Electronic states in 1/1 Cd6Yb and 1/1 Cd6Ca: Relativistic, correlation, and structural effects

TL;DR

This study investigates the electronic structure of 1/1 Cd6Yb and Cd6Ca approximants to quasicrystals, emphasizing the importance of relativistic spin-orbit coupling and electronic correlations for accurate modeling and matching experimental photo-emission spectra.

Contribution

It demonstrates that including relativistic spin-orbit interaction and Hubbard U correlations is essential for accurately describing the electronic states in these approximants.

Findings

Spin-orbit interaction causes splitting of Cd-4d and Yb-4f peaks.

Including Hubbard U reproduces experimental peak positions.

Relativistic and correlation effects are crucial for matching photo-emission spectra.

Abstract

The electronic structure of the rational approximants 1/1 Cd6Yb and 1/1 Cd6Ca to the stable icosahedral CdYb and CdCa quasicrystals is studied by the full-potential linear augmented plane wave method. A comparison is made between several structural models. We show that the (relativistic) spin-orbit (SO) interaction and electronic correlations that are not described by the usual local density approximation, are essential for an accurate description of the electronic structure. In particular, we show that the SO interaction is responsible for a splitting of the Cd-4d and Yb-4f peaks, and that the experimental peak positions can be reproduced by including a Hubbard U term in the Hamiltonian [U(Cd) = 5.6 eV, U(Yb) = 3.1 eV]. Our results show very good agreement with a photo-emission (PE) spectrum of 1/1 Cd6Yb [R. Tamura, Y. Murao, S. Takeuchi, T. Kiss, T. Yokoya, and S. Shin, Phys. Rev. B 65, 224207 (2002)] and a 350 eV PE spectrum of 1/1 Cd6Ca, which we present in this paper. Without the relativistic and correlation effects even a qualitative agreement with the PE spectra cannot be achieved.