Systematic investigation of physical properties of YbB_6±x using the combinatorial approach

Rare-earth boride systems have gained tremendous interest for exploring exotic and novel physical phenomena such as mixed valence states, heavy fermion, strong correlation and superconductivity. Since samarium hexaboride (SmB₆) has turned out to be a topological insulator, ytterbium boride (YbB_x) systems have been intensively studied as another possible topological insulator. However, the existence of the topologically protected surface states of YbB₆ is yet to be confirmed, and the origin of the quantum oscillations in Kondo insulator YbB₁₂ remains unresolved. We are systematically investigating the physical properties of YbB_6±x depending on stoichiometry using the thin-film combinatorial approach. The composition spread YbB_6±x thin films were fabricated by the co-sputtering of YbB₆ and B targets. The composition mapping of the spread films is performed using wavelength dispersive X-ray spectroscopy (WDS), and synchrotron x-ray diffraction measurements are employed for structural mapping analysis. We will discuss the electrical behavior of YbB_6±x with the change in the valence state of Yb ion depending on the stoichiometry.