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Séminaire MCBT

Mardi 8 janvier à 11h00
Salle Louis Weil, E424

Orateur : Kazuhiko DEGUCHI (Nagoya University)
"Quantum Critical Phenomenon in a Magnetic Au-Al-Yb Quasicrystal"

Quasicrystals are metallic alloys that possess long-range, aperiodic structures with diffraction symmetries forbidden to conventional crystals. Since the discovery of quasicrystals by Schechtman et al. at 1984 (ref. 1), there has been considerable progress in resolving their geometric structure. For example, it is well known that the golden ratio of mathematics and art occurs over and over again in their crystal structure. Due to this quasi-periodicity, an unusual electronic state that is neither extended nor localized is expected ; neither they are extended as in periodic crystals nor localized as in amorphous materials. However, such an unusual state has not yet been observed. The quasicrystal that we study here is a gold-aluminum-ytterbium alloy described as Au51Al34Yb15 [2]. In the present study, we report the first observation of quantum (T = 0) critical phenomena of the Au-Al-Yb quasicrystal −the magnetic susceptibility and the electronic specific heat coefficient arising from strongly correlated 4f electrons of the Yb atoms diverge as T → 0. Furthermore, we observe that this quantum critical phenomenon is robust against hydrostatic pressure. By contrast, there is no such divergence in a crystalline approximant Au51Al35Yb14, a phase whose composition is close to that of the quasicrystal and whose unit cell has atomic decorations (i.e., icosahedral clusters of atoms) that look like the quasicrystal. We propose a peculiar quantum critical behaviour of the Au-Al-Yb quasicrystal to reflect this unusual state expected for quasicrystals. It becomes apparent in the present system because of strong correlations induced by the 4f electrons of Yb. These results clearly indicate that the quantum criticality is associated with the unique electronic state of quasicrystal, i.e., a spatially confined critical state [3]. Finally we discuss the possibility that there is a general law underlying the conventional crystals and the quasicrystals.

[1] D. Shechtman et al., Phys. Rev. Lett. 53, 1951 (1984).
[2] T. Ishimasa et al., Phil. Mag. 91, 4218 (2011).
[3] K. Deguchi et al., Nature Materials 11, 1013 (2012).

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