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High sensitivity and fast response are the most important metrics for infrared sensing and imaging and together form the primary tradeoff space in bolometry. To simultaneously improve both characteristics requires a paradigm shift on the thermal properties of bolometric materials. Due to a vanishingly small density of states at the charge neutrality point, graphene has a record-low electronic heat capacity which can reach values approaching one Boltzmann constant Ce ~ kb. In addition, its small Fermi surface and the high energy of its phonons result in an extremely weak electron-phonon heat exchange. The combination will allow a strong thermal isolation of the electrons in graphene for higher sensitivity without sacrificing the detector response time. These unique thermal properties and its broadband photon absorption, make graphene a promising platform for ultrasensitive and ultra-fast hot electron bolometers, calorimeters and single photon detectors for low energy light.
Here, we introduce a hot-electron bolometer based on a novel Johnson noise readout of the electron gas in graphene [1,2,3], which is critically coupled to incident radiation through a photonic nanocavity. This proof-of-concept operates in the telecom spectrum, achieves an enhanced bolometric response at charge neutrality with a noise equivalent power NEP < 5pW/√Hz, a thermal relaxation time of τ < 34ps, an improved light absorption by a factor ~3, and an operation temperature up to T=300K [3]. Altogether this shows that our proof-of-concept device can be a promising bolometer with efficient light absorption and a superior sensitivity-bandwidth product. Since the detector also has no limitations on its operation temperature, it provides engineering flexibility, which overall opens a new route for practical applications in the fields of thermal imaging, observational astronomy, quantum information and quantum sensing. In particular, since it is more than 5 times faster than the bandwidth of the intermediate frequency in the hot electron bolometer mixer, it can be employed as a cutting edge bolometric mixer material.
[1] K. C. Fong, PRX, 2 (2012);
[2] J. Crossno et.al., Science, 351 (2016);
[3] D. K. Efetov et. al., Nature Nano. (2018));
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