Eur. Phys. J. B 75, 415-430 (2010)
https://doi.org/10.1140/epjb/e2010-00147-9

sp³ domain in graphite by visible light and photoinduced phase transitions

Solid State Theory Division, Institute of Materials Structure Science, KEK, Graduate University for Advanced Study and CREST JST, 1-1, Oho, Tsukuba, 305-0801, Japan

Corresponding author: ^a knasu@post.kek.jp

Received: 5 January 2010
Revised: 25 March 2010
Published online: 19 May 2010

Abstract

Photoinduced structural phase transition (PSPT)s are reviewed in connection with recent experimental results. There are two key concepts: the hidden multi-stability of the ground state, and the proliferations of optically excited states. Taking the ionic (I)-neutral (N) phase transition in an organic charge-transfer (CT) crystal TTF-CA, as an example, we, briefly look back the essence of its PSPT, in terms of the CT exciton and the N-domain proliferation. Next, we are concerned with the discovery of a new photoinduced phase with inter-layer σ-bonds in a graphite. We will see the mechanism of this nonequilibrium phase transition, in terms of the proliferation of photo-generated inter-layer CT excitations in the visible region. At the Franck-Condon state, the resultant electron-hole pair is quite unstable, being easily dissipated into the two-dimensional electronic continuum, as plus and minus free carriers. However, by a small probability, the electron and the hole are bound as an inter-layer CT exciton. This exciton self-localizes, contracting the inter-layer distance and buckling the six membered ring of graphite, only around it. Thus a tiny sp³ nano-domain appears.