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Beyond the molecular movie: Dynamics of bands and bonds during a photoinduced phase transition

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Science  16 Nov 2018:
Vol. 362, Issue 6416, pp. 821-825
DOI: 10.1126/science.aar4183

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Physics and chemistry in concert

Shining a short, intense light pulse on a material can cause a transition in both its atomic and electronic structures. The dynamics of the electronic structure in such transitions can be monitored using, for example, time-resolved photoemission spectroscopy. Nicholson et al. observed a photoinduced metal-insulator transition in indium nanowires on a silicon surface. They monitored both the physics and the chemistry of the system after the initial photoexcitation and correlated the closing of the electronic bandgap with the rearrangement of chemical bonds. The results showcase the wealth of information that time-resolved tools can reveal about the dynamics of complex systems.

Science, this issue p. 821

Abstract

Ultrafast nonequilibrium dynamics offer a route to study the microscopic interactions that govern macroscopic behavior. In particular, photoinduced phase transitions (PIPTs) in solids provide a test case for how forces, and the resulting atomic motion along a reaction coordinate, originate from a nonequilibrium population of excited electronic states. Using femtosecond photoemission, we obtain access to the transient electronic structure during an ultrafast PIPT in a model system: indium nanowires on a silicon(111) surface. We uncover a detailed reaction pathway, allowing a direct comparison with the dynamics predicted by ab initio simulations. This further reveals the crucial role played by localized photoholes in shaping the potential energy landscape and enables a combined momentum- and real-space description of PIPTs, including the ultrafast formation of chemical bonds.

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