Single-Electron Transport in Electrically Tunable Nanomagnets

We study a single-electron transistor (SET) based upon a II–VI semiconductor quantum dot doped with a single-Mn ion. We present evidence that this system behaves like a quantum nanomagnet whose total spin and magnetic anisotropy depend dramatically both on the number of carriers and their orbital nature. Thereby, the magnetic properties of the nanomagnet can be controlled electrically. Conversely, the electrical properties of this SET depend on the quantum state of the Mn spin, giving rise to spin-dependent charging energies and hysteresis in the Coulomb blockade oscillations of the linear conductance.

Figure 1

Low-energy spectra of ${\mathcal{H}}_{\mathrm{QD}}$ for dot A (circles) with $\mathcal{Q}=-1$ (a), $Q=+1$ (b), and $Q=+3$ (c). Notice the different vertical scale in (a) and (b) In panel (b) we also show the spectrum of QD B with $Q=+1$ (squares). The Kohn-Luttinger parameter for CdTe are ${\gamma }_1=4.14$, ${\gamma }_2=1.09$, and ${\gamma }_3=1.62$ and the spin orbit interaction is $\Delta =950\mathrm{meV}$. We take $J_e=-15\mathrm{eV}{\AA }^3$ and $J_h=60\mathrm{eV}{\AA }^3$.

Figure 2

$G_0(V_G)$ (upper panels), charge (middle panels), and diagonal terms of the $\rho$ (lower panels) for QD A as a function of $V_G$ around the $Q=-1\leftrightarrow 0$ transition (left) and $Q=0\leftrightarrow +1$ (right). Lower panels: solid (dashed) lines correspond to $\mathcal{Q}=0$ ($|\mathcal{Q}|=1$) states. Results obtained with ${\Gamma }_L={\Gamma }_R=0.01\mathrm{meV}$ and $k_{B}T=0.05\mathrm{meV}$.

Figure 3

Current and differential conductance as a function of bias for QD A (a),(b),(c) at various charge states and QD B (d) (see text).