Metal-Insulator Transition in Au Atomic Chains on Si with Two Proximal Bands

One-dimensional atomic chains on $\mathrm{A}\mathrm{u}/\mathrm{S}\mathrm{i}(557)$ feature two proximal 1D bands near the Fermi level, which were controversially attributed as a spinon-holon pair of a Luttinger liquid. Angle-resolved photoemission shows that only one band is metallic with the neighboring one gapped at room temperature. Furthermore, even the metallic branch is found to undergo a metal-insulator transition upon cooling, which follows a mean-field-type behavior. Scanning tunneling microscopy observes two apparently unequivocal chains on the surface, one of which exhibits periodicity doubling accompanying the metal-insulator transition. The surface 1D structure is thus concluded to be insulating at low temperature with a Peierls-type instability.

Figure 1

Two highly dispersive S1 and S2 bands of $\mathrm{A}\mathrm{u}/\mathrm{S}\mathrm{i}(557)$ at 300 K as shown (a) in the photoelectron intensity map in grey scale as a function of binding energy (as referenced to $E_F$) and momentum along the 1D chains $k_{\parallel }$ and (b) in the momentum distribution curves of the photoelectron intensity.

Figure 2

(a) Energy distribution curves (EDCs) of the photoemission intensity for the S1 and S2 bands at the two $k_F$ positions of 0.35 and $0.41{\mathrm{\AA }}^{\mathrm{-}\mathrm{1}}$, respectively, and (b) temperature dependence of the center-of-the-leading-edge positions of EDCs [see the arrows in (a)] for S1 and S2 at the corresponding $k_F$ positions. The EDC of a typical normal metal, Ta, is given for comparison in (a) and, due to the low intensity of S1 at $E_F$, its EDC in (a) is enlarged by a factor of 4.

Figure 3

Empty-state STM images at (a),(c) 300 and (d),(e) 78 K with a sample bias of (a),(d) $V_s=1.0$ and (c),(e) 0.7 V. The recent structural model of $\mathrm{A}\mathrm{u}/\mathrm{S}\mathrm{i}(557)$ [16, 17, 19] is shown in (b) schematically, where the large and small circles denote Au and Si atoms, respectively.

Figure 4

Temperature dependence of the energy gap of the S1 band is fitted with the mean field theory (dashed line), $\Delta (T)/\Delta (T=0)=(1-T/T_c{)}^{-1/2}$, where $T_c$ and $\Delta (T)$ are a critical temperature and an energy gap, respectively.