Effect of substrate spin-orbit coupling on the topological gap size of Shiba chains

Abstract

Realizing Majorana bound states in chains of magnetic impurities on s-wave superconducting substrates relies on a fine tuning of the energy and hybridization of the single magnetic impurity bound states and of the spin-orbit coupling (SOC). While recent experiments investigate the influence of the former two parameters, the effect of SOC remained experimentally largely unexplored.Here, we present a scanning tunneling spectroscopy study of close-packed Mn chains along the [001]direction on Ta(110) which has almost identical atomic and surface electronic structure compared to the previously studied Nb(110) system, but a three times larger SOC. The dominant Shiba band has a very similar dispersion, but its minigap, taken relative to ∆, is increased by a factor of 1.9 with respect to the Nb case, which can be ascribed to the stronger SOC.

Systematic study of Mn atoms, artificial dimers and chains on superconducting Ta(110)

“…The measurements shown in this publication and its accompanying manuscript [32] were performed in a homebuilt ultrahigh vacuum (UHV) STM system [33], consisting of three chambers: One designated preparation chamber, containing a home-built e-beam heater for high temperature flashes, another chamber containing a system for low-energy electron diffraction (LEED) measurements and a chamber connected to an UHV wet cryostat including a 3 He refrigerator, which hosts an STM oper- ated at a temperature of 320 mK in a magnetic field up to 12 T perpendicular to the sample surface. We used a mechanically sharpened superconducting Nb tip for all measurements to obtain an improved energy resolution by overcoming the Fermi-Dirac distribution limit at finite temperatures, which regular metal tips would usually impose on the experiment [34].…”

“…1(d By further increasing the flashing power to 380 W we obtain a clean Ta(110) surface which is merely covered by 6% of oxygen impurities (overview STM image in Ref. [32]). This sample was used for all subsequent experiments with Mn and Fe adatoms and their artificial structures.…”

“…Both depositions were carried out while maintaining a sample temperature < 6 K to achieve statistically distributed single adatoms (overview image in Ref. [32] and Fig. 3(a), see below).…”

“…III F) and in Ref. [32]. Last, we perform spin-polarized (SP)-STM with YSR-functionalized superconducting tips (Sec.…”

“…III E) to measure the spin structures of both chains (that of the [001]-direction can be found in Ref. [32]), which show indications for a dominating ferromagnetic order.…”