| The resonant transitions between chiral subbands in two-dimensional electron systems can lead to nontrivial observable modifications of some of the optical and electronic properties of these systems. We study these effects in three two-dimensional chiral electron liquids: two-dimensional electron liquids with spin-orbit interactions, carbon monolayers, or graphene, and spin-split surface states on noble metal-dielectric interfaces.;Intersubband transitions can also affect the spectrum of collective charge oscillations, or plasmons, in chiral systems. In graphene, the weak attractive Coulomb interactions between an electron in the conduction band that is excited from the valence band with the hole it leaves behind leads to the lowering of the energy for which absorption of external fields is allowed. Remarkably, it also leads to the prediction of the existence of a collective mode of charge oscillations, whereas this mode is absent if the interactions are not taken into account.;The intersubband transitions can even manifest themselves in the plasmon spectrum at the interface of some noble metals with dielectric materials. The presence of spin-split surface states on the surface of some bulk noble metals can be observed through the enhancement of certain properties due to resonances from intersubband transitions. For example, the impedance of incident radiation on the interface exhibits a resonant feature, and the surface plasmon spectrum is resonantly modified in the region of frequencies corresponding to the frequency of the intersubband transitions.;For instance, it is shown that the response of an electron liquid with spin-orbit interactions to a homogeneous electric field, where more than one electron-hole pair is excited, is dependent on the strength of the electron-electron interactions, and therefore can be used to probe many-body effects in such systems. This dependence is derived for both short-range and long-range interactions. In the absence of spin-orbit interactions, on the other hand, this effect is completely absent. |
