On the energy dissipation of charge density wave systems and topological insulator surfaces

Dissipation mechanisms in a broad spectrum of physical systems and media attracted great interest among fundamental scientific and applied communities. Understanding the origin of various energy dissipation (non-contact friction) mechanism is still a wide-open problem. The frictional nature of layered systems, such as those hosting charge density wave (CDW) and topologically protected surface state, awaits to be investigated. Regarding CDW, I investigated non-contact energy dissipation on 1T-TaS2 surface. I studied the origin of dissipation on two phases of CDW and the effect of Mott insulating state on dissipated power. The low-temperature experimental results indicate that on a strongly pinned commensurate CDW phase, Joule dissipation is the main dissipation mechanism. The character of dissipation changes at room temperature and for nearly commensurate CDW phase. There the fluctuation driven dissipation is the main dissipation channel. The room temperature spectroscopy performed on the nearly commensurate phase of charge density wave indicates that the source of the fluctuating force and dissipation is the stochastic motion of weakly pinned charge density waves. Next, I studied the electronic nature of Bi2Te3 surface and energy dissipation on this topologically protected surface. I observed the suppression of the common Joule type losses due to a topologically protected surface state, which prevents electron scattering into the bulk states. It was found that dissipated power is related to the presence of image potential states that are found in the gap between the tip and the sample. The study shows that the damping coefficient increases due to charge fluctuation in the system when image potential states get populated via a single or few-electron tunneling process. Furthermore, the application of magnetic fields leads to the breaking of the topologically protected surface state and the rise of the Joule dissipation. Last, I report on the observation of dissipation peaks at selected voltage-dependent tip-surface distances on the oxygen-deficient strontium titanate (SrTiO3) surface. The experiment was performed at low temperatures (T=5K). The observed dissipation peaks are attributed to tip-induced charge state transitions in quantum-dot-like entities formed by a 2D system of single oxygen vacancies present at the SrTiO3 surface.