PROPAGATION OF LOW-FREQUENCY PLASMONS AND e-h EXCITATIONS

Over the past year, research on the dynamic behavior of quasiparticles using ultrafast spectroscopy has become a major topic in solid-state physics [1-12]. By utilizing ultrafast laser pulses, researchers have been able to generate and monitor the dynamic oscillations of electrons. The integration of ultrafast laser pulse technology with scanning tunneling microscopy (STM) has led to the development of a new microscopy technique that allows for the real-space imaging of transient carrier dynamics in nanostructures [10, 11]. Coherent nanoimaging and nanospectroscopy have also observed ultrafast coherent dynamics and related nanoscale phenomena with nanometer and femtosecond temporal resolutions [11, 13-15]. With the advent of near-field optical microscopes, there has been an increased interest in the real-space and time propagation of plasmons [13-16]. The Fourier transform STM provides a method to determine the Fermi surface directly by measuring standing-wave patterns around defects in a metal [17-19]. Efficiently converting the transient carrier response into measurable electrical signals is crucial for realizing the dynamic properties of quasiparticles governed by single-particle or collective excitations. Plasmon oscillations in conducting materials can produce large optical field confinement and enhancement, highlighting their potential for practical applications….