Longitudinal spin-charge responses and collective modes in spin-polarized quantum devices

The generalized longitudinal charge-spin susceptibility functions and the c ollective excitations of spin-polarized quantum structures are investigated within the framework of spin;dependent linear response theory. We evaluate the charge response and the longitudinal spin response to a general extern al disturbance. Exchange-correlation effects between electrons of spin sigm a and sigma' are included by using spin-polarization dependent generalized local field factors. Both the collective charge-density and spin-density ex citations are examined. The present results are compared with the case of a spin-unpolarized system. In contrast to the result for an unpolarized syst em, the mixing of charge and spin responses results in coupled charge;spin excitations in the spin polarized system.