Visualization of electronic topology in ZrSiSe by scanning tunneling microscopy

As emerging topological nodal-line semimetals, the family of $\text{ZrSi}X(X=\mathrm{S},\text{Se},\text{Te})$ 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 $\sim 300$ 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 $\sim 400$ meV below the Fermi level.

Figure 1

(a, b) Two $20\mathrm{nm}\times 20$ nm topographic images of ZrSiSe in the same FOV under a tunneling current of $I=400$ pA and bias voltages of $V_{\mathrm{b}}=500$ mV (a) and $V_{\mathrm{b}}=-500$ mV (b). (c) Enlargment of the local topographic images of two defects within red and yellow squares; upper and lower panels correspond to positive and negative bias voltages, respectively. (d) Average $dI/dV$ spectra at the top (yellow) and hollow (red) sites under $V_{\mathrm{b}}=-500$ mV. Inset: Schematic crystal structure of ZrSiSe.

Figure 2

(a) A $25\mathrm{nm}\times 25$ nm topographic image under $V_{\mathrm{b}}=500$ mV. (b) The $dI/dV(V=500$ mV) conductance map taken simultaneously with (a). (c, d) Enlarged images of (a) and (b) around a cross-shaped impurity labeled by the white arrow. (e) Experimental FT-STS map in the $\mathit{q}$ space using Fourier transform of the local conductance map in (d). (f) CCE model in $\mathit{k}$ space. (g) Calculated FT-STS map following this CCE model (see text). The typical scattering wave vectors responsible for the main QPI features are shown in (e)–(g).

Figure 3

In the FOV shown in Fig. 2, a series of $dI/dV$ conductance maps is measured and the FT-STS maps are analyzed. We show six typical FT-STS maps at varied voltages.

Figure 4

(a), (b) QPI energy dispersions along the dashed red and green lines in $\mathit{q}$ space [Fig. 2]. (c), (d) DFT calculation of the slab band structure along the M-$\mathrm{\Gamma }$-M and M-$X$-M directions in $\mathit{k}$ space [Fig. 2]. The DFT prediction of the topology-related scattering wave vectors is superimposed on (a) and (b).