Integrated Calendar

Topological insulators (TIs) are novel materials that do not conduct elec-tricity in their bulk but possess exceptional conducting electronic states on their surface. These surface electrons have a number of highly unusu-al characteristics: (i) they behave like massless relativistic particles similar to photons (ii) their spin is locked perpendicular to their momentum and (iii) this state is robust against moderate disorder. Understanding and characterizing unique properties of these materials can lead to novel ap-plications such as current induced magnetization or extremely robust quantum memory bits. In this talk, I will first give a brief introduction to these materials and then describe our recent experiments in which we used ultrashort laser pulses to probe and control properties of the topo-logical surface states. Utilizing the short duration of these pulses, we suc-ceeded in capturing femtosecond movies of the electronic energy bands in a three dimensional manner. These movies reveal an exotic hybrid state between electrons and light which was predicted theoretically but has never been observed in solids before.

Tessellated patterns, realistic animals, and curved polygonal shapes are all examples of the beautiful and amazing sculptures that can now be made using Origami, the art of paper folding. This art form has experienced tremendous growth with the advent of mathematical techniques that allow the basic structure of any new sculpture to be plotted out before any folding occurs, and laser cutter technologies that have made it easier to create folds in a variety of materials. In addition to their static properties, Origami sculptures can be designed to have a wide variety of mechanical properties making them responsive and tunable. Here, I will present a work-flow pipeline for materials design that uses Origami as a means of devising basic modular building blocks that can be assembled into larger-scale mechanical meta-materials. We start by working with origami artists to identify and generate candidate folding patterns for study. Next, we develop full-scale models using laser cut Mylar and paper sheets for rapid design, testing, and redesign. Mechanical measurements of these prototypes are combined with numerical simulations to identify the key relations between mechanical properties and geometric structure that give rise to the measured properties. Once a desirable pattern is identified, it is scaled down to a sub-mm tri-layer temperature-responsive polymer sheet using photolithographic techniques. The polymer sheet is capable of folding and unfolding as a function of temperature, and moreover, exhibits similar geometry-driven mechanical properties as the bench top prototypes. Stepping-back, we see this work-flow from design to synthesis as a conceptual tool that will help expedite origami-inspired materials.