Superconductivity near the saddle point in the two-dimensional Rashba system Si(111)-$\sqrt{3}\times \sqrt{3}$-(Tl,Pb)

Abstract

Two-dimensional Rashba superconductor Si(111)-$\sqrt{3}\times \sqrt{3}$-(Tl,Pb) is a candidate platform of mixed spin-singlet and -triplet superconductivity. A recent scanning tunneling microscope (STM) experiment revealed a pseudogap at the vortex core, suggesting the finite triplet component [T. Nakamura $\text{et al.}$, Phys. Rev. B $98$, 134505 (2018)]. Detailed spectroscopic information of the superconducting gap and the low-energy band structure is necessary to establish the putative triplet superconductivity. Here, we performed high-energy-resolution spectroscopic imaging experiments on Si(111)-$\sqrt{3}\times \sqrt{3}$-(Tl,Pb) using an ultra-low temperature STM. We found that various spectroscopic features, including the vortex-core spectrum, are consistent with spin-singlet $s$-wave superconductivity, having no sign of the triplet component. The apparent contradiction with the previous STM result suggests that the nature of superconductivity changes within the same system. From the analysis of the quasiparticle interference patterns, we found that the Fermi energy is in the close vicinity of the saddle point near the $\overline{\mathrm{M}}$ point. We speculate that the nature of superconductivity varies depending on the saddle-point energy with respect to the Fermi energy, which is sample-dependent due to different band filling.

23 pages, 7 figures

References in corpus (9)

• Signatures of Majorana fermions in hybrid superconductor-semiconductor nanowire devices
• An Intrinsic Bond-Centered Electronic Glass with Unidirectional Domains in Underdoped Cuprates
• Topological Phases of Noncentrosymmetric Superconductors: Edge States, Majorana Fermions, and the Non-Abelian Statistics
• Zero-energy vortex bound state in the superconducting topological surface state of Fe(Se,Te)
• Imaging Josephson Vortices on the Surface Superconductor Si(111)-(root7xroot3)-In using a Scanning Tunneling Microscope
• Atomic-layer Rashba-type superconductor protected by dynamic spin-momentum locking
• Spin-orbit scattering visualized in quasiparticle interference
• Chiral topological superconducting state with Chern number $\mathcal{C}=-2$ in Pb${}_3$Bi/Ge(111)
• Removing background and estimating a unit height of atomic steps from a scanning probe microscopy image using a statistical model

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