Instructors: Philip Kim,
Harvard University; Jigang Wang,
Iowa State University of Science and Technology; Liqin Ke,
Quantum Materials is a concept that has broadened significantly in recent years, spanning beyond strongly correlated electron materials. In two-dimensional (2D) systems, several classes of quantum materials have been identified beyond graphene, such as transition-metal dichalcogenides, van der Waals crystals and topological insulators. 2D materials are being widely investigated for their appealing properties such as high flexibility, optical transparency or enormous carrier mobility, superior catalytic properties and robust ferromagnetism when sliced to the monolayer limit. Because the electrons in these materials are exposed to interlayer coupling, the properties of these materials are defined not only by the constituent monolayers, but also by the interactions between the layers.
Many fascinating electrical, optical and magnetic properties have recently been reported in quantum materials owing to their reduced dimensionality (strong quantum confinement) and enhanced Coulomb interactions. These materials offer the great opportunity to tune their electronic and magnetic states, structure and interlayer coupling through external stimuli such as photons, electric and magnetic fields and pressure. To broaden the current knowledge on quantum materials, it is necessary to develop operando techniques to quantify, manipulate and measure their properties over a wide range of temporal and spatial scales and under external perturbations. This tutorial will review the recent developments in the rapidly progressing field in exploring the physical properties of quantum materials through a combination of sensitive, ultrafast experimental and computational approaches, and will immensely benefit scientists at all levels.
Topological Quantum Materials for Quantum Electronic Devices
Philip Kim, Harvard University
Modern electronics has heavily relied on the technology to confine electrons in the interface layers of materials. The unique properties of these low dimensional systems are generally understood by considering enhanced quantum effects and increased correlations due to the reduction of available phase space. Quantum effect in low dimensional materials also provides topological states of matter where entangled quantum states can be transformed smoothly with protected symmetries, resulting in robust invariants. In this presentation, we will discuss some of the key physical phenomena such as the Berry phase, quantum Hall and the quantum spin Hall effect. Topology and collective phenomena give quantum materials emergent functions that provide a platform for developing next-generation quantum devices with novel functionality, such as electronics without power dissipation and fault-tolerant quantum computing. We will discuss the prospect of quantum technology based on topological quantum materials.
2:30 pm BREAK
Terahertz Light Control and Nano-Imaging of Quantum Materials
Jigang Wang, Iowa State University of Science and Technology
The recent development of ultrafast THz spectroscopy and nano-imaging tools facilitates discovering and understanding collective excitations and emergent phenomena in quantum materials. In this tutorial, I will discuss strategic advantages, with recent examples, of applying single- and few-cycle THz pulses to probe and control several systems of current focus, including unconventional superconductors, topological matter and perovskite photovoltaic semiconductors. Particularly, THz light-driven coherence and dynamic symmetry breaking allows the observation of quantum beats forbidden by equilibrium symmetry and quantum phases hidden by conventional tuning methods. Finally, I will discuss far-reaching consequences of THz spectroscopy tools at the space-time limit on quantum matter discovery and dynamic control.
Magnetism in Quantum Materials—Computation Approach
Liqin Ke, Ames Laboratory
The magnetic 2D van der Waals materials have received great attention due to their potential applications in spintronics. In this tutorial, I will give an introduction to computational magnetism. In particular, I will focus on the ab initio methods that are used to compute and resolve intrinsic magnetic properties, such as exchange coupling, magnetocrystalline anisotropy and magnetic susceptibility. We will discuss the underlining magnetic mechanisms that may guide the band structure engineering to improve the magnetic properties in these systems.