X-ray atomic orbital analysis of 4f and 5d electron configuration of SmB_6 at 100, 165, 230 and 298 K

摘要

Accurate electron-density measurement of SmB6 at 100, 165, 230 and 298 K, and X-ray atomic orbital (XAO) analysis were carried out. The 4f-electron density around Sm and 5d electron density at ～1 ? from Sm were analysed by XAO analysis. The 5d electron density is due to the electrons of the 5d J = 5/28 orbitals which stem from the e g orbitals in the strong field approximation. The change in electron populations of the 5d 5/28 orbitals with temperature is similar to that of the resistivity. Since the conduction band consists of 5d 5/28 and B-2p orbitals according to band theory, this indicates that the larger populations of the 5d 5/28 orbitals correspond to the larger number of localized electrons and are correlated to the resistivity of SmB6. The occupation of the bulky 5d 5/28 orbitals may be the reason for the elongation of the lattice parameter below 150 K. The 4f 7/26 orbitals are obviously occupied except at 100 K, which seems to be caused by the energy gap between 4f 5/2 and 4f 7/2 states, which begins to exist between 100 and 150 K, and may represent one of the properties of a Kondo insulator.