Concomitant singularities of Yb-valence and magnetism at a critical lattice parameter of icosahedral quasicrystals and approximants

Keiichiro Imura,Yoshiya Yamamoto,Nozomu Hiraoka,Shinnosuke Hirokawa,Hitoshi Yamaoka,Jun’Ichiro Mizuki,Takuma Kawai,Keisuke Namba,Kazushi Sakamoto,Shinjirou Yokota,Hirofumi Ishii,Noriaki K Sato,Kazuhiko Deguchi,Tsutomu Ishimasa

doi:10.1038/s41598-020-74124-7

Abstract

Non-Fermi-liquid (NFL), a significant deviation from Fermi-liquid theory, usually emerges near an order-disorder phase transition at absolute zero. Recently, a diverging susceptibility toward zero temperature was observed in a quasicrystal (QC). Since an electronic long-range ordering is normally absent in QCs, this anomalous behaviour should be a new type of NFL. Here we study high-resolution partial-fluorescence-yield x-ray absorption spectroscopy on Yb-based intermediate-valence icosahedral QCs and cubic approximant crystals (ACs), some of which are new materials, to unveil the mechanism of the NFL. We find that for both forms of QCs and ACs, there is a critical lattice parameter where Yb-valence and magnetism concomitantly exhibit singularities, suggesting a critical-valence-fluctuation-induced NFL. The present result provides an intriguing structure–property relationship of matter; size of a Tsai-type cluster (that is a common local structure to both forms) tunes the NFL whereas translational symmetry (that is present in ACs but absent in QCs) determines the nature of the NFL against the external/chemical pressure.

Highlights

Non-Fermi-liquid (NFL), a significant deviation from Fermi-liquid theory, usually emerges near an order-disorder phase transition at absolute zero
Powder x-ray diffraction (XRD) measurements, which were conducted at room temperature, showed that samples prepared here have the same pattern as the Tsai-type cluster based Au–Al–Yb QC/approximant crystals (ACs) and (Au/Cu)–Al–Yb Q C15,26
This result leads us to suggest that the Yb mean-valence anomaly at a6D/a6cD = 1 ( a3D/a3cD = 1 ) is due to the local structure such as the cluster size, rather than the difference in the global structural property between the QCs and the ACs

Summary

Introduction

Non-Fermi-liquid (NFL), a significant deviation from Fermi-liquid theory, usually emerges near an order-disorder phase transition at absolute zero. Since an electronic long-range ordering is normally absent in QCs, this anomalous behaviour should be a new type of NFL. In the vicinity of a quantum critical point (QCP), for example, a magnetic QCP where a Néel temperature continuously vanishes to zero, such a FL feature is modified by order-parameter fluctuations coupled with low-energy electronhole excitations around the Fermi level, into another form of C/T ∝ −T1/2 and χ ∝ −T1/4 in the case of a threedimensional (3D) c ase[1]. QCs are metallic alloys that possess long-range quasiperiodic structure with specific diffraction symmetry such as five- or tenfold rotational symmetry that is incompatible with translational symmetry and forbidden to periodic crystals[12,13]. Yb atoms are located on the vertices of the icosahedron, and the edge length connecting Yb atoms is approximately 0.55 nm (Ref.[6]) These clusters are aligned over long distances as evidenced by the sharp diffraction spots as mentioned above. Quasiperiodic structures can be produced by projecting 6D hypercubic lattices onto 3D space[16,17], meaning that QCs are characterised by 6D lattice parameter a6D

Objectives

Methods

Results

Conclusion