Vol.:(0123456789) Journal of Low Temperature Physics https://doi.org/10.1007/s10909-020-02395-5 1 3 The Role of Multiple Fluctuation Events in NbN and NbTiN Superconducting Nanostrip Single‑Photon Detectors L. Parlato 1,2  · D. Salvoni 1,2  · M. Ejrnaes 2  · D. Massarotti 3  · R. Caruso 1,4  · R. Satariano 4  · F. Tafuri 1,2  · X. Y. Yang 5  · L. You 5,6  · Z. Wang 5,6  · G. P. Pepe 1,2  · R. Cristiano 2 Received: 16 July 2019 / Accepted: 5 February 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract We report on measurements of the switching current distributions on two-dimen- sional NbN superconducting nanostrip single-photon detectors (SNSPD), 5 nm thick and 80 nm wide, in an interval of temperatures from 6 K down to 0.3 K and compare the data with those obtained for similar NbTiN nanostrips. The standard deviations of the switching distributions show an extended region at high temperatures where multiple phase slip switching events occur. This is probably related to a decreas- ing critical current and an increasing electron and phonon heat capacities. In this temperature region, the width of the switching distribution, and therefore the dark count rate, is considerably reduced down to values below those observed at the low- est temperature. Finally, we also quantify the energy scale of the fuctuation phe- nomena. The proposed experimental approach may result in a powerful tool for the diagnostic of SNSPD operation mode. Keywords Superconducting nanostrip single-photon detectors · Dark count rate · Fluctuation events * L. Parlato lparlato@unina.it 1 Dipartimento di Fisica, Università degli Studi di Napoli Federico II, 80125 Naples, Italy 2 Consiglio Nazionale delle Ricerche – Institute of Superconductors, Innovative Materials and Devices, Naples, Italy 3 Dipartimento di Ingegneria Elettrica e delle Tecnologie dell’Informazione, Università degli Studi di Napoli Federico II, 80125 Naples, Italy 4 SeeQC-eu, Via dei Due Macelli 66, 00187 Rome, Italy 5 State Key Lab of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), 865 Changning Rd., Shanghai 200050, People’s Republic of China 6 CAS Center for Excellence in Superconducting Electronics (CENSE), 865 Changning Rd., Shanghai 200050, People’s Republic of China