CAREER: Real-Time First-Principles Approach to Understanding Many-Body Effects on High Harmonic Generation in Solids

Yale University, New Haven CT

Investigators

Abstract

Nontechnical Summary This award supports research, education, and outreach activities focused on understanding how interactions between electrons change the way that materials behave when exposed to very strong electromagnetic fields. Strong electromagnetic fields interact with materials in a highly nonlinear way. One phenomenon that arises in these high fields is high harmonic generation—a process where low-energy light is absorbed by a material and combined to produce light at energies that are integer multiples (or harmonics) of the incoming light. Such high harmonic generation is fundamental for the development of ultrafast light sources that can be used to probe the physics of electronic and atomic motion on very short timescales. Most existing sources of high harmonic generation rely on generation from gases of atoms and molecules, where the allowed energy levels of the electrons are discrete. Extending these processes from the gas phase to crystalline solids introduces greater flexibility in the energy ranges that can be accessed by the incoming and generated light. The generation of high harmonic light in solids can also potentially be used as a tool for characterizing the behavior of electrons in these solids. However, the interpretation of high harmonic spectra in solids is highly challenging due to the complicated interplay of electronic and atomic motion that contribute to the yield of outgoing light under different generation conditions. This project aims to develop, implement, and apply new theoretical and computational tools to aid in understanding the role of electron motion and interactions in high harmonic generation from solids. The developed methods will be applied to study high harmonic generation in low-dimensional solids where electron interactions are expected to be strong. This project supports a postdoctoral researcher and the education of a graduate student. Additionally, this project will integrate research, education, and mentoring with a scaffolded outreach program designed to broaden the participation of groups that are historically under-represented in science and engineering. The PI will develop a new undergraduate materials science curriculum and a summer materials science workshop and offer a yearly summer internship for students from the New Haven public school system. The proposed outreach includes a rigorous data collection component that will allow the impact of the program to be assessed. TECHNICAL SUMMARY This award supports research, education, and outreach activities focused on understanding many-body effects in nonperturbative high harmonic generation. High harmonic generation in solids is foundational for the creation of new attosecond light sources across the extreme ultraviolet regime and holds promise as an all-optical probe of materials’ bandstructure and topology. However, theory that can describe nonperturbative high harmonic generation in real materials is still nascent, especially when it comes to a quantitative understanding of many-body effects. This project aims to develop and apply a new ab initio method based on the Keldysh formalism for nonequilibrium many-body states to understand many-body effects in high harmonic generation and other nonlinear spectroscopies beyond the perturbative regime. The method is built on the time-dependent adiabatic GW approach (here, G stands for the one-particle Green’s function and W is the screened Coulomb interaction), where the one-particle density matrix is coupled to an external field and propagated in time with the ab initio GW self-energy. The PI and her team will apply this approach to (1) to understand signatures of topology, spin, polarization textures, and exciton effects in high harmonic spectra by performing calculations on a testbed of two-dimensional materials, where complex factors like exciton binding energy, screening, and symmetry can be more easily isolated; and (2) understand the limits of our computational techniques and constituent approximations. This project supports a postdoctoral researcher and the education of a graduate student. Additionally, this project will integrate research, education, and mentoring with a scaffolded outreach program designed to broaden the participation of groups that are historically under-represented in science and engineering. The PI will develop a new undergraduate materials science curriculum and a summer materials science workshop and offer a yearly summer internship for students from the New Haven public school system. The proposed outreach includes a rigorous data collection component that will allow the impact of the program to be assessed. 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.