Correlation-gap oscillations in an organic Mott-insulator induced by phase locked excitation of local molecular vibrations R. Singla 1 , G. Cotugno 1,2 , S. Kaiser 1 , M. Först 1 , M. Mitrano 1 , H. Y. Liu 1 , A. Cartella 1 , C. Manzoni 1,4 , H. Okamoto 5 , T. Hasegawa 6 , S. Clark 2,3 , D. Jaksch 2,3 , A. Cavalleri 1,2 1 Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany 2 Department of Physics, Oxford University, Clarendon Laboratory, Parks Road, OX1 3PU Oxford, United Kingdom 3 Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543, Singapore 4 IFN-CNR, Dipartimento di Fisica-Politecnico di Milano, Milan, Italy 5 Department of Advanced Material Science, University of Tokyo, Chiba 277-8561, Japan 6 National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8562, Japan Email: rashmi.singla@mpsd.mpg.de, stefan.kaiser@mpsd.mpg.de, andrea.cavalleri@mpsd.mpg.de Abstract: Mid-infrared pulses with stable carrier-envelope phase offset are used to drive molecular vibrations in the charge transfer salt ET-F 2 TCNQ, a prototypical one-dimensional Mott insulator. The vibrations modulate the local orbital wavefunction and hence the Coulomb integral at each site. The optical gap, probed at the charge transfer resonance by 1.7 m wavelength pulses of 10 fs duration, oscillates at twice the frequency of the vibrational mode, revealing quadratic coupling of the local charge density to the molecular mode. The experiments reported here show how electron correlations can be modulated by coherent modulation of local degrees of freedom, different from mechanisms discussed to date involving nonlinear excitation of collective phonon modes.