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

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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.