DFT computations

The DFT calculations for YbCl₃ monolayer were carried out to elucidate the electronic structure and make a comparison with experimental dI/dV spectra, using the full-potential augmented plane wave plus local orbital code (Wien2k)⁴². According to the experimentally resolved lattice constant of 6.65 ± 0.1 Å, we adopted the YbCl₃ lattice parameters of a = b = 6.65 Å for computation and optimized the atomic positions. The plane wave cutoff energy of 14 Ry was set for the interstitial wave functions, and 11*11*1 k-mesh was used for integration over the Brillouin zone. The muffin-tin sphere radii were chosen to be 2.5 and 2.0 Bohr for Yb and Cl atoms, respectively. We performed LSDA + U + SOC calculations with the typical values Hubbard U = 8.5 eV and Hund exchange J_H = 1.0 eV for Yb 4 f electrons⁴³, and the spin–orbit–coupling (SOC) effect was included by the second-variational method with scalar relativistic wave functions.