Electrons have the smallest possible spin that can take two discrete values, while the next simplest systems are those whose spin takes three discrete values – these are dubbed spin ½ and spin 1, respectively. In the 1980s, it was predicted that a one-dimensional chain of interacting spin 1 units should be 'fractionalized', such that the terminal units of the chain behave, counterintuitively, like spin ½ objects. Therefore, much like magicians who seem to saw a person in two halves and pull them apart, quantum correlations in the chain divide a spin 1 in two spin ½ entities.
Testing this prediction in a laboratory has been challenging for various reasons, chief among them being that conventional materials are not one-dimensional. While indirect evidence of spin fractionalization has been seen in crystals of organometallic chains containing transition metal ions, a direct observation of the phenomenon has remained elusive.
Now, an international team of researchers has found a remarkable route to accomplish this feat. Combining organic chemistry and ultra-high vacuum surface science, the team fabricated chains of a triangular polycyclic aromatic hydrocarbon with spin 1, known as triangulene. Using a scanning tunneling microscope the team then probed magnetic excitations of these spin chains on a gold surface. They found that beyond a certain length, the terminal triangulene units of the chains exhibited Kondo resonances – which are a characteristic spectroscopic fingerprint of spin ½ quantum objects in contact with a metal surface.
The researchers are convinced that easily and directly accessible molecular spin systems exhibiting strongly correlated behavior of electrons will become a fertile playground for developing and testing new theoretical concepts. In addition to exploring linear spin chains, the scientists are also focusing on two-dimensional networks of quantum magnets. Such spin networks are a promising material platform for quantum computation.
COMPAMED-tradefair.com; Source: Empa
