Mechanism of Gap Opening in a Triple-Band Peierls System: In Atomic Wires on Si

One dimensional (1D) metals are unstable at low temperature undergoing a metal-insulator transition coupled with a periodic lattice distortion, a Peierls transition. Angle-resolved photoemission study for the 1D metallic chains of In on Si(111), featuring a metal-insulator transition and triple metallic bands, clarifies in detail how the multiple band gaps are formed at low temperature. In addition to the gap opening for a half-filled ideal 1D band with a proper Fermi surface nesting, two other quasi-1D metallic bands are found to merge into a single band, opening a unique but $k$-dependent energy gap through an interband charge transfer. This result introduces a novel gap-opening mechanism for a multiband Peierls system where the interband interaction is important.

Figure 1

Atomic structure models of the metallic $4\times 1$ phase (a) and the insulating CDW $4\times 2$ phase (b) [7], where unit cells are drawn by the dotted lines, and the arrows in (b) indicate the major displacements of the In atoms at LT. Schematic drawings of the triple bands in the metallic state with the nesting vector (${\mathrm{q}}_{\mathrm{C}\mathrm{D}\mathrm{W}}$) (c) and the insulating CDW state (f) as measured in our experiment. The simple band structures expected by $\times 2$ PLD/CDW within the simple single-gap (d) and triple-gap (e) pictures.

Figure 2

Measured energy bands of In/Si(111) along the wires ($k_{\parallel }$) in the metallic state (RT) at two different $k_{\perp }$'s of 0 (a) and $0.24{Å}^{-1}$ (c) and in the insulating state (45 K) (b),(d). Constant-energy spectral density maps at $E_F$ showing the Fermi contours for the metallic states (e) and at a binding energy of 0.1 eV for the valence band maxima of the insulating phase (f), which are schematically depicted in (g) and (h), respectively. The first BZ of the $4\times 1$ phase is drawn by the thin solid lines in (g). The wiggling Fermi contours (g) and the varying band dispersions at different $k_{\perp }$'s (a),(c) of $m_1$ and $m_2$ manifest the deviation from an ideal 1D nature in contrast with $m_3$.

Figure 3

Measured energy bands (b)–(d) along the In wires ($k_{\parallel }$) at 45 K at different $k_{\perp }$'s indicated in (a). The band backfolding position and the size of the band gap of $m_2^{\prime }$ vary over $k_{\perp }$, as indicated by the white bars and dashed arrows, respectively, in contrast with those of $m_3^{\prime }$.

Figure 4

Measured dispersions of the $m_2$ band along the interwire direction ($k_{\perp }$) at the metallic state (a) and the insulating CDW state (b) at $k_{\parallel }=0.53{Å}^{-1}$, which are schematically drawn in (c) and (d). The first BZ's of the $\times 4$ and $\times 8$ orders are indicated by the shaded rectangles in (c) and (d), respectively.