Characterization of collective ground states in single-layer NbSe sub(2)

• Published in: Nature physics 2016-01, Vol.12 (1), p.92-97
• Main Authors: Ugeda, Miguel M, Bradley, Aaron J, Zhang, Yi, Onishi, Seita, Chen, Yi, Ruan, Wei, Ojeda-Aristizabal, Claudia, Ryu, Hyejin, Edmonds, Mark T, Tsai, Hsin-Zon, Riss, Alexander, Mo, Sung-Kwan, Lee, Dunghai, Zettl, Alex, Hussain, Zahid, Shen, Zhi-Xun, Crommie, Michael F
• Format: Article
• Language: English
• Subjects: Correlation; Electronics; Fermi surfaces; Formations; Ground state; Scanning tunneling microscopy; Superconductivity; Two dimensional
• ISSN: 1745-2473
• DOI: 10.1038/nphys3527

Layered transition metal dichalcogenides are ideal systems for exploring the effects of dimensionality on correlated electronic phases such as charge density wave (CDW) order and superconductivity. In bulk NbSe sub(2) a CDW sets in at T sub(CDW) = 33K and superconductivity sets in at T sub(c) = 7.2K. Below T sub(c) these electronic states coexist but their microscopic formation mechanisms remain controversial. Here we present an electronic characterization study of a single two-dimensional (2D) layer of NbSe sub(2) by means of low-temperature scanning tunnelling microscopy/spectroscopy (STM/STS), angle-resolved photoemission spectroscopy (ARPES), and electrical transport measurements. We demonstrate that 3 3 CDW order in NbSe sub(2) remains intact in two dimensions. Superconductivity also still remains in the 2D limit, but its onset temperature is depressed to 1.9K. Our STS measurements at 5K reveal a CDW gap of Delta = 4meV at the Fermi energy, which is accessible by means of STS owing to the removal of bands crossing the Fermi level for a single layer. Our observations are consistent with the simplified (compared to bulk) electronic structure of single-layer NbSe sub(2), thus providing insight into CDW formation and superconductivity in this model strongly correlated system.