Two-dimensional heavy fermion in a monoatomic-layer Kondo lattice YbCu${}_2$

Abstract

The Kondo effect between localized $f$-electrons and conductive carriers leads to exotic physical phenomena. Among them, heavy-fermion (HF) systems, in which massive effective carriers appear due to the Kondo effect, have fascinated many researchers. Dimensionality is also an important characteristic of the HF system, especially because it is strongly related to quantum criticality [S. Sachdev, Science 288, 475 (2000)]. However, perfect two-dimensional (2D) HF materials have not been reported yet. Here, we report the surface electronic structure of the monoatomic-layer Kondo lattice YbCu${}_2$ on a Cu(111) surface observed by synchrotron-based angle-resolved photoelectron spectroscopy. The 2D conducting band and the Yb 4$f$ 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 development of 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. Our study provides a new candidate as an ideal 2D HF material for understanding the Kondo effect at low dimensions.

24 pages, 10 figures

References in corpus (8)

• Gate-tunable heavy fermions in a moiré Kondo lattice
• Pressure-Induced Valence Crossover and Novel Metamagnetic Behavior near the Antiferromagnetic Quantum Phase Transition of YbNi${}_3$Ga${}_9$
• Field induced density wave in the heavy fermion compound CeRhIn5
• Quantum-well states at the surface of the heavy-fermion superconductor URu${}_2$Si${}_2$
• Kondo hybridization and quantum criticality in $\beta$-YbAlB${}_4$ by laser-ARPES
• Valence state determines the band magnetocrystalline anisotropy in 2D rare-earth/noble-metal compounds
• Tunable Kondo resonance at a pristine two-dimensional Dirac semimetal on a Kondo insulator
• Atomic and mesoscopic structure of Dy-based surface alloys on noble metals

Cited by in corpus (1)

• Dimensionality tuning of heavy-fermion states in ultrathin CeSi2 films