Insight into the charge density wave gap from contrast inversion in topographic STM images

Abstract

Charge density waves (CDWs) are understood in great details 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 ($E_F$) 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 analyse the CDW pattern and modulation amplitude in 1$T$-TiSe${}_2$, we find that CI takes place at an unexpected negative sample bias because the CDW gap opens away from $E_F$, 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.

arXiv commentMain text 8 pages, 4 figures + Supplemental Material 7 pages, 6 figures

References in corpus (13)

• Influence of domain walls in the incommensurate charge density wave state of Cu intercalated 1$T$-TiSe${}_2$
• Orbital- and $k_z$-selective hybridisation of Se 4p and Ti 3d states in the charge density wave phase of TiSe${}_2$
• Critical role of the exchange interaction for the electronic structure and charge-density-wave formation in TiSe2
• Microscopic evidence for strong periodic lattice distortion in 2D charge-density wave systems
• Stripe and short range order in the charge density wave of 1T-Cu${}_x$TiSe${}_2$
• STM microscopy of the CDW in 1T-TiSe2 in the presence of single atom defects
• Strong electron-lattice coupling as the mechanism behind charge density wave transformations in transition-metal dichalcogenides
• Semimetal-to-semiconductor transition and charge-density-wave melting in $1T$-TiSe${}_{2-x}$S${}_x$ single crystals
• Unveiling the Charge Density Wave Inhomogeneity and Pseudogap State in 1T-TiSe2
• Energy-dependent spatial texturing of the charge order in $1T$-Cu${}_x$TiSe${}_2$
• Local resilience of the $1T$-TiSe${}_2$ charge density wave to Ti self-doping
• Visualizing the Charge Density Wave Transition in 2H-NbSe2 in Real Space
• Unveiling the Semimetallic Nature of 1$T$-TiSe${}_2$ by Doping its Charge Density Wave

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• Real-space Observation of Incommensurate Spin Density Wave and Coexisting Charge Density Wave on Cr(001) surface
• Nanoscale visualization and spectral fingerprints of the charge order in ScV6Sn6 distinct from other kagome metals
• Realization of multiple charge density waves in NbTe2 at the monolayer limit
• Semiconductor-metal phase transition and emergent charge density waves in 1T-ZrX${}_2$ (X = Se, Te) at the two-dimensional limit
• Charge Density Wave and Ferromagnetism in Intercalated CrSBr
• Superconductivity induced by gate-driven hydrogen intercalation in the charge-density-wave compound 1T-TiSe2
• Absence of in-gap modes in charge density wave edge dislocations of the Weyl semimetal (TaSe${}_4$)${}_2$I
• Atomically sharp 1D interfaces in 2D lateral heterostructures of VSe${}_2$-NbSe${}_2$ monolayers
• Melting of unidirectional charge density waves across twin domain boundaries in GdTe${}_3$
• Chiral charge density wave and backscattering-immune orbital texture in monolayer 1T-TiTe2
• Peculiarities of electron transport and resistive switching in point contacts on TiSe2, TiSeS and CuxTiSe2
• Doping Tunable CDW Phase Transition in Bulk 1T-ZrSe${}_2$
• Stacking of charge-density waves in 2H-NbSe${}_2$ bilayers
• Competing electronic states emerging on polar surfaces
• Feedback loop dependent charge density wave imaging by scanning tunneling spectroscopy
• Coexistence of stripe order and superconductivity in NaAlSi
• Multiband charge density wave exposed in a transition metal dichalcogenide
• Moiré-resonant surface state in ultrathin RuO${}_2$