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Scanning tunneling microscopy of the charge density wave in 1T−TiSe2 in the presence of single atom defects

A. M. Novello, B. Hildebrand, A. Scarfato, C. Didiot, G. Monney, A. Ubaldini, H. Berger, D. R. Bowler, P. Aebi, and Ch. Renner
Phys. Rev. B 92, 081101(R) – Published 4 August 2015
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    Abstract

    We present a detailed low-temperature scanning tunneling microscopy (STM) study of the commensurate charge density wave (CDW) in 1T−TiSe2 in the presence of single atom defects. We find no significant modification of the CDW lattice in single crystals with native defect concentrations where some bulk probes already measure substantial reductions in the CDW phase transition signature. A systematic analysis of STM micrographs combined with density functional theory modeling of atomic defect patterns indicate that the observed CDW modulation lies in the Se surface layer. The defect patterns clearly show there are no 2H-polytype inclusions in the CDW phase, as previously found at room temperature [A. N. Titov et al., Phys. Solid State 53, 1073 (2011)]. They further provide an alternative explanation for the chiral Friedel oscillations recently reported in this compound [J. Ishioka et al., Phys. Rev. B 84, 245125 (2011)].

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    • Received 9 February 2015

    DOI:https://doi.org/10.1103/PhysRevB.92.081101

    ©2015 American Physical Society

    Authors & Affiliations

    A. M. Novello1,*, B. Hildebrand2,†, A. Scarfato1, C. Didiot2, G. Monney2, A. Ubaldini1, H. Berger3, D. R. Bowler4, P. Aebi2, and Ch. Renner1

    • 1Department of Quantum Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland
    • 2Département de Physique and Fribourg Center for Nanomaterials, Université de Fribourg, CH-1700 Fribourg, Switzerland
    • 3Institut de Génie Atomique, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
    • 4London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom

    • *Corresponding author: anna.novello@unige.ch
    • †Corresponding author: baptiste.hildebrand@unifr.ch

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    Vol. 92, Iss. 8 — 15 August 2015

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    • Figure 1
      Figure 1

      Simultaneously measured empty-state [(a) Vbias=0.15V] and filled-state [(b) Vbias=−0.15V] STM micrographs of a 1T−TiSe2 single crystal grown at 650 ∘C. Image size: 22.2 nm×11.4nm,It=0.2nA,T=4.7K. Native defects are labeled A, B, C, and D.

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    • Figure 2
      Figure 2

      (a) Ball-and-stick model of the 1T−TiSe2 lattice showing the positions of the native defects A–D. (b) Model representation of the inequivalent 1/4 (solid symbols) and 3/4 (open symbols) lattice sites for defects A–D in the commensurate CDW phase.

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    • Figure 3
      Figure 3

      High-resolution STM micrographs centered on Se vacancies [(a), (b)], iodine [(d), (e)] and oxygen [(g), (h)] substitutions at 3/4 sites [(a), (d), (g)] and 1/4 sites [(b), (e), (h)] with corresponding DFT simulations calculated without including the CDW [(c), (f), (i)]. (j) Linear features around defects A and B observed by STM on 1T−TiSe2 grown (11.5×11.5nm2, Vbias=+150mV, It=0.2nA). All images are taken on crystals grown at 650 ∘C, except for image (j) recorded on a sample grown at 575 ∘C to have a reduced number of intercalated Ti.

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    • Figure 4
      Figure 4

      High-resolution STM micrographs centered on intercalated Ti at 3/4 sites [(a), (e)] and 1/4 sites [(c), (g)] with corresponding DFT simulations in the presence of the CDW [(b), (d), (f), (h)]. (a)–(d) Vbias=−150mV and (e)–(h) Vbias=+150mV, It=0.2nA.

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