Evolution of Kondo Resonance from a Single Impurity Molecule to the Two-Dimensional Lattice

The successive spectral evolution of the Kondo resonance state was investigated from a single iron(II) phthalocyanine molecule to the two-dimensional lattice on Au(111) by interrogating the individual molecules with a scanning tunneling microscope. A sharp Kondo peak appears in the single-impurity regime, which broadens and splits as the lattice builds up. The origin of spectral evolution together with the electronic ground state of the lattice are discussed based on the competition of the Kondo effect and Rudermann-Kittel-Kasuya-Yosida coupling between the molecular spins.

Figure 1

(a) STM topographic image of FePc ($I_t=100\mathrm{pA}$, $V_s=-0.1\mathrm{V}$, $20\mathrm{nm}\times 20\mathrm{nm}$). The dots show the substrate lattice. (b) A series of STS spectra of FePc taken at 0.4–6.0 K by keeping the STM tip over the Fe atom with $V_{\mathrm{rms}}=200\mu \mathrm{V}$ (312.6 Hz) added to $V_s$. The red lines show the calculated Fano line shape.

Figure 2

(a) STM topographic image in the submonolayer regime taken at 0.4 K ($I_t=100\mathrm{pA}$, $V_s=-100\mathrm{mV}$, $20\mathrm{nm}\times 20\mathrm{nm}$). (b) The $N_{\mathrm{nn}}$ dependence of STS spectra of FePc taken at 0.4 K in the cluster shown by the square in (a). (c) STM topographic image in the submonolayer regime taken at 0.4 K ($I_t=80\mathrm{pA}$, $V_s=-100\mathrm{mV}$, $15\mathrm{nm}\times 15\mathrm{nm}$). (d) STS spectra of individual FePc marked by squares, triangles and circles in (c). The molecules specified by the same marker exhibit basically the same spectrum. The STS spectra in (b) and (d) were measured by keeping the tip over the Fe atom with $V_{\mathrm{rms}}=200\mu \mathrm{V}$ (312.6 Hz) added to $V_s$.

Figure 3

(a) STM topographic image of FePc superlattice taken at 0.4 K ($I_t=40\mathrm{pA}$, $V_s=-100\mathrm{mV}$, $10\mathrm{nm}\times 10\mathrm{nm}$). The dark region in the center is a vacancy. (b) A series of STS spectra taken at 0.4 K by keeping the tip over the positions marked by (i)–(x) in (a). (c) Temperature dependence of STS spectra taken at 0.4–9.6 K by keeping the tip over the Fe atom of FePc inside the superlattice ($V_{\mathrm{rms}}=200\mu \mathrm{V}$ and 312.6 Hz).

Figure 4

(a) The spatial distribution of $dI/dV$ intensity at $V_s=-1.5\mathrm{mV}$ ($10\mathrm{nm}\times 10\mathrm{nm}$). The darker holes correspond to the brighter spots (Fe atoms) in (b) STM topographic image taken simultaneously.