Research staff from the Singular Research Centre in Biological Chemistry and Molecular Materials of the USC (CiQUS), in collaboration with the Quantum Detection Microscopy group at CIC nanoGUNE, have published in the journal Nature the results of a study revealing how the parity of a quantum chain, meaning whether it contains an even or odd number of units, can alter its interaction with a superconductor. Chains with an odd number interact magnetically, while even-numbered ones do not.
The chains are formed by triangulenes, triangular graphene fragments with spin (S=1). When linked, their spins form a Haldane phase, which develops fractional spin states (S=1/2) at its ends. The study focused on what happens when these fractional states come into contact with a superconductor.
To overcome the experimental challenge of fabricating these nanostructures on superconducting surfaces, the researchers developed a platform combining a film of gold (25-30 atomic layers) on niobium. This structure acquires superconductivity due to its proximity to niobium, retaining the chemical environment of gold and the electronic properties of a superconductor.
Measurements using scanning tunneling microscopy and spectroscopy confirmed the parity effect: odd-numbered chains showed magnetic interaction with the superconductor, while even-numbered ones did not, highlighting the decisive role of the number of units.
Diego Peña, Oportunius Research Professor and leader of the CiQUS team, stated that "this work is an example of how the research we develop at CiQUS contributes to the advancement of quantum technologies, combining molecular design, chemical synthesis, and surface physics for the study of emergent quantum properties".
Nacho Pascual, Ikerbasque Professor at nanoGUNE, added that "magnetic molecules are candidates for quantum bits, and a superconductor offers an environment to read them and protect them from noise." He explained that the results show a method to "turn on or off the interaction of the chains with the superconductor by changing their length by a single unit," establishing a platform to combine the construction of atomic-precision molecular materials with superconductivity.
The work was funded by projects such as MOLSENSE, CONSPIRA, and MolDAM. CIC nanoGUNE and CiQUS have received accreditations as María de Maeztu Units of Excellence and have support from the Xunta de Galicia and the European Union.
