Terahertz Dynamics Of Lattice Vibrations In Au/Cdte Plasmonic Crystals: Photoinduced Segregation Of Te And Enhancement Of Optical Response

The excitation of coherent optical phonons in solids provides a pathway for ultrafast modulation of light on a sub-ps time scale. Here, we report on efficient 3.6 THz modulation of light reflected from hybrid metal/semiconductor plasmonic crystals caused by lattice vibrations in a few-nm-thick layer of elemental tellurium. We observe that surface plasmon polaritons contribute significantly to the photoinduced formation of the tellurium layer at the interface between a telluride-based II-VI semiconductor, such as (Cd, Mg) Te or (Cd, Mn) Te, and a one-dimensional gold grating. The change in interface composition is monitored via the excitation and detection of coherent optical tellurium phonons of A(1) symmetry by femtosecond laser pulses in a pump-probe experiment. The patterning of a plasmonic grating onto the semiconductor enhances the transient signal which originates from the interface region. This allows one to monitor the layer formation and observe the shift of the phonon frequency caused by confinement of the lattice vibrations in the nm-thick segregated layer. Efficient excitation and detection of coherent optical phonons by means of surface plasmon polaritons are evidenced by the dependence of the signal strength on polarization of the pump and probe pulses and its spectral distribution.