ICT2014 Abstracts

Heat, a measure of entropy, is largely perceived to be diffusive and transported incoherently by charge carriers (electrons and holes) and lattice vibrations (phonons) in a material. Because heat can be carried by many different (quasi-)particles, it is generally hard for us to spatially localize the transport of thermal energy. Therefore, heat transport is considered a challenging means of the local imaging of a material and of its electronic states. Recently we have shown [1,2] that coherent electron and heat transport through a point-like contact in the atomic force microscope set-up at the ultra-high vacuum condition produces an atomic Seebeck effect, which represents the novel imaging principle of surface wave functions with atomic resolution. The heat-based scanning Seebeck microscopy clearly contrasts to the vacuum tunneling-based scanning tunneling microscopy, a hitherto golden standard of imaging surface wave functions. We have found that the coherent transmission probabilities of electron and phonon across the tip-sample junction are equally important for the imaging capability of the scanning Seebeck microscope. Electron transport contributes through the mesoscopic Seebeck coefficient, which is approximately proportional to the logarithmic energy derivative of local density of states at the Fermi energy. Phonon transport contributes to the atomic Seebeck effect through the interfacial temperature drop at the tip-sample junction, which, we found, correlates with van der Waals interaction dependent on atom-to-atom interaction at the interface. We will also discuss how we can simulate the atomic Seebeck effect from first-principles surface wave functions, and compare the results with experimental thermoelectric images in order to identify the atomic structure of defects in graphene.

[1] S. Cho, S. D. Kang, W. Kim, E.-S. Lee, S.-J. Woo, K.-J. Kong, I. Kim, H.-D. Kim, T. Zhang, J. A. Stroscio, Y.-H. Kim and H.-K. Lyeo, arXiv:1305.2845, Nature Mater. 12, 913 (2013).

[2] E.-S. Lee, S. Cho, H.-K. Lyeo and Y.-H. Kim, arXiv:1307.3742, Phys. Rev. Lett., in production (2014).