An Investigation of Electronic Phases and Charge Dynamics in Low-Dimensional System

Abstract

In condensed matter physics, the concepts of topology and symmetry are of paramount importance, particularly in understanding quantum phase transitions. Topology classifies objects based on their topological properties, which are properties that are preserved under continuous deformation. This is relevant to a wide range of phenomena, such as topological insulators and the quantum Hall effect. On the other hand, symmetry is used to understand phase transitions, where a higher symmetry group is broken into a lower symmetry subgroup. The study of quantum phases and phase transitions is a fundamental theme in condensed matter physics, and topology and symmetry play a critical role in comprehending these phenomena. This field of research is vital in understanding the behavior of matter at the quantum level and has potential applications in quantum computing and other technologies This thesis mainly explored the quantum phase transitions through resistance fluctuation spectroscopy. The first part of the thesis focused on uncovering the electronic phases in 1T-TaS2 . The presence of a low temperature insulating phase in 1T-TaS2 has been a matter of debate among researchers, with recent theoretical calculations suggesting that it is a result of out-of-plane stacking rather than a Mott insulator Our findings suggest that out-of-plane stacking might be responsible for the observed insulating phase at low temperatures. Our study showed that the device exhibited metallic behavior at low temperatures, but an insulating phase was restored over a narrow range as the temperature increased. The system also exhibited signs of electrical phase separation prior to the restoration of the insulating phase, as seen through quantized jumps in conductance between two well-defined levels. These jumps were speculated to result from metallic domain walls separating insulating regions. In the second part of the thesis, we studied the resistance fluctuations near the Lifshitz transition in WTe2 using electrical and thermal transport studies. The presence of two holes and two electron pockets in the band structure at low temperatures and the disappearance of the hole pockets above the transition temperature could be related to a topological phase transition in the material. An electrical noise peak was observed at the transition temperature, which was attributed to inter-band scattering at Weyl points. The study emphasized the importance of high-quality samples for detecting the unique properties of Weyl semi-metals. In the final section of the thesis, the behavior of charge dynamics in a quasi-two-dimensional electron gas (q2DEG) at the LaScO3/SrTiO3 interface was studied through resistance fluctuation spectroscopy. Despite persistent efforts, the source of charge carriers at the oxide interface remains elusive. [7, 8, 9]. Our study indicated that the role of oxygen vacancies in transport properties at the oxide interface requires further exploration. The q2DEG at the LaScO3/SrTiO3 interface was found to exhibit random telegraphic noise (RTN) at high temperatures, which disappeared below 40 K, indicating a temperature-dependent behavior of the charge dynamics. Based on these observations, we posit that the RTN is likely the result of charge exchange between mid-gap defect states in the bulk and the q2DEG.