Odd-parity ground state in dilute Yu-Shiba-Rusinov dimers and chains

Magnetic adatoms on superconductors induce Yu-Shiba-Rusinov (YSR) states, which are key to the design of low-dimensional correlated systems and topological superconductivity. Competing magnetic interactions and superconducting pairing lead to a rich phase diagram. Using a scanning tunneling microscope (STM), we position Fe atoms on <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mn>2</a:mn><a:mi>H</a:mi><a:mtext>−</a:mtext><a:msub><a:mi>NbSe</a:mi><a:mn>2</a:mn></a:msub></a:mrow></a:math> to build a dimer with an odd-parity ground state, i.e., a partially screened YSR channel with the hybridized states spanning the Fermi level. This ground state makes the dimer a promising precursor for a topological YSR chain. By adding one atom at a time, we track the formation of YSR bands. The lowest-energy band crosses the Fermi level, and we find strong site-dependent spectral variations especially at the chain's terminations. We attribute these features to quantum spin effects and ferromagnetic coupling influenced by the local chemical environment.