Recent Publications

The geometrical structure of clusters highly depends on the number of atoms and their composition. Eletric and magnetic beam deflection experiments can help discriminating geometrical structures calculated by quantum chemistry and give insight into electric and magnetic properties of the clusters.

It was observed for the magnetic and electric beam deflection of the Sn₁₂Al clusters that two fractions each are present in the molecular beam resulting from either hot and cold clusters or two different isomers. To investigate this further, a combination of both experiments was implemented in which the clusters first pass the inhomogeneous eletric field. With this, the polar fraction can be filtered out and only the non-polar fraction passes the following inhomogeneous magnetic field.

The magnetic beam deflection of the now mostly non-polar fraction showed a decrease in only one of the magnetic fractions. Therefore, a direct connection of the electric and magnetic properties of the Sn₁₂Al clusters can be concluded. Furthermore, the results clearly suggest that two isomers are responsible for the presence of two fractions.

The investigation of the beam profiles measured with different nozzle temperatures enabled a further evaluation of the influence of the thermal excitation of the Sn₁₂Al clusters.

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For macroscopic objects, temperature is a uniquely defined, intensive state variable. However, for isolated metal clusters, consisting of only a few atoms and not in contact with a heat bath, the description of thermal excitation by a temperature is not straightforward. However, the thermal excitation fundamentally affects various experiments, so quantification is necessary. After their generation by laser evaporation with a carrier gas, the clusters are adiabatically expanded into high vacuum through a nozzle, where cooling occurs. The cooling efficiency varies for the different degrees of freedom and there is no heat exchange between the degrees of freedom as soon as the clusters enter high vacuum, so different temperatures are necessary for each degree of freedom.

In this publication, by measuring the velocity distribution of the clusters as well as deflection experiments in inhomogeneous electric and magnetic fields, the different temperatures of the clusters were estimated. In agreement with previous work on dimers and trimers, it has now been shown also for larger clusters, that translation and rotation of the investigated clusters are colder than the vibrations. The figure to the right shows these temperatures for different nozzle temperatures T_nozzle.

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Quantum states with a long lifetime are an important prerequisite for applications in quantum information processing and data storage technology. Typical examples of such systems are solids with spin centers that can be introduced by doping atoms. An Sn₁₂Al cluster, in which an aluminum atom is surrounded by a highly symmetric cage of 12 tin atoms, can be regarded as the smallest possible building block of a p-doped tetrel. Isolated from external influences, this model system is ideally suited to study the dependence of magnetic properties on the composition of the tin cage, i.e., the first coordination sphere around the electron acceptor.

Molecular beam experiments on isolated metal clusters of precisely defined size and composition in high vacuum allow to study the intrinsic properties of these species without a solvent or a substrate. Deflection experiments in inhomogeneous magnetic fields according to Stern and Gerlach provide an approach to the magnetic moments of the clusters. In this publication, the dependence of the spin dynamics of the spin-1/2 system Sn₁₂Al on the number of nuclear spins was studied in double deflection experiments with isotope-enriched samples. It was observed that an increase in the number of nuclear spins on the tin cage lead to increased spin flips. This observation was attributed to spin-rotation coupling by numerical simulation of the spin dynamics based on the time-dependent Schrödinger equation. This type of experiment will be performed in the future for clusters of different sizes and compositions to better understand the spin dynamics and prepare future applications of tailored clusters.

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