Electronic state of an organic molecular magnet: Soft x-ray spectroscopy study of $\alpha$-TDAE-C${}_{60}$ single crystal

Soft x-ray photoelectron spectroscopy was performed for $\alpha$-TDAE-C${}_{60}$ single crystal. A C $1s$ spectrum with a shakeup satellite of TDAE-C${}_{60}$ is very similar to that of C${}_{60}$ when we shift the energy, indicating a charge transfer to the C${}_{60}$ site. A comparison of a N $1s$ spectrum with theoretical calculations indicates that TDAE mainly consists of the TDAE${}^{+}$ state. The valence-band spectrum near the Fermi edge also suggests a charge transfer from the TDAE to the C${}_{60}$ cage. Based on these results we propose a modified model for the charge transfer: the charge states of C${{}_{60}}^{-}$ and TDAE${}^{+}$, and the dimer formation along the $c$ axis between the TDAE${}^{+}$ states.

Figure 1

N $1s$ photoelectron spectra at $h\nu =797$ eV for fractured (solid line) and nonfractured (dotted line) crystals. The data for the crushed powder sample by Hino et al. is also shown for comparison (Ref. 21).

Figure 2

(a) C $1s$ photoelectron spectra. (b) Enlargement of the shakeup satellite part. Note that the spectrum of the C${}_{60}$ film is shifted by 0.4 eV.

Figure 3

(a) Valence spectra of a TDAE-C${}_{60}$ crystal. (b) Enlargement of the spectra around the Fermi edge. The open circles are experimental data. The solid line for the present data corresponds to five-point smoothed curve. The dashed line corresponds to the mean value of the background above the Fermi edge.

Figure 4

Models of the charge transfer. (a) Mixing of configurations of a weakly doped system (Ref. 26). (b) Our proposed model. TDAE${}^{+}$ ions are weakly bonded, forming a dimer.