Degenerately doped metal oxide nanocrystals have emerged as infrared plasmonic materials with promising applications in optoelectronics, surface-enhanced infrared spectroscopies, and sensing. They also have potential for technological applications in electronics and photonics owing to the possibility of coupling between plasmon and exciton in the absence of a heterojunction. Here, we demonstrate the control of excitonic splitting in In 2 O 3 nanocrystals upon excitation with circularly polarized light in an external magnetic field by simultaneous control of the electronic structure of donor defects and the nanocrystal host lattice. Using variable-temperature− variable-field magnetic circular dichroism spectroscopy, we show that the nanocrystal band splitting has two distinct contributions in plasmonic In 2 O 3 nanocrystals. Temperature-independent splitting arises from the cyclotron magnetoplasmonic modes, which impart angular momentum to the conduction band excited states near the Fermi level, and increases with the intensity of the corresponding plasmon resonance. Temperature-dependent splitting is associated with the localized electron spins trapped in defect states. The ratio of the two components can be controlled by the formation of oxygen vacancies or introduction of aliovalent dopants. Using these experimental results in conjunction with the density functional theory modeling, relative contribution of the two mechanisms is discussed in the context of the perturbation theory taking into account energy separation between the nanocrystal excited states and the localized defect states. The results of this work demonstrate the ability to control carrier polarization in nonmagnetic metal oxide nanocrystals using both individual and collective electronic properties and allow for their application as an emerging class of multifunctional materials with strongly interacting degrees of freedom.

Interaction between a plasmon, as a collective property of charge carriers, and electronic or spin states in complex nanostructures has emerged as one of the fascinating topics that intertwines the fields of photonics, optoelectronics, and spintronics. Here, we investigate the magneto-optical properties of plasmonic InN and Cu2–x Se nanocrystals and show that the complete exciton polarization induced by cyclotron motion of free carriers is a universal phenomenon in semiconductor nanocrystals. The selective exciton polarization is governed by the angular momentum transfer from the carriers following cyclotron orbits to the excited electronic band states and can be controlled by carrier type (electrons or holes), mass, and velocity. The results of this work demonstrate the free-carrier-induced control of the states around the Fermi level and the exciton polarization in technologically important III–V nanocrystals, allowing for new ways of tailoring quantum states for spintronic and optoelectronic applications.

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