CDS&E: Ab Initio Ultrafast Dynamics of Spin, Valley and Charge in Quantum Materials

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

This grant is being funded by the Condensed-Matter and Materials Theory program in the Division of Materials Research and by the Chemical Theory, Models, and Computational Methods program in the Division of Chemistry. Nontechnical Summary The promise of quantum computers to perform calculations beyond the reach of any current or conceivable non-quantum computer has made them one of the nation's highest research priorities. This award supports computational research and education on the motion of electrons in quantum materials. Several recently-discovered materials exhibit the potential to store quantum information in individual electrons that may hold the key to the next generation of quantum computers and quantum communication. Realizing the full potential of these materials requires precise understanding of how long quantum information can be stored in electron spins and how it disappears eventually by interacting with the vibrations of atoms in the material. The investigators will develop a computational methodology to simulate quantum electron motion on large supercomputers. They will use this technique to predict how electron spin changes over times ranging from femtoseconds to microseconds in several promising materials, such as lead halide perovskites, containing heavy atoms that couple spin to the movement of electrons. Electrons in transition-metal dichalcogenides, another alternative for storing quantum information, can be found in multiple so-called "valleys;" the investigators will also study how electron valley and electron spin couple. For each of these materials, they will simulate the interaction of these quantum states with extremely short laser pulses to interpret experimental measurements of spin and valley dynamics. This award will also support the team's effort in increasing participation and representation of women in STEM disciplines, especially in the physical sciences. By integrating simulations into intuitive visualizations using augmented reality, they will make electron dynamics understandable to undergraduate and high school students. Finally, this project will strengthen the research infrastructure at UCSC, a Hispanic Serving Institution. Technical summary The goal of this research project is to predict quantitatively quantum dynamics of electrons with spin, valley, or other internal degrees of freedom, entirely from first principles. The research team will develop a novel computational methodology and associated massively-parallel open-source software rapidly to evolve density matrices of quantum materials in a Lindbladian formulation, with ab initio treatment of electron-electron, electron-phonon, and electron-photon interactions. This will facilitate calculation of both coherent dynamics and dephasing of spin or valley polarization, along with their experimental signatures in ultrafast spectroscopy. Using this technique, they will investigate spin dynamics in systems with strong spin-orbit coupling and Rashba splitting such as lead halide perovskites and ferroelectric oxides, and valley dynamics in layered transition metal dichalcogenides. This fundamentally new predictive capability will facilitate quantitative analysis of ultrafast optical and free-electron laser measurements with linear and circular polarization, and accurate predictions of spin relaxation of quantum materials. This will be critical for the design and discovery of new material platforms for spintronics, valleytronics and quantum information. The proposed work will arm the materials research community with first-principles quantum dynamics methods in open-source software. These will include a hierarchy of methods that keep track of different levels of coherence, with corresponding computational requirements ranging from a small computer cluster to future exascale supercomputers. It will thereby deliver a key computational technique necessary for predicting coherent and incoherent ultrafast dynamics in quantum materials, extending significantly beyond the capabilities of existing first-principles methods. The work funded in this project responds directly to one of NSF's 10 Big Ideas, the Quantum Leap, by facilitating quantitative simulation of spin relaxation and carrier dynamics critical for quantum information science. The educational activities associated with this project aim to increase participation and representation of women in STEM disciplines, especially in the physical sciences. It will expand the reach of materials simulations to K-12 education through the platform of augmented reality. This project will also strengthen the research infrastructure at UCSC, a Hispanic Serving Institution. 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.