Different is more - Selected works in heterostructures of transition metal dichalcogenides

Heterostructures are composite materials composed of different parts put together, and they are designed to bring artificial properties. Especially after the discovery of graphene in 2004 and later other two-dimensional layered materials, the idea of assembling heterostructures like toy bricks came true and became a daily routine in quantum material research. These studies continue as many heterostructures are waiting to be realized and direct synthesis and transfer technology are expecting optimization and upgrading. On the other hand, people can now expect to use simple materials and easy protocols to reproduce strongly correlated quantum phenomena shown before in complex compounds with multiple components, such as unconventional high-temperature superconductivity in cuprates, heavy fermions and quantum criticality in rare earth compounds. The simple material platform saves energy for reproducing and reduces the difficulty of analysis. The work here chooses transition metal dichalcogenides with a layered structure as the building blocks. Together with heterostructure technology, they bring new opportunities and new insights to these challenges. This booklet tries to answer the question of what more physics will emerge when assembling different materials together, by presenting several examples, as well as necessary experimental and theoretical tools. It first briefly introduces all necessary tools, e.g., the materials transition metal dichalcogenides, molecular beam epitaxy, scanning tunneling microscopy and spectroscopy tech, as well as theories such as the Hubbard model, the single impurity Anderson model and the Kondo model. Together with these techs in the odyssey of searching new quantum phases, some key findings are reported, e.g., a doped Mott insulator in the vertical heterostructure 1T/1H-NbSe2, where the 1T-phase gives Hubbard model physics and that 1H-phase acts as a charge transfer dopant; 1D interfaces in 2D lateral heterostructures 1T-VSe2—1H-NbSe2, with side-coupled Kondo resonance where VSe2 provides localized magnetic moments and NbSe2 provides conduction electrons; and finally other heterostructure applications. These compositions of different components effectively and seamlessly bring new properties which cannot be found in solo materials. These experiments successfully explore new synthesizing methods and discover new condensed matter platforms for many-body physics. These different materials, different Hamiltonian terms bring more phases and more physics.