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Artificial quantum states on semiconductor surfaces generated and investigated using low-temperature scanning tunneling microscopy

01/02/2024 - 31/01/2027

Left panel: STM topography image (0.1 nA, 0.1 V) of two In6 dots at a center-to-center spacing of 72.85 Å; each dot consists of six In adatoms on InAs(110) assembled into a hexagon 42.42 Å wide and 34.28 Å tall. Center and right panel: Spatial conductance maps recorded at constant tip height and the sample biases where the bonding and antibonding states of the quantum-dot dimer are observed in dI/dV spectra (not shown), confirming the symmetric and antisymmetric wave-function character, respectively.

In this project, we employ scanning tunneling microscopy (STM) at low temperatures to generate artificial quantum structures on semiconductor surfaces and investigate their electronic properties using scanning tunneling spectroscopy (STS). To create these structures, we have developed a highly controllable method of atom manipulation on the InAs(111)A surface. The pristine InAs(111)A surface has a surface state and positively charged indium adatoms that can be repositioned with the STM tip. This allows us to deliberately modify the electrostatic potential landscape and spatially confine charge carriers with atomic precision. We have shown that this method enables the creation of single quantum dots and quantum dot molecules with perfectly defined energy level structures. Additionally, we have constructed dimerized quantum dot chains that exhibit localized states at their ends and at internal domain walls, consistent with topological interface states predicted by the Su-Schrieffer-Heeger (SSH) model. Building on our previous work, we plan to address three main goals in the new project period:

  1. An in-depth analysis and complete description of the energy level structure of quantum dot molecules, taking into account hybridization effects beyond a simple s-orbital “tight-binding” model.
  2. Extension to artificial quantum dot arrangements on the InAs(110) cleaved surface; the larger terrace sizes should facilitate the construction of more extensive structures such as Kagomé lattices and two-dimensional analogs of the SSH model.
  3. STM/STS and atom manipulation on (110)-cleaved III–V semiconductor heterostructures with band edge design, where wide band gap layers are embedded in narrow band gap layers; we anticipate that results from this area will form the basis for future research aimed at realizing external electrodes for electrical control of the STM-generated quantum structures. Perfectly defined and tunable surface structures on semiconductors, as studied in this project, provide detailed insights into electron behavior in reduced dimensions. These findings are of significance for both fundamental research and future quantum technologies.

Funded by the Deutsche Forschungsgemeinschaft (DFG) - Project number 437494632

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