Two distinct metallic bands associated with monatomic Au wires on the Si(557)-Au surface

Abstract

The Si(557)-Au surface, containing monatomic Au wires parallel to the steps, has been proposed as an experimental realization of an ideal one-dimensional metal. In fact, recent photoemission experiments on this system (Nature 402, 504 (1999)) found two peaks that were interpreted in terms of the spin-charge separation in a Luttinger liquid. Our first-principles density functional calculations reveal two metallic bands associated with Au-Si bonds, instead of the single band expected from the Au 6s states, providing an alternative explanation for the experimental observations. PACS Numbers: 73.20.At, 71.15.Mb, 71.10.Pm, 68.35.Bs It has been recognized for several decades now that a one-dimensional metal should considerably deviate from the Fermi liquid behavior [1][2][3][4]: quasiparticles would be replaced by two distinct collective excitations involving spin and charge, and some of the system's properties would exhibit characteristic power-law dependences. Despite this theoretical understanding, the experimental observation of the so-called Luttinger liquid behavior has proven quite elusive, due in large part to the lack of wellcharacterized one-dimensional systems. Only very recently, signatures of Luttinger liquid behavior have been observed by means of transport measurements in carbon nanotubes [5], in edge states of the fractional quantum Hall effect [6], and in quantum wires with a single conducting channel [7], and by optical conductivity measurements in organic conductors [8], and in the quasi-onedimensional CuO chains in PrBa 2 Cu 3 O 8 [9].More direct evidence of the Tomonaga-Luttinger behavior can be provided by angle-resolved photoemission experiments, in which the spin-charge splitting of the low-energy excitations can, in principle, be measured. This has been tried for several systems containing quasione-dimensional metallic chains [10,11]. However, in most cases the results were inconclusive due to the lack of energy and angular resolution [12], the difficulties to correctly align the chains, and other uncertainties associated with the crossover of dimensionality in the bulk samples. To avoid some of these problems, Segovia et al.[13] studied the photoemission from a monophase sample of the stepped Si(557)-Au surface, in which the gold atoms are believed to form single rows running parallel to the edge of each step. For this system, the measured spectra were assigned to a single one-dimensional band derived from the gold 6s states. The observed splitting of this band close to the Fermi level was interpreted in terms of the spin-charge separation in a one-dimensional electron liquid, providing the first direct measurement of two distinct peaks for spinons and holons. If such behavior is intrinsic to Au wires, it could also apply to monatomic gold wires fabricated using a scanning tunneling microscope (STM) and to mechanically controllable break junctions [14,15].In spite of this extraordinary observation, very little is still known about the atomic and the electronic structure of the Si(557)-Au s...

Systematic investigation of the structure of the Si(553)-Au surface from first principles

“…In particular, the vicinal Si͑557͒-Au surface reconstruction has been extensively studied in recent years, and its structure has been established from x-ray studies 10 and DFT calculations. 9,11,13 Similar to the case of the Si͑553͒-Au surface, the steps of Si͑557͒-Au run along the ͓110͔ direction and each terrace contains a monatomic chain of gold atoms. However, while for Si͑553͒-Au the surface normal is tilted from the ͓111͔ direction toward the ͓112͔ direction, the normal to the Si͑557͒-Au surface is tilted toward the opposite direction ͓͑112͔͒.…”

“…However, we are typically far from this ionic situation. The states of gold are strongly hybridized with those of the neighboring silicon atoms, which create several dispersive bands that are, in principle, metallic 9,11,13 and dominate the photoemission spectra.…”

“…18 The importance of the HC structure for the gold induced reconstructions on vicinal Si͑111͒ was recently emphasized by Crain et al 3 It is known to form the step edge of the Si͑557͒-Au surface. [9][10][11]16 It is also a key ingredient of the most recent proposals for the structure of the Si͑111͒-͑5 ϫ 2͒-Au reconstruction. 5,7 The HC structure was initially proposed to explain the low coverage reconstructions induced by some alkali metals ͑Li, Na, and K͒, Mg, and Ag on Si͑111͒.…”

“…Ab initio calculations indicate that the gold atoms prefer to occupy silicon substitutional positions in the middle of the terraces. 9,11,18 A good structural model is necessary to understand the physics of this system in detail. However, in contrast to the case of the Si͑557͒-Au surface, the structure of the Si͑553͒-Au reconstruction is not well established.…”

“…In the case of vicinal substrates, the average terrace width can be controlled by the miscut angle, which provides a route to tuning interwire distances and interactions. 3 Some examples of quasi-one-dimensional reconstructions that have attracted much attention in recent years are the Si͑111͒-͑5 ϫ 2͒-Au, [3][4][5][6][7] Si͑557͒-Au, [8][9][10][11][12][13][14][15][16] Si͑553͒-Au, [17][18][19][20][21][22][23][24] and Si͑111͒-͑4 ϫ 2͒-In ͑Refs. 25-37͒ surfaces.…”