Date of Award

Summer 8-15-2021

Author's School

Graduate School of Arts and Sciences

Author's Department

Physics

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

The field of two-dimensional(2D) materials is experiencing rapid growth and attracting tremendous research interests within the condensed matter community due to its ultimate thickness dimension and unique physical properties. The consistently emerging novel 2D materials not only provide extraordinary intrinsic properties of their single layer and multi- layer structures but also exhibit fascinating responses to the tunable external conditions. The fertile contents and boundless possibilities of novel 2D materials make it one of the pivots of modern nanotechnology towards deepening the physics understanding and promising practical applications.

In the first part of the thesis, we reveal the distinct Stark effects of few layers transition metal dichalcogenides (TMDs) under different doping and external field conditions through first-principal calculation and explain the findings with the layer wavefunction based tight-binding model. Then the tunable electric and optical properties of multi-layer black phosphorus (BP) under external displacement field is further discussed with the effective Hamiltonian based on the tight-binding model and \vec{k}\cdot\vec{p} theory. Meanwhile, we study the interlayer exciton properties of bilayer MoSe2/WSe2 heterostructure with a small twisting angle between layers and reveal the corresponding exciton moiré potential.

The second part of this thesis focuses on the magnetic properties of novel 2D materials such as chromium trihalides (CrX3). An anisotropy Heisenberg model based on first-principal parameters along with Monte Carlo (MC) simulations is carried out to study the fundamental Curie temperature (Tc) of 2D magnets easy-axis and topological defects of easy-plane 2D magnets. Particularly, we find a universal, linear dependence between Tc and magnetic interactions within the parameter space of realistic materials. Meanwhile, we propose that weak spin-orbit coupling (SOC) material, monolayer chromium trichloride (CrCl3), can be a promising candidate for observing the vortex/anti-vortex type of topological defects so-called merons, at finite temperature. Finally, we present a further quantitative model study of such non-collinear spin texture and their interactions within 2D magnets.

Language

English (en)

Chair and Committee

Li Yang

Committee Members

Erik A. Henriksen, Kenneth F. Kelton, Rohan Mishra, Sheng Ran,

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