****TECHNICAL ABSTRACT**** Over the past 15 years, optical tools to study the time evolution of electronic spin angular momentum have made central contributions to the development of spintronics, a field of study aimed at exploiting the spin degree of freedom of delocalized electrons for classical and quantum information processing and storage in the solid state. But recent times have brought accelerating interest in new classes of materials for which orbital angular momentum becomes the central player. In this proposal the PI introduces an analogous class of ultrafast optical spectroscopies aimed at probing the dynamics of orbital angular momentum in solids. Using optical vortex beams carrying orbital angular momentum, superpositions of these beams, and holographic gratings to manipulate and separate their spatial character, the PI will construct experiments to study the dynamics of optically-excited orbital angular momentum. If successful this project will introduce a valuable tool for studying the salient dynamical features of an emerging class of orbitally coherent materials such as graphene and topological insulators. In addition to training graduate students in advanced optical techniques, this project will also strive to increase the participation and visibility of underrepresented scientists as mentors in a shared equipment facility.
It is no surprise to most people that when a wire is connected across the terminals of a battery, electrical current will flow. And secondary school physics courses teach students that when a magnet is waved nearby a closed loop of wire, current flows in the loop. Electrical generators, for example, utilize this effect to convert mechanical energy into electricity. But when electrical circuits become very small, another entirely different behavior is possible, which has its origins in the wave nature of the electron. Similar to the way quantum mechanics forces atomic orbitals to have discrete energies, nanoscale puddles of electrons in a material cannot occupy an arbitrary configuration. If the puddle is sufficiently small, then the quantum mechanical wave of an electron must smoothly connect to itself in going around the puddle. As a result, the puddle carries small quantum mechanical currents even when the relative position and orientation of an external magnet is held stationary. In this project, the PI will introduce an entirely new type of laser spectroscopy that excites such quantum mechanical currents in a solid and monitors their time evolution. If successful, this project will use these responses to identify solid state materials capable of storing quantum mechanical information in the rotary motion of electrons, with applications to classical and quantum mechanical devices. In addition to training graduate students in advanced optical techniques, this project will also increase the participation and visibility of underrepresented scientists as mentors in a shared equipment facility.
