Effects of Crystalline Electronic Field and Onsite Interorbital Interaction in Yb-based Quasicrystal and Approximant Crystal

TL;DR

This paper investigates the electronic properties and quantum critical phenomena in Yb-based quasicrystals and approximant crystals, emphasizing the role of crystalline electric fields and onsite interorbital interactions in explaining valence fluctuations.

Contribution

It introduces a minimal model incorporating uneven CEF levels and onsite Coulomb interactions, explaining the quantum criticality observed in Yb quasicrystals and approximants.

Findings

Lattice constant dependence of Yb valence matches experimental data.

Yb quasicrystal is at the quantum critical point of valence transition.

Uneven CEF levels influence electronic state behavior.

Abstract

To get an insight into a new type of quantum critical phenomena recently discovered in the quasicrystal Yb$_{15}$Al$_{34}$Au$_{51}$ and approximant crystal (AC) Yb$_{14}$Al$_{35}$Au$_{51}$ under pressure, we discuss the property of the crystalline electronic field (CEF) at Yb in the AC and show that uneven CEF levels at each Yb site can appear because of the Al/Au mixed sites. Then we construct the minimal model for the electronic state on the AC by introducing the onsite Coulomb repulsion between the 4f and 5d orbitals at Yb. Numerical calculation for the ground state shows that the lattice constant dependence of the Yb valence well explains the recent measurement done by systematic substitution of elements of Al and Au in the quasicrystal and AC, where the quasicrystal Yb$_{15}$Al$_{34}$Au$_{51}$ is just located at the point from where the Yb-valence starts to change drastically. Our calculation convincingly demonstrates that this is indeed the evidence that this material is just located at the quantum critical point of the Yb-valence transition.