The Philosophy of the Scanning Tunnelling Microscope

M. Kleber, Christian Bracher, M. Riza

R. Werner, Hofer

Ranko Toskovic

Physics at the level of an atom is dominated by laws of quantum mechanics. Often, this is entangled with a high complexity in behavior of the systems at that length scale. Unravelling the properties of a material at the atomic level is, therefore, a challenging task that easily supersedes current computational capabilities. A route to circumvent this problem is found in physical realization of simpler quantum systems that are representative of the complex quantum systems one is interested in. These simpler physical systems, unlike their more complex counterparts, can actually be measured and information about the complex system, otherwise inaccessible, gained. This thesis describes experimental work focusing mainly on the property of magnetism in spin chains. To mimic these complex systems, we employ a scanning tunneling microscope (STM) to build atomic chains on solid state surfaces and probe their magnetic properties. The intrinsic strength of STM in building and testing structures with single atom precision makes STM a great candidate for simulation of complex quantum systems. In addition to STM having a role of a quantum simulator, I present work supporting STM as a control device determining the very existence of the magnetic excitations of the atom it measures. Finally, I present experimental findings that suggest we are able to probe the magnetic excitations of the atom with subatomic resolution. In summary, this thesis work presents STM as a powerful probing and control tool for studies on quantum magnetism at the level of a single atom.

Mei‐Ling Feng, Guofeng Dong, Biaoyan Hu

We consider the detection of the electron spin of a doped atom, i.e., nitrogen or phosphorus, caged in a fullerene by the currently available technique of the scanning tunnelling microscope (STM), which actually corresponds to the readout of a qubit in fullerene-based quantum computing. Under the conditions of polarized STM current and Coulomb blockade, we investigate the tunnelling matrix elements involving the exchange coupling between the tunnelling polarized electrons and the encapsulated polarized electron, and calculate the variation of the tunnelling current with respect to different orientations of the encapsulated electron spin. The experimental feasibility of our scheme is discussed taking account of some imperfect factors.

N. D. Lang

Zhihua LIU, Siyuan LYU, Meng Ran Zhou +1 more

The plasmon cavity system composed of a scanning tunneling microscope tip and a substrate has attracted much attention due to its ability to break through the diffraction limit, enhance the electromagnetic field by hundreds of times, and localize it on a nanometer or even sub-nanometer scale. This plasmon cavity system can serve as an advanced platform for studying superradiance phenomena on an ultrafast scale. Methylene blue molecules have many applications in the field of optics due to their significant light absorption and fluorescence emission characteristics. In this work, macroscopic quantum electrodynamics and open quantum system theory are used to explore the radiation dynamics of methylene blue molecular clusters with three different configurations: cyclic, two-dimensional planar, and one-dimensional chain, in specific scanning tunneling microscope nanocavity and picocavity. Taking the cyclic molecular clusters for example, the radiation effects of different external field excitations on the molecular clusters in the cavity are studied. The research results indicate that for the same molecular cluster configuration, the scanning tunneling microscope picocavity has a more significant superradiance intensity, while the scanning tunneling microscope nanocavity has a longer duration of superradiance. From the perspective of symmetry, the one-dimensional chain molecular clusters only have axial symmetry, while the two-dimensional planar and cyclic molecular clusters have both axial symmetry and central symmetry. The cyclic molecular clusters also have multiple rotational symmetries. Therefore, within the same scanning tunneling microscope cavity, the higher the symmetry of the arrangement of molecular clusters, the easier it is to generate significant superradiance pulses. In addition, because of its higher spatial resolution and stronger local field enhancement effect, the picocavity of scanning tunneling microscope is more sensitive to changes of external conditions such as excitation wavelength. These results indicate that the occurrence and enhancement of superradiance can be effectively controlled by reasonably designing the cavity structure and geometric configuration of molecular clusters, and the time scale of superradiance pulses can be extended to the picosecond order, which provides new ideas and methods for practical applications in the fields of optics and nanotechnology in the future.