Jul 22 – 26, 2019
Europe/Rome timezone

R&D of Hf-STJ for COBAND experiment

Jul 25, 2019, 5:45 PM
1h 15m
Piazza Città di Lombardia (Milano)

Piazza Città di Lombardia


Piazza Città di Lombardia, 1, 20124 Milano MI
Poster Low Temperature Detector Development and Physics Poster session


Ms Chisa Asano (University of Tsukuba)


Discovery of neutrino oscillations revealed that neutrinos have mass, but the absolute mass of the neutrinos still remains unknown. Since neutrinos are a massive particle, a heavier neutrino may decay into a lighter one with a photon emission. The photon energy is expected to be around 25 meV at maximum. The COsmic BAckground Neutrino Decay (COBAND) experiment aims at detecting the photons as decay products of cosmic neutrino background (C\nuB) and determining the neutrino mass. In addition, if we observe excess photons in the C\nuB decay from the prediction by the standard model (SM), it will indicate a physics beyond the SM. Therefore, the detector required in the COBAND experiment is to be capable to measure single photons with a resolution better than 2% at the energy of 25 meV to identify the photons from the two-body decay of neutrinos. Since semiconductor-based detectors cannot satisfy this requirement, we consider using superconducting tunnel junction devices based on hafnium (Hf-STJ), which is known to have the smallest superconducting gap at typical temperatures of low-temperature detector instrumentation. We have established dependable fabrication method to form a SIS structure of Hf-STJ. We also observed pulsed visible photons using the Hf-STJ devices. The leakage current, however, was still found to be much larger than 10 pA of the COBAND requirement. Here we report on the latest measurement and the recent progress of Hf-STJ development for small junction devices. We will discuss the junction-size dependence of the leakage current together with fabrication details on the sputtering conditions of Hf and oxidization method to form an insulation layer. Moreover, we will present the 6 keV x-ray responses measured in an adiabatic demagnetization refrigerator.

Student (Ph.D., M.Sc. or B.Sc.) Y
Less than 5 years of experience since completion of Ph.D N

Primary author

Ms Chisa Asano (University of Tsukuba)


Prof. Shinhong Kim (University of Tsukuba) Prof. Yuji Takeuchi (University of Tsukuba) Dr Takashi Iida (University of Tsukuba) Mr Akihiro Kasajima (University of Tsukuba) Dr Kenichi Takemasa (University of Tsukuba) Prof. Yong-Hamb Kim (Institute for Basic Science) Ms Hyejin Lee (Institute for Basic Science) Prof. Hirokazu Ikeda (Institute of Space and Astronautical Science) Dr Takehiko Wada (Institute of Space and Astronautical Science) Dr Kouichi Nagase (Institute of Space and Astronautical Science) Prof. Shuji Matsuura (Kwansei gakuin University) Dr Yasuo Arai (High Energy Accelerator Research Organization) Dr Ikuo Karachi (High Energy Accelerator Research Organization) Prof. Masashi Hazumi (High Energy Accelerator Research Organization) Prof. Takuo Yoshida (University of Fukui) Dr Satoshi Mima (RIKEN) Dr Kenji Kiuchi (University of Tokyo) Prof. Hirokazu Ishino (Okayama University) Prof. Atsuko Kibayashi (Okayama University) Dr Yukihiro Kato (Kindai University) Dr Go Fujii (Advanced Industrial Science and Technology (AIST)) Dr Shigetomo Shiki (Advanced Industrial Science and Technology (AIST)) Dr Masahiro Ukibe (Advanced Industrial Science and Technology (AIST)) Dr Masataka Ohkubo (Advanced Industrial Science and Technology (AIST)) Prof. Shoji Kawahito (Shizuoka University) Prof. Eric Ramberg (Fermi National Accelerator Laboratory) Prof. Paul Rubinov (Fermi National Accelerator Laboratory) Prof. Dmitri Sergatskov (Fermi National Accelerator Laboratory) Prof. Soo-Bong Kim (Seoul National University)

Presentation materials