Coherent Excitonic Wavepackets in Two-Dimensional Square Dot Arrays Driven by an In-Plane Uniform Electric Field

We investigate the evolution behaviour of electron-hole pair wavepacket in optically excited square quantum-dot arrays driven by in-plane (x-y plane) uniform electric field E (viz, E = E_xe_x + E_ye_y, e_x, e_y are unit vectors along x and y directions respectively), in the time domain. It is found that if the ratio of the x-component electric field E_x to the y-component electric field E_y is a rational p/q (p and q being coprime integer numbers), the wavepackets undergo a time-periodic breathing mode, with the period 2πp/ω_Bx, where ω_Bx = eE_xa/ħ, with a being the lattice constant of square dot arrays, ħ being Planck's constant, e being the electron charge. This finding provides a time-domain demonstration of the recent spectral result Phys. Rev. Lett. 86 (2001) 3116.