title: High-energy side-peak emission of exciton-polariton condensates in high density regime.
abstract: In a standard semiconductor laser, electrons and holes recombine via stimulated emission to emit coherent light, in a process that is far from thermal equilibrium. Exciton-polariton condensates-sharing the same basic device structure as a semiconductor laser, consisting of quantum wells coupled to a microcavity-have been investigated primarily at densities far below the Mott density for signatures of Bose-Einstein condensation. At high densities approaching the Mott density, exciton-polariton condensates are generally thought to revert to a standard semiconductor laser, with the loss of strong coupling. Here, we report the observation of a photoluminescence sideband at high densities that cannot be accounted for by conventional semiconductor lasing. This also differs from an upper-polariton peak by the observation of the excitation power dependence in the peak-energy separation. Our interpretation as a persistent coherent electron-hole-photon coupling captures several features of this sideband, although a complete understanding of the experimental data is lacking. A full understanding of the observations should lead to a development in non-equilibrium many-body physics.
authors.affiliation: National Institute of Informatics, Hitotsubashi 2-1-2, Chiyoda-ku, Tokyo 101-8430, Japan.|E. L. Ginzton Laboratory, Stanford University, 348 Via Pueblo, Stanford, California 94305, USA.|The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan.|Center for Emergent Matter Science, RIKEN, 2-1 Hirosawa, Wakoshi, Saitama 351-0198, Japan.|Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama, Kanagawa 240-8501, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Horikiri
authors.affiliation: Center for Emergent Matter Science, RIKEN, 2-1 Hirosawa, Wakoshi, Saitama 351-0198, Japan.|Department of Physics, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Yamaguchi
authors.affiliation: The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan.|Department of Physics, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Kamide
authors.affiliation: National Institute of Informatics, Hitotsubashi 2-1-2, Chiyoda-ku, Tokyo 101-8430, Japan.|The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Matsuo
authors.affiliation: New York University, 1555 Century Ave, Pudong, Shanghai, 2002122, China.|NYU-ECNU Institute of Physics at NYU Shanghai, 3663 Zhongshan Road North, Shanghai 200062, China.|National Institute of Informatics, Hitotsubashi 2-1-2, Chiyoda-ku, Tokyo 101-8430, Japan.
authors.forename: Tim
authors.initials: T
authors.lastname: Byrnes
authors.affiliation: Center for Emergent Matter Science, RIKEN, 2-1 Hirosawa, Wakoshi, Saitama 351-0198, Japan.
authors.forename: Natsuko
authors.initials: N
authors.lastname: Ishida
authors.affiliation: Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Löffler
authors.affiliation: Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.|SUPA, Schoold of Physics and Astronomy, University of St Andrews, KY16 9SS, United Kingdom.|National Institute of Informatics, Hitotsubashi 2-1-2, Chiyoda-ku, Tokyo 101-8430, Japan.
authors.forename: Sven
authors.initials: S
authors.lastname: Höfling
authors.affiliation: Research Center of Integrative Molecular Systems (CIMoS), Institure for Molecular Science, National Institutes of Natural Sciences, 38 Nishigo-Naka, Okazaki, Aichi 444-8585, Japan.|Institute for Quantum Studies, Chapman University, 1 University Dr., Orange, California 92866, USA.|Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8503, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Shikano
authors.affiliation: Department of Physics, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan.|Photon Pioneers Center, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Ogawa
authors.affiliation: Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
authors.forename: Alfred
authors.initials: A
authors.lastname: Forchel
authors.affiliation: National Institute of Informatics, Hitotsubashi 2-1-2, Chiyoda-ku, Tokyo 101-8430, Japan.|E. L. Ginzton Laboratory, Stanford University, 348 Via Pueblo, Stanford, California 94305, USA.|The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan.|Center for Emergent Matter Science, RIKEN, 2-1 Hirosawa, Wakoshi, Saitama 351-0198, Japan.|ImPACT Program, Japan Science and Technology Agency, 7 Gobancho, Chiyoda-ku, Tokyo 102-0076, Japan.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Yamamoto