Date of Award
Doctor of Philosophy (PhD)
Physics and Astronomy
Dr. Jian He, Committee Chair
Dr. Feng Ding
Dr. Donald Liebenberg
Dr. Terry M. Tritt
Charge density wave (CDW) is a many-body state of matter in which both lattice and electron density are modulated by a new periodicity. CDW features discrete translational symmetry breaking, and mostly occurs in low-dimensional materials. Although CDW behaviors have been found in many materials, the underlying mechanism and the driving forces of CDW transition are still unclear. In particular, the origin of CDW in two-dimensional materials, especially in layered transition metal dicalchogenides (TMDCs), may be distinct from that in one-dimensional materials.
In this dissertation, the CDW transition in VSe2, a layered TMDC material, is explored. Density functional theory (DFT) calculations were performed on bulk VSe2, and the calculated results of spin-polarized band structure, density of states (DOS) and Fermi surface, along with phonon dispersion relation and phonon DOS are presented. Experimentally, both single- and polycrystalline VSe2 samples were investigated by means of electrical resistivity, Seebeck coefficient, Hall coefficient/Hall angle, magnetic susceptibility, heat capacity and thermal conductivity measurements. The anomalies of these physical properties across CDW transition temperature are studied and discussed. The experimental results indicate that the CDW in VSe2 is weak, and only a small portion of Fermi surface is gapped during the transition. The comparison with three other CDW materials sheds light on the different origins of CDW formation in TMDCs.
Additionally, anomalies are found at very low temperatures in the heat capacity and electrical resistivity measurements of both single- and poly-crystalline VSe2. The anomaly in heat capacity is presumably due to Schottky heat capacity caused by the nuclear spin of V atoms.
Zhou, Menghan, "Vanadium Diselenide: On the Verge of Charge Density Wave" (2016). All Dissertations. 2414.