Room Temperature Electrical Detection of Spin Coherence in ${\mathrm{C}}_{60}$

An experimental demonstration of electrical detection of coherent spin motion of weakly coupled, localized electron spins in thin fullerene ${\mathrm{C}}_{60}$ films at room temperature is presented. Pulsed electrically detected magnetic resonance experiments on vertical photocurrents through $\mathrm{Al}/{\mathrm{C}}_{60}/\mathrm{ZnO}$ samples showed that an electron spin Rabi oscillation is reflected by transient current changes. The nature of possible microscopic mechanisms responsible for this spin to charge conversion as well as its implications for the readout of endohedral fullerene ($\mathrm{N}@{\mathrm{C}}_{60}$) spin qubits are discussed.

Figure 1

Transient current $\Delta I$ of a $\mathrm{N}@{\mathrm{C}}_{60}$ film illuminated with a halogen lamp ($\approx 10\mathrm{mW}/{\mathrm{cm}}^2$, $I_0=10\mu \mathrm{A}$) after 320 ns long microwave pulses ($B_1\approx 63\mu \mathrm{T}$). Time traces (a) were recorded at different magnetic fields $B_0$ to afford the 2D data set (b). 1D cuts along the field dimension (c) reveal the spectral behavior. (d) Displays a global fit of the data in (b) together with an indication where the cuts (a),(c) were taken; in these, the data are represented by markers, whereas the global fit is drawn as lines.

Figure 2

(a) Oscillatory part of the observable $Q$ as a function of microwave pulse length at different pulse amplitudes $B_1$ for a ${\mathrm{C}}_{60}$ film illuminated with an argon ion laser ($<100\mathrm{mW}/{\mathrm{cm}}^2$, $I_0=50\mu \mathrm{A}$). The lines are fits using the theoretical curve $T(\alpha =\kappa \gamma B_1\tau )$ given in Eq. (3). (b) Fast Fourier transforms of the data in (a) and Lorentzian fits. (c) Rabi frequencies $f_R$ (open symbols) and resonance widths $\Delta f_R$ (solid symbols) extracted from the fits in (b). The full line in (c) is $f_R=\gamma B_1/2\pi$, the expected behavior of a spin $S=\frac{1}{2}$. The dotted line is the prediction of the linewidth as a function of $B_1$ based on the assumption of a $\approx 15\%$ field inhomogeneity.

Figure 3

(a) Schematic illustration of an electrical readout of a $\mathrm{N}@{\mathrm{C}}_{60}$ endohedral fullerene spin. The localized spin involved in spin-dependent transitions, marked by a surrounding sphere, is dipolarly coupled to the adjacent $\mathrm{N}@{\mathrm{C}}_{60}$ spin. (b) The expected spectrum for 52 MHz strong coupling of the $S=\frac{3}{2}$ $\mathrm{N}@{\mathrm{C}}_{60}$ spin to an $S=\frac{1}{2}$ state in ${\mathrm{C}}_{60}$.