H. Uemura

Publications (6)18.97 Total impact

• Source

  Available from: S. Bonora

  Article: Quantum interference between charge excitation paths in a solid-state Mott insulator

  S Wall, D Brida, S R Clark, H P Ehrke, D Jaksch, A Ardavan, S Bonora, H Uemura, Y Takahashi, T Hasegawa, H Okamoto, G Cerullo, A Cavalleri
  [show abstract] [hide abstract]
  ABSTRACT: Competition between electron localization and delocalization in Mott insulators underpins the physics of strongly correlated electron systems. Photoexcitation, which redistributes charge, can control this many-body process on the ultrafast timescale(1,2). So far, time-resolved studies have been carried out in solids in which other degrees of freedom, such as lattice, spin or orbital excitations(3-5), dominate. However, the underlying quantum dynamics of `bare' electronic excitations has remained out of reach. Quantum many-body dynamics are observed only in the controlled environment of optical lattices(6,7) where the dynamics are slower and lattice excitations are absent. By using nearly single-cycle near-infrared pulses, we have measured coherent electronic excitations in the organic salt ET-F(2)TCNQ, a prototypical one-dimensional Mott insulator. After photoexcitation, a new resonance appears, which oscillates at 25 THz. Time-dependent simulations of the Mott-Hubbard Hamiltonian reproduce the oscillations, showing that electronic delocalization occurs through quantum interference between bound and ionized holon-doublon pairs.
  Nature Physics 02/2011; 7(2):114-118. · 18.97 Impact Factor
• Conference Proceeding: Quantum interference between photo-excited states in a solid-state Mott insulator

  S Wall, D Brida, S R Clark, H P Ehrke, D Jaksch, A Ardavan, S Bonora, H Uemura, Y Takahashi, T Hasegawa, H Okamoto, G Cerullo, A Cavalleri
  [show abstract] [hide abstract]
  ABSTRACT: By exciting with sub-10-fs 1.6-mu m pulses the quasi-one-dimensional Mott insulator ET-F(2)TCNQ, we observe prompt collapse of the Mott gap modulated by 24-THz oscillations of the gap, which are assigned to quantum interference between holon-doublon excitations. (C) 2010 Optical Society of America
  2010 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) AND QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (QELS); 01/2010
• Source

  Available from: Daniele Brida

  Article: Coherent Mott Excitations Captured on the Timescale of Electron Correlations

  S Wall, D Brida, S. R. Clark, H. P. Ehrke, D. Jaksch, A. Ardavan, S Bonora, H. Uemura, Y Takahashi, T Hasegawa, H Okamoto, G. Cerullo, A. Cavalleri
  [show abstract] [hide abstract]
  ABSTRACT: By using nearly-single-cycle optical pulses in the near infrared, we measure the time-dependent optical properties of the Mott insulator ET-F2TCNQ after prompt photo-excitation. We observe a rapid drop in spectral weight at the Mott gap, and oscillations in the optical conductivity, revealing coherent electronic-structural rearrangements on the timescale of electron correlations. A quantum dynamic model based on the Fermi Hubbard Hamiltonian predicts recurrence oscillations between bound and unbound holon-doublon pairs, closely matching the experimentally observed frequency. To date, coherent many body processes of this kind have only been experimentally accessible in ultracold gases, where the correlation energies are re-normalized to lower values and the dynamics is correspondingly slower. We bridge the gap between optics on extreme timescales and the control of strongly correlated quantum gases, and identify the first steps in the coherent response of a Mott insulator. Comment: 4 figures
  10/2009;
• Article: Ultrafast photoinduced melting of spin-Peierls phase in potassium-tetracyanoquinodimethane

  H Uemura, H Matsuzaki, H Okamoto
  [show abstract] [hide abstract]
  ABSTRACT: Ultrafast dynamics of photoinduced melting of spin-Peierls (SP) phase was investigated in K-tetracyanoquinodimethane by using fs pump-probe reflection spectroscopy. It was revealed that the photocarriers are localized with ~70 fs and behave as nonmagnetic impurities, which lead to the melting of the SP phase within ~ 400 fs. In the melting process of the SP phase, several kinds of coherent oscillations were observed, suggesting that the corresponding several phonon modes contribute to the stabilization of the SP phase.
  Journal of Physics Conference Series 03/2009; 148(1):012012.
• Chapter: Clocking the Collapse of a Mott Gap

  S. Wall, D. Brida, H. P. Ehrke, A. Ardavan, S. Bonora, H. Matsusaki, H. Uemura, Y. Takahashi, T. Hasegawa, H. Okamoto, G. Cerullo, A. Cavalleri
  [show abstract] [hide abstract]
  ABSTRACT: We probe the dynamics of band gap collapse in the Mott (electronic) insulator ETF2TCNQ and Peierls (structural) insulator K-TCNQ. The collapse of the Mott gap is a purely electronic process occurring within 20 fs. In the Peierls insulator, the gap collapse takes 300 fs, only after a lattice distortion has relaxed.
  12/2008: pages 167-169;
• Article: Ultrafast charge dynamics in organic one-dimensional Mott insulators

  H. Uemura, H. Matsuzaki, Y. Takahashi, T. Hasegawa, H. Okamoto
  [show abstract] [hide abstract]
  ABSTRACT: Ultrafast charge dynamics in one-dimensional Mott insulators was investigated by femtosecond reflection spectroscopy on organic molecular compounds, K-tetracyanoquinodimethane (TCNQ), Rb-TCNQ, and bis(ethylenedithio)tetrathiafulvalene (ET)-difluorotetracyanoquinodimethane (F2TCNQ). In K- and Rb-TCNQ, photocarriers are localized as polarons with ∼70 fs and recombine with a few ps. In ET-F2TCNQ, photocarriers lead to a metallic state and decay with ∼200 fs. Such differences of the charge dynamics can be explained by taking account of the different magnitudes of the electron-lattice interactions in the three compounds.
  Physica B: Condensed Matter.