[1Dp01-09] Surface Science(SS1) Physical Property

[1Dp01] Two-dimensional heavy fermion in a monoatomic-layer Kondo
lattice YbCu₂

*Takuto Nakamura^1,2, Hiroki Sugihara², Yitong Chen², Ryu Yukawa³, Yoshiyuki Ohtsubo⁴, Kiyohisa Tanaka⁵, Miho Kitamura⁶, Hiroshi Kumigashira⁷, Shin-ichi Kimura^1,2,5 (1. Graduate School of Frontier Biosciences, Osaka University, 2. Department of Physics, Osaka University, 3. Graduate School of Engineering, Osaka University, 4. National Institutes for Quantum Science and Technology,, 5. Institute for Molecular Science, 6. Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 7. Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University)

Heavy fermion (HF) systems, in which massive effective carriers appear due to the Kondo effect, have fascionated many reserchers. Dimensionality is also an important characteristic of the HF system, especially because it is strongly related to quantum criticality. However, the realization of the perfect two dimensional (2D) HF materials is still a challenging topic. Here, we report the surface electronic structure of the monoatomic layer Kondo lattice YbCu₂ on a Cu(111) surface observed by synchrotron-based angle-resolved photoelectron spectroscopy. The 2D conducting band and the Yb 4f state, located very close to the Fermi level, are observed. These bands are hybridized at low temperature, forming the 2D HF state, with an evaluated coherent temperature of about 30 K. The effective mass of the 2D state is enhanced by a factor of 100 by the developmentof the HF state. Furthermore, clear evidence of the hybridization gap formation in the temperature dependence of the Kondo-resonance peak has been observed below the coherent temperature.