Dynamics for unstable self-induced plasma field of electrons driven by a transient electric field in a quantum wire

In this work, coupled field-gauge-invariant self-consistent quantum-kinetic theory in combination with Maxwell equations are established and applied to study ultrafast dynamics of a transient-field driven and photoexcited electron plasma induced by an incident infrared pulse-laser field. Our study reveals that the self-induced plasma-field instability occurs in a quantum-wire system once the transient electric field points to the opposite direction of the pulse-laser-field wave vector. This new effect leads to amplification of an induced plasma field. However, the physical mechanism behind this instability is quite different from earlier reported enhancement of a collective-excitation mode. Here, the latter is enabled by introducing a Doppler-shifted plasmon frequency under a finite drift velocity of electrons, as calculated based on a linear-response theory [e.g., K. Kempa et al., Phys. Rev. B 43, 9273 (1991)]. Dynamically, it is also different from the well-known classical two-stream plasma-fluid instability [e.g., T. M. O'Neil et al., Phys. Fluids 11, 1754 (1968)]. Interestingly, such a transient-field driven instability of a plasma field within a translationally invariant system enables generating a coherent terahertz-radiation wave from a small device with its size comparable to the driving-field wavelength. In current study, the field-gauge invariant semiconductor Bloch equations have been employed [e.g., A. M. Parks et al., Phys. Rev. Lett. 131, 236902 (2023)]. Furthermore, a unique mechanism for amplifying a self-induced plasma field has been identified and analyzed fully based on our self-consistent field-gauge-invariant quantum-kinetic equations for transient-field-driven and laser-excited electron plasma within a quantum-wire system. It is expected that such a unique physical phenomenon is able to generate a tunable high-intensity coherent terahertz-radiation wave.