Exploring the Electronic Properties of Two-dimensional Materials by Quantum Well Resonant Tunneling Diode

Abstract

The rising interest in correlations and topology in van der Waals (vdW) heterostructures calls for the exploration of experimental techniques that can examine the electronic structure of two-dimensional systems. In this thesis, I developed a van der Waals materials-based probing technique, the quantum well resonant tunneling diode (QWRTD), to investigate the electronic information of various low-dimensional systems. First, the density of states (DOS) of mono-layer Mo_S versus energy is characterized by the dI/dV - V measurements, where the local DOS maxima at the high-symmetry points K, Q₁, and Q₂ are clearly observed and confirmed by the theoretical calculations. Second, non-uniform strain-induced pseudo-magnetic fields of approximately 160 T are reported in the FLG nanobubble, which is further validated in devices after removing the bubbles using scanning contact mode atomic force microscopy (AFM). Third, Mott and generalized Wigner crystal states are observed near the conduction band edge (CBE) of a 56^。twisted bilayer MoS₂ (tMoS₂), and these states are examined as possible integer and fractional Chern insulating states. Lastly, in a reversed QWRTD, both linear and non linear Landau level splits are measured above -0.9 V when using FLG to probe the conduction band of a 56^。 tMoS2. These splits could originate from either the high-energy Moire band at the M point in tMoS2 or the displacement field-induced mixed bands in FLG. This thesis demonstrates a comprehensive study of probing the electronic information of low-dimensional systems with vdW materials-based QWRTD, showing its capability of investigating precise electronic structure, strain engineering, correlations and topology