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Insight into the Charge Density Wave Gap from Contrast Inversion in Topographic STM Images

Published inPhysical Review Letters, vol. 125, no. 267603
Publication date2020
Abstract

Charge density waves (CDWs) are understood in great detail in one dimension, but they remain largely enigmatic in two-dimensional systems. In particular, numerous aspects of the associated energy gap and the formation mechanism are not fully understood. Two long-standing riddles are the amplitude and position of the CDW gap with respect to the Fermi level (EF) and the frequent absence of CDW contrast inversion (CI) between opposite bias scanning tunneling microscopy (STM) images. Here, we find compelling evidence that these two issues are intimately related. Combining density functional theory and STM to analyze the CDW pattern and modulation amplitude in 1T-TiSe2, we find that CI takes place at an unexpected negative sample bias because the CDW gap opens away from EF, deep inside the valence band. This bias becomes increasingly negative as the CDW gap shifts to higher binding energy with electron doping. This study shows the importance of CI in STM images to identify periodic modulations with a CDW and to gain valuable insight into the CDW gap, whose measurement is notoriously controversial.

Keywords
  • Charge density waves
  • Scanning tunneling microscopy
  • Charge density wave gap
  • TiSe2
  • Condensed matter physics
  • Electronic properties
Research group
Funding
  • Swiss National Science Foundation - Div. II (Grant No. 162517)
Citation (ISO format)
SPERA, Marcello et al. Insight into the Charge Density Wave Gap from Contrast Inversion in Topographic STM Images. In: Physical Review Letters, 2020, vol. 125, n° 267603. doi: 10.1103/PhysRevLett.125.267603
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Identifiers
ISSN of the journal0031-9007
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