Research Highlights

Photo-induced phase transitions

A combination of ultrafast electron diffraction and density functional theory simulation tracks the time evolution of TaTe2 after intense near-infrared excitation and observes light-induced melting of its charge and lattice orders, and the subsequent thermalization into a hot superstructure phase. This work demonstrates that light can be used to induce structural and electronic changes in this material, and paves the way for light-driven control of TaTe2 for ultrafast switching applications.

[1] Ultrafast optical melting of trimer superstructure in layered 1T′-TaTe2, Communications Physics 4, 152 (2021).

Coherence properties of color center defects

Color centers, which are light-emitting defects in a host crystal, are a promising route for realizing quantum detectors, quantum single-photon sources, quantum networks, and other devices in quantum information sciences (QIS). Our group performs first-principles calculations of color-center coherence properties in silicon and other host materials. Most recently we have studied the connection between spin and localization properties of defects [1], developed methods for computing phonon-based dephasing times [2], and quantified the amount of inhomogeneous broadening resulting from novel high-energy synthesis methods[3]. Our current work in this area focuses on understanding the effects of local strain and disorder on defect properties, and computing the Stark shift for certain defects in the presence of electric fields.

[1] Effect of Localization on Photoluminescence and Zero-Field Splitting of Silicon Color Centers, Phys. Rev. B 106, 134107 (2022) .

[2] Phonon Induced Spin Dephasing Time of Nitrogen Vacancy Centers in Diamond from First Principles, arxiv:2209.11412 (2022).

[3] Defect engineering of silicon with ion pulses from laser acceleration, arxiv:2203.13781 (2022).

Tight-binding methods for complex nonlinear materials

By using first-principles based tight-binding methods, we access the wide span of time and length scales responsible for non linear processes in complex quantum materials. We investigate the impact of electron-phonon, electron-electron, and electron-spin interactions on these processes. Recently, we reported a new strategy for enhancing the bulk photovoltaic effect (BPVE) using light-induced phase transitions. Using real-time simulations, we showed that a strongly correlated system displays strong photocurrent enhancement when it is driven into hidden magnetic phase transition (see right-figure). This phenomenon is highly non-perturbative, and lies outside the previously studied perturbative framework of shift and ballistic currents used in the field of BPVE [1].

[1] Nonperturbative study of bulk photovoltaic effect enhanced by an optically induced phase transition, Phys. Rev. B 105, 094307 (2022).