Optically-controlled phonon-specific phase transitions from graphite to diamond

Controlling phase transition processes and the atomic structure of new states with light has emerged as a highly challenging frontiers in condensed matter physics and materials science. The conversion of graphite to diamond typically relies on high-pressure and high-temperature conditions, while the advent of ultrafast laser has opened entirely new possibilities for dynamically controlling such structural transformation under non-thermodynamic state. Herein, employing state-of-the-art first-principles non-adiabatic molecular dynamics simulations, we elucidate ultrafast pathways of light-induced graphite-to-diamond phase transition and reveal the laws governing the selective formation of cubic or hexagonal diamond, as well as their subsequent structural evolution, by regulating laser parameters. Such optically controlled diamond formation stems from early-stage structural reconstruction driven by electron-phonon couplings and indirect excitation of specific phonon modes (e.g. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mi>B</mml:mi></mml:mrow> <mml:mrow><mml:mn>3</mml:mn> <mml:mi>g</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msubsup> </mml:math> modes) via phonon-phonon couplings. The competition between newly generated phonons from indirect excitation constitutes the key factor determining the fine structure of final product. This work not only demonstrates effective modulation of structural phase transition through photoinduced non-thermal pathways, but also provides important strategy for efficient and eco-friendly material synthesis via optical control.