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Applied Physics A, 2013. DOI: 10.1007/s00339-013-7929-3.
Takayuki Suwa, Akira Ishikawa, Kazuharu Uchiyama, Takashi Matsumoto, Hirokazu Hori, Kiyoshi Kobayashi.
Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, 4-3-11 Takeda, Kofu, Yamanashi, 400-8511, Japan
Abstract
Optical near-field (ONF) phenomena observed in nanoscale systems have been applied to nano-fabrication and nano-photoelectronic devices for the last decade. Excitation transfer (ET) is an elementary process caused by ONF interaction localized at the nanoscale in real space. Recently, we have observed spin-dependent ET controlled by an external field and discovered the sign of assistance of phonons. In this work, we elucidate that the assistance of coherent phonons in ET originates from two types of mechanism: energy resonance between exciton levels renormalized by phonon effects and enhancement by phase matching between coherent oscillation of populations and phonon oscillation. This study will stimulate the development of the application of ET via a ONF to nano-photoelectronic devices.
Fig. : (a) Schematic drawing of an experimental sample consisting of two quantum wells, QW1 (ZnCdMnSe) and QW2 (ZnCdSe); (b) energy diagrams of a diluted magnetic semiconductor quantum well (DMSQW) and a nonmagnetic semiconductor quantum well (NMSQW), respectively; (c) a theoretical model for excitation transfer between double quantum wells (DQW), QW1 and QW2, via optical near-field interaction assisted by phonons. double quantum wells (DQW), QW1 and QW2, via optical near-field interaction assisted by phonons.
Fig. 2 Two types of mechanism of the coherent phonon-assisted excitation transfer.
Type 1 (left column): excitation transfer enhanced by the energy resonance between exciton levels renormalized by phonons in QW1 and QW2, respectively.
Type 2 (right column): excitation transfer enhanced by a collective oscillation of Rabi oscillation of populations in QW1 and QW2, and phonon oscillations. In each column,
(a) population dynamics in QW1 and QW2, (b) time evolution of the exciton energy difference in QW1 and QW2, (c) temporally modulated Rabi frequency are shown.
