Visualization of electronic topology in ZrSiSe by scanning tunneling microscopy

As emerging topological nodal-line semimetals, the family of ZrSiX (X = S, Se, Te) has attracted broad interest in condensed matter physics due to its future applications in spintronics. Here, we apply scanning tunneling microscopy to study the structural symmetry and electronic topology of ZrSiSe. Bias selective topographies are detected and applied to quantify the lattice structure of the ZrSe bilayer. A quasiparticle interference analysis is used to probe the band structure of ZrSiSe. We observe the mergence of two concentric squares similar to 300 meV above the Fermi level, which shows a nodal-line state consistent with a first principle calculation. An extra surface-state Dirac point is determined similar to 400 meV below the Fermi level.