Nonequilibrium Control of Magnetism and Topology Through Selective Phonon Excitations

Northeastern University, Boston MA

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports research and educational activities with an aim to understand and predict novel regimes of matter in quantum materials. The PI will focus his theoretical research on materials driven out-of-equilibrium from illumination by lasers of different light frequencies and polarization. The high purity light of a laser, which is very nearly of a single frequency in contrast to light from the sun or a light bulb, allows one to selectively deposit energy into the different (e.g. lattice, electronic, magnetic) degrees of freedom of a solid material. Because these different degrees of freedom interact with one another, energy deposited in one will ultimately be distributed among the others after some time, but at intermediate times interesting non-equilibrium phenomena can result. The goal of this project is to uncover interesting electrical and magnetic possibilities theoretically, and help guide experimental groups in their realization in the laboratory. Ultimately, this research may enable new quantum technologies based on light control of matter, including sensing, computing, and communication applications. In addition, this project will support the training of graduate and undergraduate students through direct involvement with the PI in the research described. The PI will continue to deliver a wide range of public lectures with a focus on pre-college students from historically underrepresented backgrounds who have had limited exposure to theoretical physics and/or quantum sciences. Some of these lectures will be delivered through Northeastern University’s Center for STEM Education. The PI will participate in the Building Bridges Program at Northeastern, an interactive day to introduce prospective college students to the sciences and engineering, and the Young Scholars program at Northeastern, a 6-week intensive summer program where rising high-school seniors work on cutting edge research problems and receive mentoring from faculty and university students. TECHNICAL SUMMARY This award supports research and educational activities with an aim to understand and predict novel regimes of matter in quantum materials out-of-equilibrium. The PI will theoretically study the influence of laser-induced lattice changes on the electronic states of correlated electronic materials with strong spin-orbit coupling. The project will substantially extend equilibrium studies of systems with both strong spin-orbit coupling and electronic correlations to the non-equilibrium regime. By directly targeting selected phonon modes in a material with light, heating effects can be minimized, and coherent electronic and magnetic responses generated. Topological transitions, including higher order topological states, in the electronic and magnon band structures and redistribution of Berry curvature in the Brillouin zone will be a focus, as well as phase transitions/phase stabilization of unusual charge-ordered, magnetically-ordered, and superconducting states. Of particular interest will be nonlinear effects that may be induced in the materials through intense light. Nonlinear phononic studies and effects beyond the linear response regime (such as higher harmonic generation) will be studied as a means to drive and detect novel physical regimes and excitations created by intense, low-frequency light. The PI will use complementary theoretical methods that start from both the strong coupling limit and the weak coupling regime to explore the link between laser-induced lattice changes and electronic/magnetic property changes. Numerical and analytical approaches, including model Hamiltonian and first-principles studies, along with symmetry arguments will be employed. In addition, this project will support the training of graduate and undergraduate students through direct involvement with the PI in the research described. The PI will continue to deliver a wide range of public lectures with a focus on pre-college students from historically underrepresented backgrounds who have had limited exposure to theoretical physics and/or quantum sciences. Some of these lectures will be delivered through Northeastern University’s Center for STEM Education. The PI will participate in the Building Bridges Program at Northeastern, an interactive day to introduce prospective college students to the sciences and engineering, and the Young Scholars program at Northeastern, a six-week intensive summer program where rising high-school seniors work on cutting edge research problems and receive mentoring from faculty and university students. 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.