To achieve this objective, a progressive plan is devised, starting from studying simple superconducting substrates to adsorbed magnetic atoms on superconducting surfaces using STM.
First of all, before manipulating the atoms on superconductor, we studied magnetic Mn chains built on one thin insulating layer (Cu2N) ontop of metal surface Cu(100). Atomic magnetic chains are very interesting objects that reveal the complexities of quantum magnetic interactions. Thanks to the advances in low-temperature STM, these objects have been created and studied with unprecedented precision. In this work, we disclose our discovery of electronic edge states in Mn magnetic chains and that their behaviour has bearing on the actual magnetic ordering of the atomic chains. We characterise the edge states to find that they are associated with an orbital on each of the two edge Mn atoms and that their character depends on the number of Mn atoms in the chain. We show that this odd/even behaviour is a consequence of the magnetic ordering of the chain.
As a next step, using well-know type I-superconducting substrate lead (Pb), we investigated single magnetic atoms such as Fe and Cr. We observed exotic properties like Shiba states which are coming from the magnetic moment in a quasi-particles (Cooper pairs). This magnetic impurity on a superconductor forms a magnetic scattering potential due to the breaking of Cooper pair. The Shiba state has been seen on Cr atoms inside the superconducting gap. And by doing dI/dV mapping at the certain energies, we manage to see the orbital contribution which originates the Shiba states.
Furthermore, we used type II-superconductor Bi2Pd as a substrate and studied single magnetic impurities eventually to build the atomic chains. First we tried with Fe atoms and basically Fe atoms quench the superconductivity of Bi2Pd. So we deposit other kinds of atoms such as Mn, Cr and Co atoms. We are creating atomic chains by manipulating atoms with intrinsic magnetic moments on Bi2Pd surfaces. We are able to map out what kind of orbitals contribute to form Shiba states by measuring the dI/dV maps at the certain energies. The Shiba states are quasi-particle localized states at a magnetic impurity due to the exchange interaction between the magnetic moment of the atomic chain and the electronic spin from the substrate. The atomic magnetic moment acts as a classical magnet that simply scatters the electrons. The existence of a gap at the Fermi energy due to the superconductor pairing leads to the localization of the scattered electrons and a single quasi-particle peak appears in the gap in the dI/dV spectra.
