Impact of a circularly polarized cavity photon field on the charge and spin flow through an Aharonov–Casher ring

• Transport of spin–orbit coupled electrons interacting with cavity photons.
• Photonic charge current vortices in finite-width quantum ring connected to leads.
• Circularly polarized photon field increases spin polarization and spin photocurrents.
• Threefold Aharonov–Casher charge current dip for circularly polarized photon field.
• Wide-range Aharonov–Casher phase sensitivity of the persistent charge photocurrent.

We explore the influence of a circularly polarized cavity photon field on the transport properties of a finite-width ring, in which the electrons are subject to spin–orbit and Coulomb interaction. The quantum ring is embedded in an electromagnetic cavity and described by “exact” numerical diagonalization. We study the case that the cavity photon field is circularly polarized and compare it to the linearly polarized case. The quantum device is moreover coupled to external, electrically biased leads. The time propagation in the transient regime is described by a non-Markovian generalized master equation. We find that the spin polarization and the spin photocurrents of the quantum ring are largest for circularly polarized photon field and destructive Aharonov–Casher (AC) phase interference. The charge current suppression dip due to the destructive AC phase becomes threefold under the circularly polarized photon field as the interaction of the electrons׳ angular momentum and spin angular momentum of light causes many-body level splitting leading to three many-body level crossing locations instead of one. The circular charge current inside the ring, which is induced by the circularly polarized photon field, is found to be suppressed in a much wider range around the destructive AC phase than the lead-device-lead charge current. The charge current can be directed through one of the two ring arms with the help of the circularly polarized photon field, but is superimposed by vortices of smaller scale. Unlike the charge photocurrent, the flow direction of the spin photocurrent is found to be independent of the handedness of the circularly polarized photon field.

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