Quantum Electronic Transport through a Precessing Spin

The conductance through a local nuclear spin precessing in a magnetic field is studied by using the equations-of-motion approach. The characteristics of the conductance is determined by the tunneling matrix and the position of equilibrium chemical potential. We find that the spin-flip coupling between the electrons on the spin site and the leads produces the conductance oscillation. When the spin is precessing in the magnetic field at Larmor frequency (${\omega }_L$), the conductance develops the oscillation with the frequency of both ${\omega }_L$ and $2{\omega }_L$ components, the relative spectrum weight of which can be tuned by the chemical potential and the spin-flip coupling.

Figure 1

Magnetic spin coupled to two leads. In the presence of a magnetic field $\mathbf{B}$, the spin precesses around the field direction.

Figure 2

Conductance versus the chemical potential $\mu$ with various values of the spin-flip coupling ${\Gamma }_s/{\Gamma }_n=0.0$ (red solid line), 0.4 (green dashed line), and 0.8 (blue dotted line). The results shown in panels (a) through (c) correspond to three different local spin orientations in zero magnetic field: $(\theta ,{\phi }_0)=(0,0)$, $(\pi /4,0)$, $(\pi /2,0)$. The spin-conserved coupling, ${\Gamma }_n=0.1$.

Figure 3

Conductance versus the phase $\phi$ accumulated by the precession of the local spin with various values of the spin-flip coupling ${\Gamma }_s/{\Gamma }_n=0.0$ (solid line), 0.4 (dashed line), and 0.8 (dotted line). The results shown in the left panels (a) through (c) correspond to three different values of the chemical potential: $\mu =0$, 0.4, and 0.8. Shown in the right panels are the Fourier spectrum of the conductance for ${\Gamma }_s/{\Gamma }_n=0.4$ with the same chemical potential values in the left panels. Other parameter values: ${\Gamma }_n=0.1$, $\theta =\pi /2$, and ${\phi }_0=0$.