Emergence of charge density waves and a pseudogap in single-layer TiTe2

Chen, P.; Pai, Woei Wu; Chan, Yang-Hao; Takayama, A.; Xu, Caizhi; Karn, Abhishek; Hasegawa, Shuji; Chou, M. Y.; Mo, S.-K.; Fedorov, A. V.; Chiang, T.‐C.

doi:10.1038/s41467-017-00641-1

Cited by 106 publications

(186 citation statements)

References 28 publications

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“…The surface structure probed by atomic resolution STM at RT and their corresponding fast Fourier transform (FFT) patterns are presented in Figure . The 1 ML TiTe 2 STM image and 2 × 2 FFT (Figure a,b) are very similar to data previously reported for relaxed 1 ML TiTe 2 at 4.2 K and attributed to CDW superstructure . The main difference is that in the present work the Moiré pattern attributed to the interaction with the InAs substrate is also visible.…”

Section: Resultssupporting

confidence: 90%

“…The electronic band structure of 1 ML ( Figure a) and 50 ML TiTe 2 (Figure b) are imaged by in situ ARPES. They reveal a semimetalic material with two Te 5p valence bands crossing E F near Γ, which overlap with Ti 3d conduction bands at M(L) by 0.2–0.3 eV, as expected from DFT calculations and experimental data of undistorted 1T TiTe 2 , suggesting that the PLD/CDW formation in our epitaxial films does not have a large influence on the electronic band structure. In contrast to common wisdom that a CDW should open a gap at the Fermi level ( E f ), no such gap is observed here.…”

Section: Resultssupporting

confidence: 78%

“…The stability of 1 ML and bulk 1T TiTe 2 structure is studied by density functional theory (DFT) and results on phonon dispersion are presented in Figure a and Figure S2 (Supporting Information). Employing Perdew–Burke–Ernzerhof (PBE) functionals, the 1 ML 1T structure is predicted to remain stable since only a small phonon softening at M occurs (Figure S2, Supporting Information) similar to previous report . However, if Heyd–Scuseria–Ernzerhof (HSE) hybrid functionals are used (see the Experimental Section) a large Kohn anomaly is predicted in one of the acoustic branches near M (Figure a), implying a large 1T structural instability which could induce a transition to a lattice with lower symmetry.…”

Section: Resultssupporting

confidence: 73%

“…This is compatible with observations in other CDW cases. For example, in the case of 1 ML CDW TiTe 2 valence and conduction bands overlap at E f , while in CDW TiSe 2 , E f is not located in the gap but it is lying within one of the bands having finite density of states. It is worth noticing that the multilayer TiTe 2 (Figure b) with a stronger CDW structure compared to 1 ML as evidenced from Figure , shows a lowering of one of the bands near Γ, about 0.25 eV below E f (blue marks in Figure b).…”

Section: Resultsmentioning

confidence: 99%

“…The most recent experimental and theoretical works focus on the large area growth of the CDW phase the thickness dependence, and the possible unconventional behavior in the ultimate 2D limit of a single layer TiSe 2 . On the other hand, the other Ti dichalcogenides namely TiS 2 and TiTe 2 did not show any clear evidence until very recently when a CDW state was reported only for 1 monolayer (ML)‐thin TiTe 2 at temperatures lower than 92 K . It is surprising that the CDW in TiTe 2 was found to be totally suppressed for films thicker than 1 ML, unlike the case of other TMDs where 1 ML and bulk‐like films both make the transition to a CDW at nearly the same temperature.…”

Section: Introductionmentioning

confidence: 99%

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Room Temperature Commensurate Charge Density Wave in Epitaxial Strained TiTe₂ Multilayer Films

Fragkos

Sant

Alvarez

et al. 2019

Adv Materials Inter

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Despite a large number of studies [2,3] over the years since the first discovery [7] and a couple of comprehensive reviews [8,9] the actual mechanism for PLD/CDW formation is still under debate. The most recent experimental [10][11][12][13] and theoretical [14] works focus on the large area growth of the CDW phase [13] the thickness dependence, and the possible unconventional behavior in the ultimate 2D limit of a single layer TiSe 2 . [10][11][12]14] On the other hand, the other Ti dichalcogenides namely TiS 2 and TiTe 2 did not show any clear evidence until very recently when a CDW state was reported only for 1 monolayer (ML)-thin TiTe 2 at temperatures lower than 92 K. [15] It is surprising that the CDW in TiTe 2 was found to be totally suppressed for films thicker than 1 ML, [15] unlike the case of other TMDs where 1 ML and bulk-like films both make the transition to a CDW at nearly the same temperature.The interest about TiTe 2 is continuously increasing in view of theoretical predictions [16] and more recent experimental evidence [17] about pressure induced topological phase transitions in TiTe 2 . The possibility to also manipulate superconductivity by external pressure as predicted [18] and more recently evidenced [19] in bulk TiTe 2 creates the prospect to explore the emergence of topological superconductivity in this material. In the latter work [19] it has been shown that under nonhydrostatic pressure, a CDW-like state with estimated transition temperature above room temperature (RT) appears in bulk TiTe 2 at around 0.5-1.8 GPa. These results call for a re-examination of the possibility to obtain a CDW in multilayer TiTe 2 and indeed at RT with good potential for real world applications utilizing the properties of the CDW state. These applications include a voltage-controlled oscillator device operating at room temperature, [20] fast electronic resistance switching for nonvolatile memories, [21,22] and field-effect transistor devices potentially suitable for implementation of non-Boolean logic. [23] In this paper it is shown that multilayer films (50 ML ≈ 32 nm), as well as single layer TiTe 2 epitaxially grown on InAs(111)/ Si(111) substrates by molecular beam epitaxy exhibit, in ambient pressure conditions, a CDW distortion at room temperature which is sustained up to higher temperatures, at least 400 °C, as evidenced by reflection high energy electron diffraction (RHEED) ( Figure S1, Supporting Information). The results are explained in terms of anisotropic strain imposed by the substrate.The group IVB 2D transition metal dichalcogenides are considered to be stable in the high symmetry trigonal octahedral structure due to the lack of unpaired d-electrons on the metal site. It is found that multilayer epitaxial TiTe 2 is an exception adopting a commensurate 2 × 2 × 2 charge density wave (CDW) structure at room temperature with an ABA type of stacking as evidenced by direct lattice imaging and reciprocal space mapping. The CDW is stabilized by highly anisotropic strain imposed by the substrate with an...

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Section: Resultssupporting

confidence: 90%

Section: Resultssupporting

confidence: 78%

Section: Resultssupporting

confidence: 73%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Room Temperature Commensurate Charge Density Wave in Epitaxial Strained TiTe₂ Multilayer Films

Fragkos

Sant

Alvarez

et al. 2019

Adv Materials Inter

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2D Group IVB Transition Metal Dichalcogenides

Yan

Gong

Wangyang

et al. 2018

Adv Funct Materials

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Semiconductor technology is currently impaired by the surface dangling bond of materials, which introduces scattering and interface traps. 2D materials, especially transition metal dichalcogenides (TMDs) with different main groups, have settled this issue by utilizing unique atomically smooth surfaces and van der Waals (vdW) structures. Over the past few decades, many processes for exploring new materials, manipulating physical properties, and synthesizing single crystals have been developed. Among these 2D materials, group IVB TMDs are distinguished for their splendid physical properties, including ultrahigh mobility, charge density wave, superconducting transitions, etc. Here, the recent advances in group IVB TMDs are reviewed, which offer easy access to next generation nano-, opto-, thermal-electronic, energy storage and conversion applications. Both the advantages and challenges of these studies are summarized to further clarify existing problems.such as ZrSe 2 is up to 8000 µA µm −1 , which is 10 3 times higher than that of MoS 2 . [11] Group IVB TMDs are also promising thermoelectric materials for their enhanced thermoelectric performance with a high power factor such as TiS 2 . [12][13][14][15][16] These features indicate the great potential of group IVB TMDs for adoption into electronics. In addition, group IVB TMDs show fascinating electrochemical performances as hold materials [17][18][19] or electrodes [20,21] in catalysis [22,23] and batteries [24,25] (Figure 1). A breakthrough may be introduced in nanoelectronic and energy fields for ultrahigh performances and nontoxicity of 2D group IVB TMDs.In this review, we focus on the electronic structures of 1T-phase group IVB TMDs, the abundant properties of group IVB TMDs, and their applications in electronic devices. In particular, we start with the unique crystal structures and calculated electronic structures of 2D group IVB dichalcogenides. Then, the great properties and the current studies in electronic devices are reviewed with an emphasis on recently reported transistor and photodetectors based on group IVB TMD nanosheets. In the third part, the synthesis of group IVBs nanostructures is described. We review the current approaches for the isolation of ultrathin sheets and analyze the advantages and drawbacks of various preparation methods. At last, we present the challenges and future prospects of group IVB TMDs. Crystal and Electronic StructuresThe electronic structures of 2D TMDs strongly depend on their crystal structures and d-electron counts. Another crucial feature is the partially filled d bands of transition metals. Bulk TMDs are composed of ordered stacking monolayers connected by the weak van der Waals (vdW) interaction. This kind of layered material exists multifarious in polymorphs and commonly crystallize into three different structures in 1T, 2H, and 3R phases. For group IVB TMDs, 1T phase is more stable than 2H phase in reversal of group VIB TMDs due to their lower formation energies. [23] Figure 2a,b depicts the two typical structures o...

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2D Metallic Transition‐Metal Dichalcogenides: Structures, Synthesis, Properties, and Applications

Zhao

Shen

Zhang

et al. 2021

Adv Funct Materials

182

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2D materials and the associated heterostructures define an ideal material platform for investigating physical and chemical properties, and exhibiting new functional applications in (opto)electronic devices, electrocatalysis, and energy storage. 2D transition metal dichalcogenides (2D TMDs), as a member of the 2D materials family including 2D semiconducting TMDs (s-TMDs) and 2D metallic/semimetallic TMDs (m-TMDs) have attracted considerable attention in the scientific community. Over the past decade, the 2D s-TMDs have been extensively researched and reviewed elsewhere. Because of their distinctive physical properties including intrinsic magnetism, chargedensity-wave order and superconductivity, and potential applications, such as high-performance electronic devices, catalysis, and as metal electrode contacts, 2D m-TMDs have grabbed widespread attention in recent years. However, reviews demonstrating the m-TMDs systematically and comprehensively have been rarely reported. Here, the recent advances in 2D m-TMDs in the aspects of their unique structures, synthetic approaches, distinctive physical properties, and functional applications are highlighted. Finally, the current challenges and perspectives are discussed.

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Emergence of charge density waves and a pseudogap in single-layer TiTe2

Cited by 106 publications

References 28 publications

Room Temperature Commensurate Charge Density Wave in Epitaxial Strained TiTe₂ Multilayer Films

Room Temperature Commensurate Charge Density Wave in Epitaxial Strained TiTe₂ Multilayer Films

2D Group IVB Transition Metal Dichalcogenides

2D Metallic Transition‐Metal Dichalcogenides: Structures, Synthesis, Properties, and Applications

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Emergence of charge density waves and a pseudogap in single-layer TiTe2

Cited by 106 publications

References 28 publications

Room Temperature Commensurate Charge Density Wave in Epitaxial Strained TiTe2 Multilayer Films

Room Temperature Commensurate Charge Density Wave in Epitaxial Strained TiTe2 Multilayer Films

2D Group IVB Transition Metal Dichalcogenides

2D Metallic Transition‐Metal Dichalcogenides: Structures, Synthesis, Properties, and Applications

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Room Temperature Commensurate Charge Density Wave in Epitaxial Strained TiTe₂ Multilayer Films

Room Temperature Commensurate Charge Density Wave in Epitaxial Strained TiTe₂ Multilayer Films