Calorimetric observation of single He2* excimers in a 100 mK He bath

TL;DR

This paper demonstrates the first calorimetric detection of individual He2* excimers in superfluid helium at 100 mK using a superconducting TES, enabling detection of both singlet and triplet states through photon absorption and surface interaction.

Contribution

It introduces a novel calorimetric method for detecting single He2* excimers in superfluid helium with high energy resolution, capturing both singlet and triplet states.

Findings

Successful detection of He2* excimers via calorimetry.

Differentiation between singlet and triplet states based on detection signals.

First calorimetric observation of individual He2* excimers in superfluid helium.

Abstract

We report the first calorimetric detection of individual He2* excimers within a bath of superfluid 4He. The detector used in this work is a single superconducting titanium transition edge sensor (TES) with an energy resolution of ~1 eV, immersed directly in the helium bath. He2* excimers are produced in the surrounding bath using an external gamma-ray source. These excimers exist either as short-lived singlet or long-lived triplet states. We demonstrate detection of both states: in the singlet case the calorimeter records the absorption of a prompt 15 eV photon, and in the triplet case the calorimeter records a direct interaction of the molecule with the TES surface, which deposits a distinct fraction of the 15 eV, released upon decay, into the surface. We also briefly discuss the detector fabrication and characterization.