Hard x-ray photoemission study of Yb_1−xZr_xB₁₂: the effects of electron doping on the Kondo insulator YbB₁₂

Abstract

We have carried out hard x-ray photoemission spectroscopy (HAXPES) of Yb Zr B ([Formula: see text]) to study the effects of electron doping on the Kondo insulator YbB. The Yb valences of Yb Zr B at 300 K estimated from the Yb 3d HAXPES spectra decreased after substituting Yb with Zr from 2.93 for YbB to 2.83 for YbZrB. A temperature dependent valence decrease was found upon cooling for all doping concentrations. We found peak shifts of the B 1s and Zr 3d, and Yb 4f spectra toward the deeper binding-energy with increasing Zr concentration, which indicates a shift of the Fermi level to the higher energy and that of the Yb 4f hole level close to the Fermi level, respectively, due to electron doping. These results qualitatively show the enhanced hybridization between the Yb 4f and conduction-band states with Zr substitution, consistent with magnetic susceptibility measurements.

Electronic structure of YbFe$_4$Al$_8$ antiferromagnet: A combined X-ray photoelectron spectroscopy and first-principles study

“…It is not uncommon to put the same material into both categories based on similar experimental results, where a well-known example is YbAl 3 [12][13][14]. A valence band, similar to the one observed for YbFe 4 Al 8 [15], consisting of contributions from Yb 2+ and Yb 3+ has been seen previously for both materials classified as valence fluctuating, such as YbCu 2 Si 2 [16], YbAl 2 [17,18], YbB 12 [19], Yb 2 Pt 6 Ga 15 and Yb 2 Pt 6 Al 15 [20], as well as for materials of intermediate valence, such as YbFe 4 Sb 12 [21], YbInCu 4 [22], YbNi 0.8 Al 4.2 [23], YbRh 2 Si 2 [11], Yb 4 Ga 24 Pt 9 [24], and Yb 2 Si 2 Al [10]. Since our experimental analysis is based solely on XPS measurements, we cannot unambiguously resolve the membership of the compound under consideration, YbFe 4 Al 8 , in the class of fluctuating or intermediate valence materials.…”

Fine details of crystal structure and atomic vibrations in YbB12with a metal–insulator transition

“…Most rare-earth dodecaborides with incompletely occupied 4f shells are highly conductive metals with antiferromagnetic ground state at low temperatures. The only exception is YbB 12 , which is known as a Kondo insulator (Aeppli & Fisk, 1992), where Yb takes an intermediate valence 2.92-2.95 (Iga et al, 1998;Yamaguchi et al, 2009;Hagiwara et al, 2017;Rousuli et al, 2017). At room temperature, it is a metal with spin fluctuations on ytterbium ions.…”

“…There are several models proposed to explain the non-magnetic insulating nature of YbB 12 at low temperatures. One of them is based on the coherent band picture where the energy gap is formed due to strong d-f hybridization (Grewe & Steglich, 1991;Saso & Harima, 2003). The inversion between 4f and 5d states that accompanies this process is considered as an essential characteristic of a topological Kondo insulator (Lu et al, 2013;Weng et al, 2014;Hagiwara et al, 2016).…”