Investigating and manipulating electronic transport properties of intercalated transition metal dichalcogenides

Abstract

This thesis explores the electronic transport properties of devices based on two-dimensional transition metal dichalcogenides. By developing and optimising fabrication techniques, effective strategies were established for measuring these layered-structure devices, laying the groundwork for examining their unique electronic properties. This work focuses on how changes in external conditions, such as temperature, magnetic field, and electrostatic environment, alter the electronic transport behaviour of the materials and what these changes reveal about the observed phenomena. The main results are detailed in two chapters, each dedicated to a different structure. The first experimental chapter explores the concurrence of Kondo behaviour and magnetic ordering in the intercalated transition metal dichalcogenide AgCrSe₂. Transport measurements across varying temperatures and magnetic fields revealed an unusual upturn in the low-temperature resistivity behaviour, suggesting the single-ion Kondo effect as its origin. By applying Schlottmann’s theoretical framework, it was found that the Kondo temperature and the Néel temperature coincide, indicating a unique correlation. This leads to a new understanding of how magnetic ordering can enable Kondo hybridisation, contrary to the conventional view that magnetic order competes with Kondo scattering. These insights underscore the significance of studying such layered structures, where ionically conductive sheets are intercalated within transition metal planes making exceptional platforms for examining correlated effects and unconventional electronic and magnetic phenomena. The second experimental chapter focuses on the alternately stacked transition metal dichalcogenide 4HbTaS₂. Electrical transport measurements, such as the angular dependence of the upper critical field and the behaviour of the critical current, revealed the 2D nature of superconductivity in this material. Furthermore, ionic liquid gating measurements unveiled a switching effect between resistivity states and suppressed superconductivity under gating. These findings highlight the potential of layered heterostructures to exhibit unique and unconventional electronic transport properties arising from the electronic properties of constituent layers.

Date of Award	2 Dec 2025
Original language	English
Awarding Institution	University of St Andrews Max Planck Institute for Chemical Physics of Solids
Supervisor	Haijing Zhang (Supervisor), Andrew Mackenzie (Supervisor) & Andreas Rost (Supervisor)