Exploring carrier dynamics in van der Waals heterostructures with shot noise spectroscopy thermoelectricity and opto electronic study

Abstract

In the last two decades, there has been tremendous progress in two-dimensional (2D) - material research. It is mainly due to the availability of a large selection of 2D-materials and their van-der-Waals heterostructures. The 2D-material based heterostructures, in particular, have significant fundamental and technological importance due to their tunable electrical and optical properties. In this thesis, we have studied three types of 2D-heterostructures: graphene pn junction, magic-angle twisted bilayer graphene, and MoTe2-MoS2 based hetero-pn junction. We investigate the carrier transport and its dynamics using cutting-edge probes like shot noise spectroscopy, thermoelectricity, and optoelectronic studies. In the first part of the thesis, we will present our research on equilibration dynamics of quantum Hall (QH) edge states in graphene pn junction (PNJ). Graphene pn junction with co-propagating spin-valley polarized QH edges is a promising platform for studying electron interferometry. Though several conductance measurements have been attempted for such PNJs, the edge dynamics of the spin-valley symmetry broken edge states remain unexplored. In this study, we present the measurements of conductance together with shot noise, an ideal tool to unravel the dynamics, in dual graphite gated hexagonal boron nitride encapsulated high mobility graphene devices. The conductance data show that the symmetry broken QH edges at the PNJ follow spin selective equilibration. The shot noise results as a function of both p and n side filling factors reveal the unique dependence of the scattering mechanism. Remarkably, the scattering is found to be fully tunable from incoherent to a coherent regime with the increasing number of QH edges at the PNJ, shedding crucial insights into the velocity-dependent phase coherence of the QH edges at a pn junction. Furthermore, we study the bias-dependent tunneling between the and#957; = ±1 QH edges of the pn junction. At zero bias, we observe finite tunneling (t and#8764; 0.5), which remains almost constant...