Magnetic impurities on superconductors present a viable platform for building advanced applications in quantum technologies. However, a controlled manipulation of their quantum states continues to pose a significant challenge, hindering the progress in the field. Here we show the manipulation of magnetic states in the radical molecule 4,5,9,10-tetrabromo-1,3,6,8-tetraazapyrene (TBTAP) on a Pb(111) superconducting surface using low-temperature scanning tunneling microscopy. Tunneling spectra reveal Yu-Shiba-Rusinov (YSR) states near the Fermi energy in isolated molecules. A quantum phase transition from singlet to doublet ground state is induced by changing the tip-molecule distance. Additionally, the presence of a second TBTAP molecule allows tuning of the YSR state position by altering the relative distance and can induce splitting of the YSR states for certain orientations. The construction of molecular chains up to pentamers shows periodic arrangements of charged and neutral molecules, with even-numbered chains forming a charged dimer structure at one end. Information can be encoded in these chains by switching the dimer position. These findings elucidate interactions between molecular assemblies and superconducting substrates, paving the way for advanced quantum-state engineering.
@article{arxiv.2408.05115,
title = {Nanoscale Control of Quantum States in Radical Molecules on Superconducting Pb(111)},
author = {Chao Li and Vladislav Pokorný and Martin Žonda and Jung-Ching Liu and Ping Zhou and Outhmane Chahib and Thilo Glatzel and Robert Häner and Silvio Decurtins and Shi-Xia Liu and Rémy Pawlak and Ernst Meyer},
journal= {arXiv preprint arXiv:2408.05115},
year = {2025}
}