CAREER:The Nonlinear Electrodynamics of Weyl Semimetals

Temple University, Philadelphia PA

Investigators

Abstract

Nontechnical Abstract: The march of progress in electronic devices is invariably toward smaller, faster and more energy efficient. Unfortunately, the fundamental limitations of the materials that comprise currently made devices has recently started to threaten the rate of technological progress. A novel class of “topological” materials, holds great promise to be a truly paradigm shifting platform that can help break the impending logjam of technological advancement. However, the very properties that make these materials unique are not straightforward to observe directly. This makes deliverable application of new technologies based on this platform difficult. The current project aims to develop methods that probe these unique characteristics. Simultaneously, the educational component of this project is designed to increase the number of students in Pennsylvania schools that study physics through a two-component program named “Physics Forward.” The first element of this activity comprises a seminar series for high school students on engaging topics in physics. The second component creates a class for high school teachers to teach the topics of this proposal in layperson's terms as a component of a larger physics instructor certification program to be run at Temple University. Technical Abstract: The overarching goal of this project is to experimentally measure the defining characteristics of Weyl semimetals using nonlinear optical techniques through three complementary sets of specific aims. The first aim is centered on using the circular photogalvanic effect, a nonlinear optical process in which a laser injects a photocurrent into the sample, in order to generate current transients in the surface Fermi arcs whose emitted radiation is then detected using the standard technique of electro-optic sampling. The (001) face of the chiral Weyl semimetal RhSi is studied here as an ideal testbed system for this approach due to the large energy bandwidth spanned by the Fermi arcs on this face. The second aim of this research is to establish difference frequency generation as a direct probe of topological order. Through its ability to provide an emitted photon resonant with topological energy bands from two higher energy incoming photons, this technique is used to directly measure Berry quantization in RhSi, Berry quantization in TaAs using the chiral anomaly, and the surface Fermi arc responses of both TaAs and RhSi. The third and final aim of this project is to leverage the unique bandstructure of RhSi to perform ultra-efficient energy transfer from a strong, near infrared field into a weaker mid- or far-infrared field using Floquet drives in this material, and reveal the energy transfer rate as proportional to its quantized topological charge. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.