Mahmoud Lababidi, Erhai Zhao
Massless Dirac electrons on the surface of a three-dimensional topological insulator (TI) can be turned into exotic excitations by proximity coupling to superconductors. For example, Majorana fermions with a linear dispersion, $E\sim k$, exist in a short $\pi$ Josephson junction on the TI surface. We show that in these systems, the Andreev bound states spectrum turns into a nearly flat band at zero energy when the chemical potential is sufficiently away from the Dirac point. The flat dispersion is well approximated by $E\sim k^N$, where $N$ scales with the chemical potential. Similar evolution from linear to flat dispersion also occurs for the subgap spectrum of a periodic superconducting proximity structure, such as a TI surface in contact with a stripe superconductor.
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http://arxiv.org/abs/1207.5534
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