Nanoscale thermal imaging of dissipation from individual atomic defects in graphene

Energy dissipation is a fundamental process governing the dynamics of classical and quantum systems. Despite its vital importance, direct imaging and microscopy of dissipation in quantum systems is currently impossible because the existing thermal imaging methods lack the necessary sensitivity and are unsuitable for low temperature operation. 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 nanothermometer providing cryogenic thermal imaging with four orders of magnitude improved thermal sensitivity of below 1 µK/Hz^1/2 [2]. The non-contact non-invasive thermometry allows thermal imaging of minute energy dissipation down to the fundamental Landauer limit of 40 fW for continuous readout of a single qubit at 1 GHz at 4.2 K. By varying potential between the SQUID-on-tip and the sample a nanoscale spectroscopic analysis of the dissipation process can be attained. 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] D. Halbertal, J. Cuppens, M. Ben Shalom, L. Embon, N. Shadmi, Y. Anahory, H. R. Naren, J. Sarkar, A. Uri, Y. Ronen, Y. Myasoedov, L. S. Levitov, E. Joselevich, A. K. Geim, and E. Zeldov, Nature 539, 407 (2016).
[3] D. Halbertal, M. Ben Shalom, A. Uri, K. Bagani, A.Y. Meltzer, I. Marcus, Y. Myasoedov, J. Birkbeck, L.S. Levitov, A.K. Geim, and E. Zeldov, arXiv:1710.01486 (Science in press).