Searching for materials with novel electronic behaviours has become essential as conventional semiconductor technologies approach their physical and functional limits. Quantum phases of matter, including charge density waves (CDWs), superconductivity, and topological surface states, offer unique properties that could redefine future electronic and quantum devices. CDWs provide a promising platform for logical circuits, ultra-fast memristive devices, and artificial neuronal networks. Topological materials may enable quantum computing through ultra-stable Majorana zero modes and spintronics via strong spin–momentum locking. However, integrating these phases into functional systems remains challenging, largely due to limited understanding of the mechanisms that govern them.
This thesis establishes a framework for studying the tunability and nature of quantum phases in van der Waals materials under controlled layer and doping conditions. We employ scanning tunnelling microscopy (STM) to investigate how electronic properties evolve with doping in layered transition metal dichalcogenides (TMDs). Exfoliated single crystals are used to ensure high crystalline quality and preserve intrinsic properties. Unlike thin-film techniques such as chemical vapour deposition or molecular beam epitaxy, exfoliation avoids issues of strain, charge transfer, nonstoichiometry, and high defect densities, though flake size remains limited. To overcome this, we developed an STM-compatible framework for preparing highly doped, large-area, few-layer flakes through anodic bonding and space charge doping. This approach enables atomically resolved insight into complex electronic phases in tunable low-dimensional systems.
As a benchmark, we studied molybdenum disulfide, demonstrating successful preparation and identification of monolayer and bilayer flakes via optical contrast and Raman spectroscopy. In zirconium diselenide, we identified a doping-tunable CDW phase and showed that shifting the conduction band enhances or suppresses this order. These findings provide direct evidence linking band structure modifications to CDW emergence. In bulk nickel ditelluride, we present the first comprehensive real-space mapping of multiple topological surface states and Dirac cones using STM. The observed scattering patterns are consistent with spin-split surface bands, and we propose that intercalated nickel atoms locally break time-reversal symmetry, giving rise to spin-flip scattering.
Together, these results establish a versatile framework for probing electronic phase transitions in low-dimensional materials. By combining anodic bonding with space charge doping, we provide a non-invasive route to tune quantum phases and access dimensional crossover regimes, paving the way for device-relevant studies of correlated and topological systems.
