Topological Physics and Light Matter Interactions: From Floquet Topological Insulators to Solar Cells

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NON-TECHNICAL SUMMARYThe Division of Materials Research and the Division of Physics contribute funds to this award which supports theoretical research and education focused on means to stabilize and utilize topological behavior through light-matter interactions in a variety of systems. Topological insulators possess some amazing properties such as the ability to conduct electricity without dissipation at their boundaries while being insulating through their interior. The research which will be carried out under this award is geared toward extending concepts of topological behavior of matter when it interacts with light. This presents a fertile ground for fundamental and applied research. The research will concentrate on three themes. The first is to employ topological insulator surfaces for energy harvesting and detection of infra-red light. The second is to use light to turn an ordinary insulator into a topological insulator. The third is to create unique edge states in a hybrid system of a semiconductor in a cavity that could bridge semiconductor and optical technologies. This research has the potential of introducing new techniques for energy harvesting and light detection and paving the way to new photonic devices based on topological principles. The award will allow training of graduate students and postdocs in an interdisciplinary research environment at the intersection of materials physics and optics. The PI will involve undergraduate students in this research and incorporate the research material into the undergraduate level course that he has developed at Caltech.TECHNICAL SUMMARYThe Division of Materials Research and the Division of Physics contribute funds to this award which supports theoretical research and education focused on means to stabilize and utilize topological behavior through light-matter interactions in a variety of systems. The first part of the project is focused on turning the surface of three-dimensional (3D) topological insulators into a photovoltaic platform aimed at the elusive mid-wavelength infrared spectrum. The surface electrons of 3D topological insulators typically have a minute photocurrent response to incident light in spite of the fact that many electron-hole pairs form. The PI will exploit the spin-orbit locking on the surface to turn it into a photocurrent rectifier. This can be done using a magnetic grating deposited on the surface which should result in a substantial photocurrent response to circularly polarized light. The PI will consider the manifestations of this effect in realistic topological insulators, its optimization with respect to the magnetic pattern deposited, and its extension to other systems, such as two-dimensional (2D) topological insulators and 2D quantum wells with Rashba interaction. In the second part the PI will study ways to induce topological behavior in trivial semiconductors using coherent light. Electrons in semiconductors driven into a topological phase exhibit a non-equilibrium energy distribution determined by the strength of the drive and various relaxation mechanisms. By deriving these distributions, the PI will investigate under what circumstances the non-equilibrium effects do not obstruct the topological behavior of the driven system, and analyze schemes to detect this so-called Floquet topological phase.The third part of the project is focused on the possibility of creating topological polariton states in optical waveguides coupled to trivial semiconductors. Relying on the idea of the Floquet topological insulator, the PI will examine whether it is possible to have a topological bound state of a cavity photon and an exciton in a topologically trivial semiconducting quantum well. A topological polariton state may exhibit strongly enhanced lifetimes, as well as could be used as a nanophotonic isolator. This research has the potential of introducing new techniques for energy harvesting and light detection and paving the way to new photonic devices based on topological principles. The award will allow training of graduate students and postdocs in an interdisciplinary research environment at the intersection of materials physics and optics. The PI will involve undergraduate students in this research and incorporate the research material into the undergraduate level course that he has developed at Caltech.