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

• Published in: Nature communications Vol. 8; no. 1; pp. 1 - 6
• Main Authors: Chen, P., Pai, Woei Wu, Chan, Y.-H., Takayama, A., Xu, C.-Z., Karn, A., Hasegawa, S., Chou, M. Y., Mo, S.-K., Fedorov, A.-V., Chiang, T.-C.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 11.09.2017; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/119/2795; 639/766/119/544; 639/766/119/995; Bulk density; Charge density waves; Density; Electronic properties and materials; Emergence; Fermi level; Humanities and Social Sciences; MATERIALS SCIENCE; Microscopy; multidisciplinary; Nanotechnology devices; Phase transitions and critical phenomena; Photoelectric emission; Photoelectron spectroscopy; Physical properties; Quantum confinement; Scanning tunneling microscopy; Science; Science (multidisciplinary); Spectroscopy; Spectrum analysis; Surfaces, interfaces and thin films; Transition temperature
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-017-00641-1

Two-dimensional materials constitute a promising platform for developing nanoscale devices and systems. Their physical properties can be very different from those of the corresponding three-dimensional materials because of extreme quantum confinement and dimensional reduction. Here we report a study of TiTe 2 from the single-layer to the bulk limit. Using angle-resolved photoemission spectroscopy and scanning tunneling microscopy and spectroscopy, we observed the emergence of a (2 × 2) charge density wave order in single-layer TiTe 2 with a transition temperature of 92 ± 3 K. Also observed was a pseudogap of about 28 meV at the Fermi level at 4.2 K. Surprisingly, no charge density wave transitions were observed in two-layer and multi-layer TiTe 2 , despite the quasi-two-dimensional nature of the material in the bulk. The unique charge density wave phenomenon in the single layer raises intriguing questions that challenge the prevailing thinking about the mechanisms of charge density wave formation. Due to reduced dimensionality, the properties of 2D materials are often different from their 3D counterparts. Here, the authors identify the emergence of a unique charge density wave (CDW) order in monolayer TiTe 2 that challenges the current understanding of CDW formation.