Nano-imaging of heat dissipation from individual atomic defects in graphene

Energy dissipation is a fundamental process governing the dynamics of classical and quantum systems, even though direct imaging of dissipation in quantum systems remained out-of-reach experimentally until recently. We developed a scanning nanoSQUID with sub 50 nm diameter that resides at the apex of a sharp pipette [1] acting simultaneously as nanomagnetometer with single spin sensitivity and as nano-thermometer providing cryogenic thermal imaging with four orders of magnitude improved thermal sensitivity of below 1 µK/Hz^1/2 [2]. Using this scanning nano-thermometry we visualize and control phonon emission due to inelastic electron scattering off individual atomic defects in graphene [3]. The inferred electron-phonon “cooling power spectrum” exhibits sharp peaks when the Fermi level comes into resonance with electronic quasi-bound states at such defects, a hitherto uncharted process. The atomic defects are very rare in the bulk but abundant at the edges, acting as switchable atomic-scale phonon emitters that establish the dominant dissipation mechanism in graphene.

[1] Vasyukov et al., Nature Nanotech. 8, 639 (2013).
[2] Halbertal et al., Nature 539, 407 (2016).
[3] Halbertal et al., Science 358, 1303-1306 (2017).