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The physical mechanism driving the $\gamma$-$\alpha$ phase transition offace-centre-cubic (fcc) cerium (Ce) remains controversial until now. In thiswork, high quality single crystalline fcc-Ce thin films were grown onGraphene/6$H$-SiC(0001) substrate, and explored by XRD and ARPES measurement.XRD spectra showed a clear $\gamma$-$\alpha$ phase transition at$T_{\gamma-\alpha}\approx$ 50 K, which is retarded by strain effect fromsubstrate comparing with $T_{\gamma-\alpha}$ (about 140 K) of the bulk Cemetal. However, APRES spectra did not show any signature of $\alpha$-phaseemerging in the surface-layer from 300 K to 17 K, which implied that$\alpha$-phase might form at the bulk-layer of our Ce thin films. Besides, anevident Kondo dip near Fermi energy was observed in the APRES spectrum at 80 K,indicting the formation of Kondo singlet states in $\gamma$-Ce. Furthermore,the DFT+DMFT calculations were performed to simulate the electronic structuresand the theoretical spectral functions agreed well with the experimental ARPESspectra. In $\gamma$-Ce, the behavior of the self-energy's imaginary part atlow frequency not only confirmed that the Kondo singlet states emerged at$T_{\rm KS} \geq 80$ K, but also implied that they became coherent states at alower characteristic temperature ($T_{\rm coh}\sim 40$ K) due to the indirectRKKY interaction among $f$-$f$ electrons. Besides, $T_{\rm coh}$ from thetheoretical simulation was close to $T_{\gamma-\alpha}$ from the XRD spectra.These issues suggested that the Kondo scenario might play an important role inthe $\gamma$-$\alpha$ phase transition of cerium thin films.

Kondo scenario of the {\gamma}-{\alpha} phase transition in single crystalline Cerium thin films