Voltage Fluctuations in ac Biased Superconducting Transition-Edge Sensors

• Published in: Physical review letters Vol. 126; no. 21; p. 217001
• Main Authors: Gottardi, L, de Wit, M, Taralli, E, Nagayashi, K, Kozorezov, A
• Format: Journal Article
• Language: English
• Published: College Park American Physical Society 26-05-2021
• Subjects: Alternating current; Electrical measurement; Elementary excitations; Higher harmonics; Noise; Nonlinear response; Sensors; Superconductivity; Thermal noise
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.126.217001

We present a detailed analysis of the fundamental noise sources in superconducting transition-edge sensors (TESs), ac voltage biased at MHz frequencies and treated as superconducting weak links. We have studied the noise in the resistive transition as a function of bath temperature of several detectors with different normal resistances and geometries. We show that the "excess" noise, typically observed in the TES electrical bandwidth, can be explained by the equilibrium Johnson noise of the quasiparticles generated within the weak link. The fluctuations at the Josephson frequency and higher harmonics contribute significantly to the measured voltage noise at the detector bandwidth through the nonlinear response of the weak link with a sinusoidal current-phase relation.