Terahertz-field-driven sub-picosecond optical switching enabled by large third-order optical nonlinearity in a one-dimensional Mott insulator

Sub-picosecond modulation of the optical reflectivity (R) using terahertz electric-field (ETHz) pulses was achieved in a typical one-dimensional Mott insulator, the bromine-bridged nickel compound, [Ni(chxn)2Br]Br2 (chxn: cyclohexanediamine). The reflectivity change (ΔR/R) at around the Mott-gap transition peak (∼1.3 eV) was ∼1% for ETHz ∼45 kV/cm, and proportional to the square of ETHz. The relaxation time of ΔR/R was under 0.1 ps, enabling optical switching with a high repetition rate in the near-infrared region. The electric-field and probe-energy dependences of ΔR/R demonstrate that the modulation is due to large third-order optical nonlinearity of one-dimensional Mott insulators.