Scanning Tunneling Microscopy Study of Electronic Behavior in Semiconducting Nanowires
November 8, 2018 @ 3:00 pm
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Electrons confined to one dimension exhibit various counter-intuitive phenomena such as charge fractionalization, spin-charge separation, and Majorana end modes induced at nanowires rendered topologically superconducting. In my research I have performed spectroscopic mappings of the electronic states in InAs nanowires through scanning tunneling microscopy and probed their one-dimensional electronic structure. This research was made possible by developing a method to maintain the molecular beam epitaxially grown nanowires under ultra-high vacuum. This procedure uniquely allows us to atomically resolve the pristine facets of the nanowires, to detect the electronic quantized spectrum through Van-Hove singularities and to visualize the quantized subbands through the interference patterns the one-dimensional electronic states embed in the local density of states as they scatter off defects. In bare nanowires we identified a novel effect driven by the strong electron-electron interactions in one-dimension. At high energies, relaxation dynamics is manifestly different from the relaxation of low energy excitation, and hot electrons regain their phase coherence. The origin of this unusual energy-evolution of phase coherence lies in the form of the effective Coulomb interaction in one-dimension that increasingly decouples the hot electrons from the cold Fermi sea. We have further measured nanowires with epitaxial aluminium layer, and studied the effect of the Coulomb interaction in small islands configuration. The importance of this material system in the framework of current realizations of Majorana modes renders the input we can provide on the Al/InAs interface valuable to future experiments.