Spin Current from Quantum Dots Embedded in a Microcavity

Spin Current from Quantum Dots Embedded in a Microcavity

Chris P. Search
Department of Physics and Engineering Physics,
Stevens Institute of Technology, Hoboken, NJ 07030

Experiments on self-assembled quantum dots have recently resulted in electrical control of the charge state of dots embedded in microcavities as well as studies of the conductance and shot noise through these structures. At the same time, a number of experiments have shown strong coupling to a single optical microcavity mode. This work has motivated us to study theoretically how electrical transport through a quantum dot would be effected by coupling to a cavity mode. We have developed a model for quantum dots coupled to doped leads at zero bias with one of the Zeeman states lying below the Fermi level of the leads and the other above. Raman transitions involving a pump laser and a quantized cavity mode induce spin flips inside the dot that result in a pure spin current flowing from the dot. We have studied the characteristics of the spin current generated by this quantum dot spin battery for the case where (i) a spin flip is associated with emission of a photon into the cavity mode and absorption from the pump (ii) the spin flip is caused by absorption of a photon from the cavity and emission into the pump. In the former case, we calculate the spin current and the photon current associated with the photons leaking out of the cavity as well as the associated shot noise. We find that in our system, the spin current can be significantly larger than for the case of spin flips induced by classical driving fields. The frequency dependent current shot noise show dips and peaks that are a result of the discrete nature of photons. In the latter case, we find that the cavity mode and the spin current exhibit bistability as a function of the laser amplitude, which is driving the cavity mode.