Defect-induced perturbation on $\mathrm{Si}\left(111\right)4\times 1\text{−}\mathrm{In}$: Period-doubling modulation and its origin

A one-dimensional defect-induced local period-doubling $(\times 2)$ modulation was observed with scanning tunneling microscopy on a $\mathrm{Si}\left(111\right)4\times 1\text{−}\mathrm{In}$ surface at room temperature. The $\times 2$ modulated region remains metallic in contrast to the low-temperature $4\times 2$ ground-state phase. First-principles calculations predict the lowest-energy state with exactly the same features as observed by H adsorption, but fundamentally different from the experimentally observed insulating ground state at low temperature. This suggests that the true ground state (i.e., the low-temperature phase) is not a band insulator, and is stabilized by many-body interaction.

Figure 1

STM images ($V_s=+0.2\mathrm{V}$, $I_t=0.1\mathrm{nA}$) with various types of defects: vacancy (V), step edge (SE), hydrogen adsorption (H), phase-shift boundary (PSB), and oxygen adsorption (O) or edge vacancy created by oxygen-induced etching (EV). Regardless of the defect types, there are $\times 2$ modulations in the vicinity of defects.

Figure 2

(top) STM images of the same region showing the bias-voltage dependence near H adsorbates indicated by arrow heads. (bottom) Line scans between two crosses in the $-0.2\mathrm{V}$ image. The position next to H and the $\times 2$ distances are marked by a solid line and dashed lines, respectively.

Figure 3

(a) $I\text{−}V$ data measured at points of unperturbed $\times 1$ and perturbed $\times 2$ rows. (b) An STM image acquired with $V_s=+10\mathrm{mV}$ and $I_t=0.17\mathrm{nA}$.

Figure 4

(a)–(c) Simulated STM images of the $4\times 1$-In surface with an H adsorbate in the $4\times 21$ supercell (parallelogram). The inset in (c) is the experimental counterpart of the H adsorbate. (d) Relaxed geometry around the H atom. A schematic in-plane relaxation pattern is represented by arrows. The interatomic distances between In atoms projected on the row direction is designated in $\mathrm{\AA }$. The projected inter-In distance is $3.86\mathrm{\AA }$ for the unperturbed $4\times 1$ surface.