have developed two new types of Hf-STJ: Hf-STJ with an Al layer and Hf-STJ with a new sputtering condition. The leakage current density of two new types of Hf-STJ becomes 16 times smaller than the old Hf-STJ and obtained a response to the visible light. Because of its large leakage current, further optimization is underway.
KeywordsNeutrino decay Superconducting tunnel junction Hafnium
This work was supported by the Ministry of Education, Science, Sports and Culture of Japan (MEXT KAKENHI Grant Number 25105007). We also thank KEK Detector Technology Project for supporting us in development of STJs at KEK.
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