Coupled Pb Chains on Si(557): Origin of One-Dimensional Conductance

Abstract

The Pb=Si557 system exhibits a strong anisotropy in conductance below 78 K, with the evolution of a characteristic chain structure. Here we show, using angle-resolved photoemission, that chain ordering results in complete Fermi-like nesting in the direction normal to the chains; in addition, the domain structure along the chains forms split-off valence bands with mesoscopic Fermi wavelengths which induce the 1D conductance without further instabilities at low temperatures. DOI: 10.1103/PhysRevLett.100.076802 PACS numbers: 73.20.At, 68.65.ÿk, 73.21.ÿb, 73.25.+i Confinement of electrons in low-dimensional structures induces intriguing transport phenomena and electronic properties. This scenario of strongly interacting electrons is described within the framework of a Luttinger liquid (LL) rather than by a Fermi liquid (FL) [1]. In an intuitive picture, this changeover is intimately related to the geometry of the structure; i.e., the interaction between electrons is enhanced in low-dimensional systems. An obvious strategy of making one-dimensional (1D) conductors is to use anisotropic solid state bulk materials like Bechgaard salts [2,3] or, as shown recently, Ca 2 Ru 2 O 7 [4,5]. Anisotropic adsorbate structures, realized on (vicinal) surfaces, are even more flexible, because the structure can be controlled on an atomic scale, and the electronic structure can be changed gradually by varying the degree of localization, e.g., by changing terrace widths. Submonolayer coverages of Ag and Au on vicinal Si(111) surfaces form chain structures showing indeed localized states perpendicular to the chain direction [6 -8]. However, these weakly interacting systems often undergo instabilities, e.g., Peierls-or Mott-Hubbard driven phase transitions into insulating states at low temperature (see, e.g., [9] ), and the 1D character of charge carriers is rarely established in transport measurements.The Pb=Si557 system is unique in this respect since macroscopic conductance measurements [10,11] reveal a slightly anisotropic temperature activated conductance above T c 78 K. Below this temperature the conductance switches reversibly to quasi-1D and metallic along the step direction, while in the perpendicular direction conductance is indistinguishable from the residual conductance of the substrate. In contrast to all systems exhibiting quasi 1D-conductance properties investigated so far, this system turns into a quasi-1D metallic conductance state at low temperatures with no indications of further instabilities.This intriguing behavior requires an explanation in terms of the interplay of the geometric and electronic structure across the phase transition. Here using angleresolved photoemission (ARPES), we demonstrate that the interplay of the overlayer structure and the substrate leads to an electronically stabilized arrangement of chain structures and has direct consequences on the formation and filling of electronic bands that results in the observed transport properties. In particular, we demonstrate 1D conductance is a direct co...

Fermi Nesting between Atomic Wires with Strong Spin-Orbit Coupling

“…2c) and the momentum distribution curve shown in Fig. 2e) the reciprocal lattice vector g = 2π/d = 0.4Å −1 is defined by the interwire distance d=1.58 nm in agreement with former studies [13,22]. Qualitatively, the complex contour close to E F can be explained by replicas of circles, which reflects the local 2D character of the densely packed α − √ 3 × √ 3 phase of Pb on the mini-(111) terraces (cf.…”

“…Details can be found in Ref. [13]. Besides the intense Umklapp structure the constant energy map (see arrows) as well as the spin-integrated MDC, both taken 100 meV below E F , reveal a substructure which is less in intensity and shifted by around 0.2Å −1 with respect to the dominant replica structure.…”

“…as seen for Pb/Si(557). For this system, strong coupling of adjacent wires has revealed 1D transport due to Fermi nesting in the direction across the wires, however, the role of SOC in this system was not taken into account so far [12,13].…”

“…2a). Details about the preparation and coverage calibration are reported elsewhere [13]. The photoemission experiments were performed with p-polarized light (mostly hν = 24eV) at 60 K at a base pressure of 1 × 10 −8 Pa. By recording intensities and spin-induced scattering asymmetries with the two orthogonal Mott detectors for different emission angles, spin-resolved momentum distribution curves (MDCs) close to the Fermi energy have been measured.…”

Modeling 1D structures on semiconductor surfaces: synergy of theory and experiment

“…Also Pb on Si(557) gives rise to conducting NWs, with quasi-1D states below a critical temperature of 78K; above this critical temperature the two dimensional (2D) coupling of the NWs makes the Pb chains 2D conducting. [47][48][49] A different kind of NWs are the Bi nanolines on Si(001). These reconstructions are not metallic, but one of the few examples of atomically perfect 1D systems on Si.…”