Resonant coupling of collective intra- and intersubband excitations in a parabolically confined electron system

A wide electron system as realized in modulation-doped parabolic quantum wells is used to investigate the resonant interaction between intra- and intersubband plasmonic excitations. In contrast to a conventional quasi-two-dimensional electron system, both excitations have about the same resonance energy at finite wave vector due to a relatively low subband spacing. We use a perpendicular magnetic field to tune the intrasubband plasmon such that it energetically degenerates with the intersubband mode. In the electrical quantum limit no mode coupling is observed, whereas for the case of two occupied subbands a strong resonant interaction of both modes is reflected in anticrossing behavior.