# 18th International Workshop on Low Temperature Detectors (LTD-18)

22-26 July 2019
Milano
Europe/Rome timezone

## The end of unexplained noise? A New Model for Noise in TESs

26 Jul 2019, 11:15
15m
Auditorium G. Testori (Milano)

### Auditorium G. Testori

#### Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
Oral Presentation Low Temperature Detector Development and Physics

### Speaker

Dr Douglas Bennett (NIST)

### Description

As demanding applications such as x-ray spectroscopy push transition-edge sensors (TESs) to even better energy resolution, it is critical to understand all their potential noise sources. Since the early days of TESs, many groups have observed a broadband voltage noise that could not be explained by known noise mechanisms. In 2004, Ullom et al.[1] showed this unexplained noise could be suppressed using both device geometry and an applied magnetic field. However, despite more than a decade of effort, the magnitude of the unexplained noise in TESs is still not understood. Some progress was made in 2006 [2], when Irwin predicted an enhancement of the Johnson noise based on an analysis of non-linear bolometers near equilibrium. This analysis predicted that the noise level in a TES is equal to the Johnson noise due to the TES resistance at its operating point multiplied by a factor of $(1+2\beta_I)$. In some scenarios the (1+2$\beta_I$) term has reasonably predicted the amount of Johnson noise. In many other scenarios, especially low in the transition, and for devices with high $\alpha_I$ and high $\beta_I$, the $(1+2\beta_I)$ expression dramatically underpredicts the observed noise [3].

To resolve this mystery, we present a new noise model for TESs that takes into account their junction nature and the shape of the $R(I,T)$ surface. We present analytical expressions for the unexplained noise within the context of the RSJ and two-fluid models. We also present an expression for the unexplained noise for an arbitrary $R(I,T)$ surface. We then compare these expressions with the measured noise in different TESs and at different operating resistances. Initial testing shows good agreement between measurement and theory.

[1] Ullom, Joel N., et al., Appl. Phys. Lett., 84 (2004) 4206.
[2] Irwin, Kent D., Nucl. Instrum. Methods Phys. Res. A, 559 (2006) 718.
[3] Jethava, Nikhil, et al., AIP Conference Proceedings., 1185 (2009) 31.

Less than 5 years of experience since completion of Ph.D N N

### Primary authors

Dr Douglas Bennett (NIST) Abigail Wessels (National Institute of Standards and Technology) Kelsey Morgan (National Institute of Standards and Technology) Dr Johnathon Gard (NIST) Gene Hilton (NIST-Boulder) Christine Pappas (National Institute of Standards and Technology) Carl Reintsema (National Institute of Standards and Technology) Daniel Schmidt (NIST) Daniel Swetz (National Institute of Standards and Technology) Joel Weber (NIST) Joel Ullom (NIST/University of Colorado)