Revealing the ultra-sensitive calorimetric properties of supercon-ducting magic-angle twisted bilayer graphene

TL;DR

This study uncovers the ultra-sensitive calorimetric properties of superconducting magic-angle twisted bilayer graphene (MATBG), demonstrating its potential for revolutionary photon detection with extremely low noise and fast operation speeds.

Contribution

It provides the first experimental measurement of thermal conductance and photo-response in superconducting MATBG, highlighting its suitability for ultra-sensitive calorimetric applications.

Findings

Thermal conductance Gth = 0.19 pW/K at 35mK

Peak responsivity S = 5.8 x 10^7 V/W near critical current

Theoretical NEP limit < 10^-20 WHz^-1/2

Abstract

The allegedly unconventional superconducting phase of magic-angle twisted bilayer graphene (MATBG)1 has been predicted to possess extraordinary thermal properties, as it is formed from a highly diluted electron ensemble with both a record-low carrier density n ~ 10^11 cm-2 and electronic heat capacity Ce < 100 kB. While these attributes position MATBG as a ground-breaking material platform for revolutionary calorimetric applications2, these properties have so far not been experimentally shown. Here we reveal the ultra-sensitive calorimetric properties of a superconducting MATBG device, by monitoring its temperature dependent critical current Ic under continuous laser heating with a wavelength of 1550nm. From the bolometric effect, we are able to extract the temperature dependence of the electronic thermal conductance Gth, which remarkably has a non-zero value Gth = 0.19 pW/K at 35mK and in the low temperature limit is consistent with a power law dependence, as expected for nodal superconductors. Photo-voltage measurements on this non-optimized device reveal a peak responsivity of S = 5.8 x 10^7 V/W when the device is biased close to Ic, with a noise-equivalent power of NEP = 5.5 x 10^-16 WHz^-1/2. Analysis of the intrinsic perfor-mance shows that a theoretically achievable limit is defined by thermal fluctuations and can be as low as NEPTEF < 10^-20 WHz-1/2, with operation speeds as fast as ~ 500 ns. This establishes superconducting MATBG as a revolutionizing active material for ultra-sensitive photon-detection applications, which could enable currently unavailable technologies such as THz photon-number-resolving single-photon-detectors.