Large dispersion of incoherent spectral features in highly ordered ${\mathrm{C}}_{60}$ chains

Large dispersion of incoherent spectral features in highly ordered $C_{60}$ chains

A. Tamai, A. P. Seitsonen, T. Greber, and J. Osterwalder

Phys. Rev. B 74, 085407 – Published 15 August 2006

Abstract

Ordered one-dimensional $C_{60}$ chains on a vicinal Cu template were studied by angle-resolved photoemission. A complete structural model for $C_{60}$ on Cu(553) is proposed, where two differently coordinated and oriented $C_{60}$ molecules self-assemble in chains along the steps of the vicinal substrate. The highest occupied molecular orbital–derived peak shows a broad Gaussian line shape with features dispersing up to $400 meV$ along the chains. The line shape is interpreted in terms of a strong electron-phonon interaction leading to the formation of polarons with a spectral function dominated by incoherent multiphonon excitations. The large dispersion of this incoherent peak derives from a particularly favorable relative orientation of the molecules and is in good agreement with the one-electron band structure calculated by density functional theory, which indicates that the photoelectrons carry some memory of the frozen lattice.

Received 6 December 2005

DOI:https://doi.org/10.1103/PhysRevB.74.085407

Authors & Affiliations

A. Tamai^1,*, A. P. Seitsonen^2,†, T. Greber¹, and J. Osterwalder¹

¹Physik Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
²Physikalisch Chemisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland

^*Present address: School of Chemistry and Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh EH9 3JZ, UK. Electronic address: anna.tamai@ed.ac.uk
^†Present address: CNRS & IMPCMC, Université Pierre et Marie Curie, 4 place Jussieu, F-75252 Paris, France.

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Vol. 74, Iss. 8 — 15 August 2006

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Figure 1
(a) Room-temperature STM image ( $100 \times 100 Å^{2}$ , $- 1.5 V$ sample bias, $1 nA$ tunneling current). (b) Experimental C $1 s$ XPD pattern (Mg $K α$ , $E_{kin} = 970 eV$ ). The direction of the substrate along the step and the terrace normal are indicated. (c) SSC calculations for pentagon- and hexagon-bonded $C_{60}$ molecules superimposed with equal weight. (d) Suggested real space model for the $C_{60}$ chains on the unit cell of Cu(553). Top view along [111]. The crossed markers show the different coordination to the copper atoms of the step for $C_{60}$ molecules of adjoining chains.Reuse & Permissions
Figure 2
Normal emission valence band spectrum with fits of the low-energy side of the HOMO peak to a Lorentzian (dashed line) and a Gaussian (full line).Reuse & Permissions
Figure 3
(Color online) (a) Sketch of the $C_{60}$ Brillouin zone and scan directions of the azimuthal cut $A$ and the polar cut $B$ , shown in (d) and (e), respectively. The azimuthal cut is measured at a polar angle of 44° around $[\bar{3} \bar{3} 10]$ $(ϕ = 0 °)$ . The polar cut is along $[\bar{3} \bar{3} 10]$ , the direction perpendicular to the $C_{60}$ chains. (b) and (c) Sets of energy distribution curves measured along the azimuthal cut $A$ and along the polar cut $B$ , respectively. (d) and (e) Angular intensity distribution maps along the azimuthal cut $A$ and the polar cut $B$ . The photoemission intensity is displayed on a linear gray scale with black at maximum intensity.Reuse & Permissions
Figure 4
DFT-LDA calculations of the $h_{u}$ (HOMO) band structure for $C_{60}$ chains in a free-standing layer. The distance between the molecules is set to the experimental values. The energy scale has been shifted for a comparison with the experiment (see text). (a) and (b) Chains of molecules sitting on the pentagon and on the hexagon, respectively. Insets: top view along the chains. (c) Band dispersion for the dual chain structure. The solid line emphasizes the band with the largest dispersion.Reuse & Permissions
Figure 5
HOMO width $Γ (k)$ (FWHM) as a function of the peak position $ϵ (k)$ from $\bar{Γ}$ to $\bar{Y}$ .Reuse & Permissions
Figure 6
(Color online) (a) Fit to the angle-resolved spectra with two Gaussian components after background subtraction. (b) Quasiparticle (QP) dispersion as determined by the onset of the peak (dots). Positions of the two Gaussians from the fit (squares and circles). The dash-dotted line indicates the center of gravity of the nine DFT bands that disperse less than $200 meV$ . The DFT band with the largest dispersion is projected on the same azimuthal scan (full line).Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Large dispersion of incoherent spectral features in highly ordered $C_{60}$ chains

A. Tamai, A. P. Seitsonen, T. Greber, and J. Osterwalder

Phys. Rev. B 74, 085407 – Published 15 August 2006

Abstract

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Physical Review B

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Large dispersion of incoherent spectral features in highly ordered C60 chains

A. Tamai, A. P. Seitsonen, T. Greber, and J. Osterwalder

Phys. Rev. B 74, 085407 – Published 15 August 2006

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Large dispersion of incoherent spectral features in highly ordered $C_{60}$ chains