Origin of Quantum Criticality in Yb-Al-Au Approximant Crystal and Quasicrystal

Abstract

To get insight into the mechanism of emergence of unconventional quantum criticality observed in quasicrystal Yb${}_{15}$Al${}_{34}$Au${}_{51}$, the approximant crystal Yb${}_{14}$Al${}_{35}$Au${}_{51}$ is analyzed theoretically. By constructing a minimal model for the approximant crystal, the heavy quasiparticle band is shown to emerge near the Fermi level because of strong correlation of 4f electrons at Yb. We find that charge-transfer mode between 4f electron at Yb on the 3rd shell and 3p electron at Al on the 4th shell in Tsai-type cluster is considerably enhanced with almost flat momentum dependence. The mode-coupling theory shows that magnetic as well as valence susceptibility exhibits $\chi \sim T^{-0.5}$ for zero-field limit and is expressed as a single scaling function of the ratio of temperature to magnetic field $T/B$ over four decades even in the approximant crystal when some condition is satisfied by varying parameters, e.g., by applying pressure. The key origin is clarified to be due to the strong locality of the critical Yb-valence fluctuation and small Brillouin zone reflecting the large unit cell, giving rise to the extremely-small characteristic energy scale. This also gives a natural explanation for the quantum criticality in the quasicrystal corresponding to the infinite limit of the unit-cell size.

5 pages, 4 figures

References in corpus (5)

• Quantum critical state in a magnetic quasicrystal
• Quantum Valence Criticality as Origin of Unconventional Critical Phenomena
• New Universality Class of Quantum Criticality in Ce- and Yb-based Heavy Fermions
• T/B Scaling in beta-YbAlB4
• Wide Quantum Critical Region of Valence Fluctuations: Origin of Robust Quantum Criticality in Quasicrystal Yb15Al34Au51 under Pressure

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• Theory for Non-Fermi Liquid Temperature Dependence in Resistivity of Ce_xLa_{1-x} Cu_{5.62} Au_{0.38} (x=0.02-0.10) on the Local Quantum Valence Criticality of Ce Impurities
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