Spin-dependent tunneling into an empty lateral quantum dot

In a recent experiment [Phys. Rev. B {\bf 78}, 041306(R) (2008)] Amasha {\it et al.} reported a strong spin dependence of the rate for electrons to tunnel into an empty quantum dot in a Zeeman field. Such dependence is intriguing, as one expects tunneling rates to depend on the orbital structure of the wavefunction, over which a Zeeman field has no effect. In search for an explanation, we find two mechanisms leading to a spin-dependent tunneling rate. The first originates from different electronic $g$-factors in the lead and in the dot, and favors the tunneling into the spin ground (excited) state when the $g$-factor magnitude is larger (smaller) in the lead. The second is triggered by spin-orbit interactions via the opening of off-diagonal spin-tunneling channels. It systematically favors the spin excited state. Numerically modeling the experimental setup, we find that in GaAs the spin-orbit interaction is unable to explain the experimental results, as it leads to no more than a $\sim$10\% discrepancy in the spin up vs spin down tunneling rates. We conjecture that the significantly larger discrepancy observed experimentally originates from the enhancement of the $g$-factor in the laterally confined lead. Reference: P. Stano and Ph. Jacquod, Phys. Rev. {\bf B} 82, 125309 (2010)