Artificial quantum states on semiconductor surfaces created and probed by cryogenic scanning tunneling microscopy

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Cryogenic scanning tunneling microscopy (STM) is used to create artificial quantum structures on semiconductor surfaces and explore their electronic properties by scanning tunneling spectroscopy (STS). To create the structures, we developed a highly controllable way of atom manipulation on the InAs(111)A surface. Pristine InAs(111)A hosts a surface state and a low coverage of native In adatoms. The adatoms are positively charged and can be repositioned by the STM tip, making it possible to engineer the electrostatic potential landscape and induce carrier confinement on the atomic length scale and with atomic precision. We demonstrated that single quantum dots and quantum-dot molecules with a perfectly defined energy level structure can be created in this way. We also constructed dimerized quantum-dot chains revealing electronic states localized at the ends and at internal domain walls, consistent with topological boundary states predicted by the Su-Schrieffer-Heeger (SSH) model. Building on our previous work, we plan to address three major objectives (topical areas) in the new project period: (i) In-depth analysis and full description of the energy level structure of quantum-dot molecules accounting for hybridization effects that go beyond a simple s-orbital tight-binding model. (ii) Extension to artificial quantum-dot assemblies on the (110)-cleaved InAs surface, the latter offering significantly larger terrace sizes and hence the construction of more extended structures such as Kagomé lattices and two-dimensional analogues of the SSH model. (iii) STM/STS and atom manipulation on (110)-cleaved III-V semiconductor heterostructures with a band-edge design involving wide band gap layers embedded in narrow band gap layers; we anticipate that the results of this topical area will lie the groundwork for future research aiming at the implementation of external electrodes to enable electrical gating of the STM-generated quantum structures. Perfectly defined and tunable surface structures on semiconductors as investigated in our project provide detailed insight into the behavior of electrons in reduced dimensions. This insight is important both for fundamental science and future quantum technologies.