Ultrafast zero balance of the oscillator-strength sum rule in graphene

Jaeseok Kim, Seong Chu Lim, Seung Jin Chae, Inhee Maeng, Younghwan Choi, Soonyoung Cha, Young Hee Lee, Hyunyong Choi

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8 Citations (Scopus)


Oscillator-strength sum rule in light-induced transitions is one general form of quantum-mechanical identities. Although this sum rule is well established in equilibrium photo-physics, an experimental corroboration for the validation of the sum rule in a nonequilibrium regime has been a long-standing unexplored question. The simple band structure of graphene is an ideal system for investigating this question due to the linear Dirac-like energy dispersion. Here, we employed both ultrafast terahertz and optical spectroscopy to directly monitor the transient oscillator-strength balancing between quasi-free low-energy oscillators and high-energy Fermi-edge ones. Upon photo-excitation of hot Dirac fermions, we observed that the ultrafast depletion of high-energy oscillators precisely complements the increased terahertz absorption oscillators. Our results may provide an experimental priori to understand, for example, the intrinsic free-carrier dynamics to the high-energy photo-excitation, responsible for optoelectronic operation such as graphene-based phototransistor or solar-energy harvesting devices.

Original languageEnglish
Article number2663
JournalScientific reports
Publication statusPublished - 2013

Bibliographical note

Funding Information:
The work at Yonsei was supported by the Basic Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. 2011-0013255), the NRF grant funded by the Korean government (MEST) (NRF-2011-220-D00052, No. 2011-0028594, No. 2011-0032019) and the LG Display Academic Industrial Cooperation Program. S. C. Lim and Y. H. Lee at SKKU are grateful for the support from the Research Center Program of IBS.

All Science Journal Classification (ASJC) codes

  • General


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