Exploring Novel Quantum States and Manipulating Different Quantum Degrees of Freedom in Two-Dimensional Crystals, Heterostructures and Nano-Metamaterials

Condensed Matter Seminars

Speaker: Nai-Chang Yeh, Department of Physics and Kavli Nanoscience Institute California Institute of Technology
Date & Time: Thu, 2018-02-15 14:00 - 15:00
Location: AMPEL 311
Local Contact:
Intended Audience:

Recent advances in nanofabrication technology and in the development of two-dimensional (2D) crystals and heterostructures/interfaces of novel materials have enabled new possibilities to explore novel quantum states and manipulate different quantum degrees of freedom (e.g., spin, valley, symmetry, topology, etc.) in materials. For instance, 2D crystals of van der Waals (vdW) materials with honeycomb lattice structures, such as semi-metallic graphene, insulating hexagonal boron nitride (h-BN), and semiconducting transition metal dichalcogenides (TMDCs) that exhibit strong spin-valley coupling, have simulated intense research efforts due to their rich physical properties and great promises for technological applications in nanoelectronics, spintronics, valleytronics and optoelectronics. The surface and edge states of strong spin-orbit coupled topological insulators in proximity to either ferromagnetism or superconductivity can manifest the elusive topological magnetoelectric effect (TME) or Majorana fermionmodes, which are not only of fundamental scientific importance but also promising for applications to spin-orbitronics and quantum information technology. Monolayer interfaces of iron-based superconductors (e.g., FeSe with a bulk superconducting transition temperature T_c ~ 8 K) with polar substrates (such as SrTiO₃ or TiO₂) have found an enhancement in the T_c value by nearly ten times, suggesting the importance of quantum confinement and strong-coupling for the occurrence of high-T_c superconductivity. Nanoscale strain engineering of graphene by nanofabrication of meta-structures can induce giant pseudo-magnetic fields (up to ~ 10⁴ Tesla local fields at nanoscales!) and strong valley polarization for novel valleytronic and optoelectronic devices. In this talk, I will first give an overview of some research highlights in the aforementioned materials frontier, and then describe our ongoing research efforts along these directions. Finally, I’ll discuss various promising applications based on these new trends of approaches.