Robust Behavior of Charge Density Wave Quantum Motif Star‐of‐David in 2D NbSe₂ Nanocrystals

Abstract

Charge density wave (CDW) is a typical collective phenomenon, and the phase change is generally accompanied by electronic transition with potential device applications. For the continuous miniaturization of devices, it is important to investigate the size effect down to the nanoscale. In this work, single‐layer (SL) 1T‐NbSe2 islands provide an ideal research platform to investigate the size effect on CDW arrangement and electronic states. The CDW motifs (Star‐of‐David [SOD]) at the island border are along the edge, and those at the interior tend to arrange in a triangular lattice for islands as small as 5 nm. Interestingly, in some small islands, the SOD clusters rearrange into a square‐like lattice, and each SOD cluster remains robust as a quantum motif, both in the sense of geometry and electronic structures. Moreover, the electronic structure at the center of the small islands is downwards shifted compared to the big islands, explained by the spatial extension of the band bending originating from the edge of the islands. These findings reveal the robust behavior of CDW motifs down to the nanoscale and provide new insights into the size‐limiting effect on 2D2D CDW ordering and electronic states down to a few nanometer extremes.

Two-dimensional materials for future information technology: status and prospects

“…The small 1T-NbSe2 has five SOD clusters in the interior, with both chiralities, forming a square-like pattern. However, the shape and electronic states of each SOD are largely preserved from the atomic imaging and the dI/dV spectroscopy compared to the normal triangular packing, showing a robust behavior with SOD as the motif [230].…”

“…(h)-(i) Nanoisland of 1T-NbSe2, forming a quantum dot. On the island, the SOD triangular array may rearrange by a square-like pattern, but the shape and electronic states of each SOD are largely preserved, showing a robust behavior [230]. (j) 1D trench defect induced by thermal annealing of VSe2 [216].…”

Fundamental Limits of Few-Layer NbSe2 Microbolometers at Terahertz Frequencies

“…Layered van der Waals (vdW) superconductors have recently emerged as a convenient platform for investigating quantum phenomena arising in two dimensions and for future technology prototypes. − Among them, two-dimensional (2D) niobium diselenide (NbSe 2 ) is one of the most extensively studied compounds. − Not only has it enabled the observation of numerous spectacular effects ranging from high-critical-field Ising superconductivity and charged density waves − to unusual continuous paramagnetic-limited superconducting phase transitions and magnetochiral anisotropy, , but it has also given rise to several interesting applications such as superconducting diodes and rectennas . Despite significant progress in understanding the fundamental properties of this material via transport and optical experiments, − little is known about the response of NbSe 2 to terahertz (THz) radiation. − …”