An experimental investigation of bulk electronic structure of high-order approximants and quasicrystal*

Approximants, the crystalline analog of quasicrystals, are assumed to represent the quasicrystal phase in the electronic structure calculations and have been very successful to predict the existence of the pseudogap at the Fermi level of the related quasicrystal which is generally considered to stabilize it via the Hume-Rothery mechanism[1]. However, experimental endeavor to explore the bulk electronic structures of approximants, especially of high-order ones is very limited. In this present work, using hard x-ray photoelectron spectroscopy we have investigated the bulk electronic structures of two high-order quaternary approximants of F-type icosahedral (i)-Al-Pd-TM quasicrystal: Al-Pd-Cr-Fe and Al-Pd-Mo-Fe, having similar electron to atom (e/a) ratio as i-Al-Pd-Mn quasicrystal[2]. Both the approximants show a well-formed pseudogap at the Fermi level. Moreover, the pseudogap turns out to be deeper in the approximants compared to i-Al-Pd-Mn, and this is supported by specific heat data. Modifications in the line shape of Al 2s core-level main peak as well as the plasmon loss peaks provide evidence for enhanced hybridization of Al sp and transition metal d states in the approximants than i-Al-Pd-Mn, which could be one of the possible reasons for their larger pseudogap. The absence of magnetic exchange splitting in the Fe 2p core-level spectra establishes the nonmagnetic nature of the approximants.

 1. J. Hafner et al., Phys. Rev. Lett. 68, 2321 (1992) 2. Krajci et al., Phys. Rev. B. 51, 24 (1995) 3. S. Sarkar et al., Phys. Rev. Res. 3, 013151 (2021)