Charge density waves in layered materials

Charge density waves (CDW) are periodic modulations of the charge density in low-dimensional metals, which can be also characterized by periodic lattice distortion (PLD) which results in a modulation of atomic positions. Quasi two-dimensional (2D) transition metal dichalcogenides including 1T/2H-TaSe₂, 1T/2H-TaS₂, 2H-NbSe₂, and 1T-TiSe₂ are some of the low dimensional metals that exhibit strong CDW distortions whose transition temperature and commensuration varies mainly with temperature. In dependence of the dimensionality, pressure, intercalation, and doping, the transition temperature can also be affected. Thus, structural studies using electron diffraction, atomically resolved imaging (see Fig. 1), and electron energy-loss spectroscopy of 2D transition metal dichalcogenides that exhibit charge density waves/periodic lattice distortions. This includes 1T/2H-TaSe₂, 1T/2H-TaS₂ and 1T-TiSe₂. 

Moreover, transition-metal dichalcogenides can be intercalated with alkali metals and many organic molecules. This may result in dramatic changes in the atomic and electronic structure as well as transport properties of the host structure. We are conducting systematic intercalation studies of CDW materials with organic molecules and study changes in the electronic and atomic structure.