Tunable STM tip gating effect in graphene: from quantum confinement to optical guiding
8 maart 2017
UAntwerpen, Campus Groenenborger, T.138 - Groeneborgerlaan 171 - 2020 Antwerpen
16 - 17 uur
Organisatie / co-organisatie:
Condensed Matter Theory
Condensed Matter Theory seminar presented by Dr Dean Moldovan
Apart from just measuring sample properties, the tip of scanning tunneling microscope (STM) may also be used as a secondary gate which offers an additional knob for experiments. The profile of the tip-induced electric potential depends on the geometry of the tip (sharp vs. blunt), the tip-sample work function difference (which may be changed by coating the tip with various materials) and the applied bias and back-gate voltages (which allow for continuous tuning).
The gating effect produces a circular pn-junction that can be tuned from the nanometer-scale, where quantum effects are dominant, to the micrometer scale where optical-guiding takes over (massless Dirac-electrons in graphene mimic the propagation of photons). We find that in the nanometer-scale junction electrons are trapped in states that resemble atomic collapse at a supercritical charge. As the junction size increases, the transition to optical-guiding is signaled by the emergence of whispering-gallery modes.
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